Tribikram Kundu

Interests

Research

Dr. Kundu has made significant and original contributions in both basic and applied research in structural health monitoring (SHM) and nondestructive testing techniques (NDT) for material characterization by ultrasonic and electromagnetic waves. His research interests include acoustic microscopy, elastic wave propagation in multilayered solids, fracture mechanics, computational mechanics, and numerical modeling. Application areas of his research findings can be in aerospace materials, civil and structural materials, geomaterials, electronic as well as biological materials. His research on biological material characterization has also received international acclaim. He has won the Humboldt research prize (also known as the Senior Scientist Award) from Germany for his research on biological cell characterization. He has developed a new mesh-free semi-analytical/numerical technique called distributed point source method (DPSM) in collaboration with his French colleagues. This technique has been found to be superior to the finite element method (FEM) for solving many ultrasonic, electrostatic and electro-magnetic problems. He has co-authored the first book on DPSM.Dr. Kundu has collaborated with European scientists on theoretical and experimental research on engineering and biological materials. Most of his European collaborations have been funded by foreign funding agencies in Germany (Alexander von Humboldt Foundation), Belgium (NATO, North Atlantic Treaty Organization), France (French Ministry of Education), Denmark (Aarhus University Medical School), Spain, Poland, Sweden, Switzerland, Japan, South Korea, India and China. Among domestic sources, the National Science Foundation and the Air Force Office of Scientific Research have provided the lion share of his research funding. Besides Humboldt Research Prize he has won the NDE Life Time Achievement Award from SPIE and Research Award for Sustained Excellence from ASNT for his research contributions.

Teaching

Professor Kundu has taught a variety of courses on mechanics and numerical methods. These include undergraduate courses on Statics, Dynamics, Strength of Material, Numerical Analysis with MATLAB, Structural Analysis, and Finite Element Method. At the graduate level he has taught courses on Continuum Mechanics, Elasticity, Plasticity, Advanced Finite Element Analysis, Fracture Mechanics and Elastic Wave Propagation in Solids. He has developed the last three graduate courses at the University of Arizona and thoroughly revised the first three. He has authored a textbook on fracture mechanics that also includes elasticity theory in its first chapter, co-authored a textbook on Introductory Finite Element Method and edited a book on Ultrasonic Nondestructive Evaluation that can be used as a textbook for a graduate level course on elastic waves. He has supervised 22 MS students (2 jointly), 34 PhD students (9 jointly and 3 in Foreign Institutes), and 7 post-doctoral research scholars. He is currently supervising 2 MS and 4 PhD (1 jointly) students. In 1999 his MS student (Y.C. Jung) received the best MS thesis award at the University of Arizona. Only one MS thesis was selected for this award in 1999 among all fields of science, engineering and humanities. In three consecutive years 2000, 2001 and 2002 his PhD student C. M. Dao received the Bill Gates Millennium scholarship and was selected for the Outstanding Graduate Student of the CEEM (Civil Engineering & Engineering Mechanics) Department in 2007. His PhD students Samik Das and Ehsan Kabiri Rahani also received the Outstanding Graduate Student of the CEEM Department award in 2008 and 2011, respectively. In 2009 he received the outstanding faculty award for his teaching, selected by the undergraduate students of the CEEM department. In the year 2000 Dr. Kundu received a Letter of Commendation from the Graduate College of the University of Arizona for his contributions in graduate teaching, research and mentoring activities. In May 2002 he received a special recognition as the Outstanding Honors Faculty, awarded by the University of Arizona and the Honors College for his ‘outstanding and dedicated service in guiding undergraduate students of the Honors College’. His former graduate students are now faculty members in USA (University of South Carolina, California State University at Northridge, North Carolina State University and State University of New York at Buffalo), and abroad - South Korea, India, Brazil, Qatar and Turkey.

Courses

Scholarly Contributions

Books

• Kundu, T. (2019). Mechanics of Elastic Waves and Ultrasonic Nondestructive Evaluation. CRC Press, Taylor and Francis Group.
  More info

  Mechanics of Elastic Waves and Ultrasonic Nondestructive Evaluation by T. Kundu, Pub. CRC Press, Taylor and Francis Group, ISBN: 9781138035942, 2019
• Kundu, T. (2019). Nonlinear Ultrasonic and Vibro-Acoustical Techniques for Nondestructive Evaluation. Switzerland: Springer Nature.
  More info

  Nonlinear Ultrasonic and Vibro-Acoustical Techniques for Nondestructive Evaluation, Ed. T. Kundu, Pub. Springer Nature, Switzerland, 2019, ISBN 978-3-319-94476-0, https://www.springer.com/us/book/9783319944746
• Kundu, T. (2018). Health Monitoring of Structural and Biological Systems XII. SPIE.
  More info

  This book is the proceedings of a conference (containing all papers presented at the SPIE conference on structural health monitoring) that was chaired by me
• Kundu, T. (2017). Health Monitoring of Structural and Biological Systems 2017.
  More info

  This book is the complete proceedings - or collection of all papers presented at the SPIE Structural Health monitoring conference that I chaired
• Kundu, T. (2016). Health Monitoring of Structural and Biological Systems 2016.
  More info

  This is a complete conference proceedings containing all papers presented at the SPIE's structural health monitoring conference that was chaired by me
• Darvennes, C., & Kundu, T. (2001). Proceedings of the 7th ASME NDE Topical Conference: Presented at the 7th ASME NDE Topical Conference, San Antonio, Texas, April 23-25, 2001. American Society of Mechanical Engineers.
• Qu, J., & Kundu, T. (2000). Nondestructive evaluation and characterization of engineering materials for reliability and durability predictions: presented at the 2000 ASME International Mechanical Engineering Congress and Exposition, November 5-10, 2000, Orlando, Florida. Amer Society of Mechanical.

Chapters

• Glisic, B., & Kundu, T. (2022). Sensing solutions for assessing and monitoring pipeline systems. In Sensor technologies for civil infrastructures(pp 255--297). Woodhead Publishing.
• Romanel, C., & Kundu, T. (2021). A hybrid method for dynamic soil-structure interaction. In Applications of Computational Mechanics in Geotechnical Engineering(pp 439--452). Routledge.
• Eiras, J. N., Kundu, T., Popovics, J. S., & Pay'a, J. (2019). Cement-Based Material Characterization Using Nonlinear Single-Impact Resonant Acoustic Spectroscopy (NSIRAS). In Nonlinear Ultrasonic and Vibro-Acoustical Techniques for Nondestructive Evaluation(pp 487--508). Springer, Cham.
• Kundu, T., Eiras, J. N., Li, W., Liu, P., Sohn, H., & Pay'a, J. (2019). Fundamentals of Nonlinear Acoustical Techniques and Sideband Peak Count. In Nonlinear Ultrasonic and Vibro-Acoustical Techniques for Nondestructive Evaluation(pp 1--88). Springer, Cham.
• Li, W., & Kundu, T. (2018). Nondestructive Evaluation (NDE) of Materials and Structures from Production to Retirement. In Advances in Manufacturing and Processing of Materials and Structures(pp 463--496). CRC Press.
• Ahmad, R., & Kundu, T. (2013). Influence of water flow through pipe networks for damage detection using guided waves. In Nondestructive Testing of Materials and Structures(pp 681--687). Springer, Dordrecht.
• Kundu, T. (2013). Guided waves for nondestructive testing--experiment and analysis. In Nondestructive Testing of Materials and Structures(pp 567--576). Springer, Dordrecht.
• Kundu, T., & Placko, D. (2003). Modeling of Ultrasonic Field by Distributed Point Source Method. In Ultrasonic Nondestructive Evaluation(pp 157--216). CRC Press.
• Bereiter-Hahn, J., Blase, C., Kundu, T., & Wagner, O. (2002). Cells as seen with the acoustic microscope. In Acoustical Imaging(pp 83--90). Springer, Boston, MA.
• Kundu, T., & Jorgensen, C. (2000). Acoustic microscopy for bone characterization. In American Society of Mechanical Engineers (Publication) NDE.
• Na, W. B., Kundu, T., & Ehsani, M. R. (2000). Inspection of concrete-metal rod interface using guided waves. In American Society of Mechanical Engineers, Applied Mechanics Division, AMD.
• Guo, D., & Kundu, T. (1999). Special sensors for generating Lamb waves in pipes. In Review of Progress in Quantitative Nondestructive Evaluation(pp 1155--1162). Springer, Boston, MA.
• Karpur, P., Kundu, T., & Ditri, J. J. (1999). Adhesive Joint Evaluation Using Lamb Wave Modes with Appropriate Displacement, Stress, and Energy Distribution Profiles. In Review of Progress in Quantitative Nondestructive Evaluation(pp 1533--1542). Springer, Boston, MA.
• Kundu, T., Ehsani, M., Guo, D., & Maslov, K. I. (1999). Composite-concrete interface characterization by lamb waves. In Review of Progress in Quantitative Nondestructive Evaluation(pp 1911--1918). Springer, Boston, MA.
• Hosten, B., Castaings, M., & Kundu, T. (1998). Identification of viscoelastic moduli of composite materials from the plate transmission coefficients. In Review of progress in quantitative Nondestructive Evaluation(pp 1117--1124). Springer, Boston, MA.
• Jung, Y. C., Kundu, T., & Ehsani, M. (1997). Lamb wave inspection of concrete beams. In American Society of Mechanical Engineers (Publication) NDE.
• Kundu, T., Karpur, P., Matikas, T. E., & Nicolaou, P. D. (1996). Lamb wave mode sensitivity to detect various material defects in multilayered composite plates. In Review of Progress in Quantitative Nondestructive Evaluation(pp 231--238). Springer, Boston, MA.
• Maslov, K. I., Kundu, T., & Ghosh, T. (1996). A New Technique for Surface Acoustic Wave Speed Measurement in Laterally Inhomogeneous Materials. In Review of Progress in Quantitative Nondestructive Evaluation(pp 2007--2014). Springer, Boston, MA.
• Maslov, K. I., Kundu, T., & Lobkis, O. I. (1996). A new technique for distinguishing internal voids from solid inclusions. In Review of Progress in Quantitative Nondestructive Evaluation(pp 883--890). Springer, Boston, MA.
• Benson, D. M., Karpur, P., Matikas, T. E., & Kundu, T. (1995). Experimental generation of Lamb wave dispersion using Fourier analysis of leaky modes. In Review of Progress in Quantitative Nondestructive Evaluation(pp 187--194). Springer, Boston, MA.
• Isakson, S., Meyyappan, A., & Wade, G. (1995). When A-Priori Information Cannot Resolve Tomogram Ambiguities. In Acoustical Imaging(pp 565--572). Springer, Boston, MA.
• Lobkis, O. I., Maslov, K. I., Kundu, T., & Zinin, P. V. (1995). An Improved Ultrasonic Technique for Three Dimensional Inclusions. In Review of Progress in Quantitative Nondestructive Evaluation(pp 123--130). Springer, Boston, MA.
• Lobkis, O., Kundu, T., & Zinin, P. (1995). Acoustic microscopy for spherical cavities in solids. In Acoustical Imaging(pp 573--580). Springer, Boston, MA.
• Yang, W., & Kundu, T. (1995). Lamb wave propagation in multilayered anisotropic solids and its application towards imaging material defects. In Acoustical Imaging(pp 23--30). Springer, Boston, MA.
• Kundu, T., Awal, M. A., & Mahalanobis, A. (1992). Acoustic Microscopy for Material Characterization. In Acoustical Imaging(pp 673--677). Springer, Boston, MA.
• Kundu, T., & Awal, M. A. (1988). Dynamic Response of Cracks Intersecting the Interface of a Two Layered Plate. In Computational Mechanics’ 88(pp 355--358). Springer, Berlin, Heidelberg.
• Mal, A. K., & Kundu, T. (1987). Reflection of bounded acoustic beams from a layered solid. In Review of Progress in Quantitative Nondestructive Evaluation(pp 109--116). Springer, Boston, MA.
• Mal, A. K., Kundu, T., & Xu, P. C. (1984). ON THE SURFACE RESPONSE OF A MULTILAYERED SOLID TO A DISLOCATION SOURCE.. In American Society of Mechanical Engineers, Pressure Vessels and Piping Division (Publication) PVP. ASME (AMD-v 60).

Journals/Publications

• Alnuaimi, H., Amjad, U., & Kundu, T. (2024). Acoustic source localization in composite plates using Sideband Peak Count--Index technique. Ultrasonics, 107273.
• Alnuaimi, H., Amjad, U., Sen, N., & Kundu, T. (2024). A Note on Performance Assessment of Signal Energy-Based Acoustic Source Localization in a Carbon Fiber-Reinforced Polymer Plate. Journal of Nondestructive Evaluation, Diagnostics and Prognostics of Engineering Systems, 1--13.
• Dai, Z., Liu, J., Geng, H., Cui, Z., & Kundu, T. (2024). The influence of slip boundary effect on the propagation of shear horizontal guided waves in a fluid-saturated porous medium. Journal of Engineering Mathematics, 144(1), 1--14.
• Hou, H., Zhang, G., Song, Y., Li, X., Zhang, S., & Kundu, T. (2024). Measurement of frequency-dependent shear wave attenuation coefficients using an oblique incidence pulse-echo ultrasonic method. Measurement, 114298.
• Thakur, A., Kalimullah, N. M., Shelke, A., Hazra, B., & Kundu, T. (2024). NG-DPSM: A neural green-distributed point source method for modelling ultrasonic field emission near fluid-solid interface using physics informed neural network. Engineering Applications of Artificial Intelligence, 131, 107828.
• Zhang, G., Hu, B. o., Alnuaimi, H., Amjad, U., & Kundu, T. (2024). Numerical modeling with experimental verification investigating the effect of various nonlinearities on the sideband peak count-index technique. Ultrasonics, 107259.
• Zhang, G., Li, X., Li, T., & Kundu, T. (2024). Ordinary state-based peri-ultrasound modeling for monitoring crack propagation in plate structures using sideband peak count-index technique. Journal of Sound and Vibration, 568, 117962.
• Zhou, Z., Cui, Z., Liu, J., & Kundu, T. (2024). A health monitoring technique for spherical structures based on multi-acoustic source localization. Structural Health Monitoring, 14759217231220063.
• Alnuaimi, H. N., Amjad, U., Russo, P., Lopresto, V., & Kundu, T. (2023). Advanced non-linear ultrasonic sideband peak count-index technique for efficient detection and monitoring of defects in composite plates. Journal of Vibration and Control, 10775463231168228.
• Amjad, U., Ghimire, U., Alnuaimi, H., Bheemasetti, T., & Kundu, T. (2023). Monitoring of Phase Transition in Frozen Soil Using the Nonlinear (SPC-1) Ultrasonic Technique. STRUCTURAL HEALTH MONITORING 2023.
• Castellano, A., Fraddosio, A., Paparella, F., Piccioni, M. D., & Kundu, T. (2023). The evaluation of the adhesion defects in FRCM reinforcements for masonry constructions by Sideband Peak Count based nonlinear acoustic technique. Journal of Vibration and Control, 10775463231187456.
• Geng, H., Ding, H., Liu, J., Cui, Z., & Kundu, T. (2023). Reflection and Refraction of Plane Waves at an Interface of Water and Porous Media with Slip Boundary Effect. Transport in Porous Media, 1--18.
• Li, X., Li, T., & Kundu, T. (2023). Monitoring Elastoplastic Deformation in Ductile Metallic Materials Using Sideband Peak Count-Index Technique.
• Liu, J., Li, Z., Cui, Z., Fu, L., & Kundu, T. (2023). Effect of axial stresses on longitudinal guided waves in a fluid-filled pipe. The Journal of the Acoustical Society of America, 153(3), 1612--1622.
• Liu, J., Liu, J., Cui, Z., & Kundu, T. (2023). Wavefields in a cased hole surrounded by a formation with transverse isotropy caused by axial stresses. Geomechanics and Geophysics for Geo-Energy and Geo-Resources, 9(1), 61.
• Liu, P., Yang, L., Yi, K., Kundu, T., & Sohn, H. (2023). Application of nonlinear ultrasonic analysis for in situ monitoring of metal additive manufacturing. Structural Health Monitoring, 22(3), 1760--1775.
• Ma, C., Zhou, Z., Liu, J., Cui, Z., & Kundu, T. (2023). Acoustic source localization using L-shaped sensor clusters: a review. Ultrasonics, 107020.
• Park, S., & Kundu, T. (2023). A modified sideband peak count based nonlinear ultrasonic technique for material characterization. Ultrasonics, 128, 106858.
• Sagar, R. V., Saha, I., Basu, D. J., & Kundu, T. (2023). Statistics of acoustic emission waveforms in characterizing the fracture process zone in fibre-reinforced cementitious materials under mode I fracture. Structural Health Monitoring, 14759217231196216.
• Sasmal, S., Basu, S., Himakar, C. V., & Kundu, T. (2023). Detection of interface flaws in Concrete-FRP composite structures using linear and nonlinear ultrasonics based techniques. Ultrasonics, 132, 107007.
• Wang, M., Pau, A., Zhang, G., & Kundu, T. (2023). Monitoring prestress in plates by sideband peak count-index (SPC-I) and nonlinear higher harmonics techniques.
• Yin, S., Xiao, H., Xu, C., Deng, M., & Kundu, T. (2023). Theoretical error formation and evaluation of acoustic source localization for cluster-based techniques. Ultrasonics, 132, 106982.
• Zhang, G., Li, X., & Kundu, T. (2023). Ordinary state-based peri-ultrasound modeling to study the effects of multiple cracks on the nonlinear response of plate structures. Ultrasonics, 133, 107028.
• Zhang, G., Li, X., Li, T., & Kundu, T. (2023). Monitoring elastoplastic deformation in ductile metallic materials using sideband peak count-index (SPC-I) technique. Journal of Nondestructive Evaluation, Diagnostics and Prognostics of Engineering Systems, 1--15.
• Zhou, J., Cui, Z., Zhang, B., Kundu, T., & Sevostianov, I. (2023). The effect of porosity on the elastic properties of cortical bone and ultrasound propagation. International Journal of Engineering Science, 182, 103772.
• Zhou, Z., Cui, Z., Liu, J., & Kundu, T. (2023). A rapid technique for detecting and localizing damage in composite laminates. Engineering Fracture Mechanics, 277, 108995.
• Zhou, Z., Liu, J., Cui, Z., & Kundu, T. (2023). A rapid localization technique for detecting multiple damages in plate-like structures with unknown material properties. Mechanical Systems and Signal Processing, 199, 110479.
• Alnuaimi, H., Amjad, U., Park, S., Russo, P., Lopresto, V., & Kundu, T. (2022). An improved nonlinear ultrasonic technique for detecting and monitoring impact induced damage in composite plates. Ultrasonics, 119, 106620.
• Arumaikani, T., Sasmal, S., & Kundu, T. (2022). Detection of initiation of corrosion induced damage in concrete structures using nonlinear ultrasonic techniques. The Journal of the Acoustical Society of America, 151(2), 1341--1352.
• Boffa, N. D., Arena, M., Monaco, E., Viscardi, M., Ricci, F., & Kundu, T. (2022). About the combination of high and low frequency methods for impact detection on aerospace components. Progress in Aerospace Sciences, 129, 100789.
• Hu, B. o., & Kundu, T. (2022). Seismic Performance Evaluation of Precast Prestressed Concrete Frames Containing Recycled Aggregates. ACI Structural Journal, 119(3), 291--305.
• Liu, P., Yang, L., Yi, K., Kundu, T., & Sohn, H. (2022). Application of nonlinear ultrasonic analysis for in situ monitoring of metal additive manufacturing. Structural Health Monitoring, 14759217221113447.
• Nikvar-Hassani, A., Alnuaimi, H. N., Amjad, U., Sasmal, S., Zhang, L., & Kundu, T. (2022). Alkali Activated Fly Ash-Based Concrete: Evaluation of Curing Process Using Non-Linear Ultrasonic Approach. Journal of Nondestructive Evaluation, Diagnostics and Prognostics of Engineering Systems, 5(2), 021006.
• Nikvar-Hassani, A., Alnuaimi, H. N., Amjad, U., Sasmal, S., Zhang, L., & Kundu, T. (2022). Alkali Activated Fly Ash-Based Concrete: Evaluation of Curing Process Using Non-Linear Ultrasonic Approach. Journal of Nondestructive Evaluation, Diagnostics and Prognostics of Engineering Systems, 5(2).
• Park, S., Alnuaimi, H., Hayes, A., Sitkiewicz, M., Amjad, U., Muralidharan, K., & Kundu, T. (2022). Nonlinear acoustic technique for monitoring porosity in additively manufactured parts. Journal of Nondestructive Evaluation, Diagnostics and Prognostics of Engineering Systems, 5(2), 021008.
• Sen, N., & Kundu, T. (2022). A new signal energy-based approach to acoustic source localization in orthotropic plates: A numerical study. Mechanical Systems and Signal Processing, 171, 108843.
• Sen, N., Kundu, T., & Missoum, S. (2022). A note on the effect of material uncertainty on acoustic source localization error in anisotropic plates. Ultrasonics, 119, 106623.
• Wang, W., Gao, W., Liu, J., Cui, Z., & Kundu, T. (2022). Modelling and simulation of borehole seismoelectric response with an impermeable wall. The Journal of the Acoustical Society of America, 152(2), 765--775.
• Wang, W., Gao, W., Liu, J., Kundu, T., & Cui, Z. (2022). The Response Mechanism of Borehole Shear-Horizontal Transverse-Electric Seismoelectric Waves to Fluid Salinity. Applied Sciences, 12(10), 5132.
• Yin, S., Xiao, H., Xu, C., Wang, J., Deng, M., & Kundu, T. (2022). Microcrack localization using nonlinear Lamb waves and cross-shaped sensor clusters. Ultrasonics, 106770.
• Yin, S., Xiao, H., Xu, C., Wang, J., Deng, M., & Kundu, T. (2022). Microcrack localization using nonlinear Lamb waves and cross-shaped sensor clusters. Ultrasonics, 124, 106770.
• Zhang, G., Li, X., Zhang, S., & Kundu, T. (2022). Sideband peak count-index technique for monitoring multiple cracks in plate structures using ordinary state-based peri-ultrasound theory. The Journal of the Acoustical Society of America, 152(5), 3035--3048.
• Zhang, S., Cheng, C., Li, X., & Kundu, T. (2022). Fast Fourier transform method for determining velocities of ultrasonic Rayleigh waves using a comb transducer. Ultrasonics, 124, 106754.
• Zhou, Z., Cui, Z., & Kundu, T. (2022). A fast approach for acoustic source localization on a thin spherical shell. Structural Health Monitoring, 21(4), 1723--1737.
• Zhou, Z., Cui, Z., Yin, S., & Kundu, T. (2022). A rapid acoustic source localization technique for early warning of building material damage. Construction and Building Materials, 325, 126840.
• ALNUAIMI, H., AMJAD, U., PARK, S., RUSSO, P., LOPRESTO, V., & KUNDU, T. (2021). Robust Detection of Damage in Composite Plates Using the Nonlinear SPC-I Ultrasonic Technique. STRUCTURAL HEALTH MONITORING 2021.
• Alnuaimi, H. N., Sasmal, S., Amjad, U., Nikvar-Hassani, A., Zhang, L., & Kundu, T. (2021). Monitoring Concrete Curing by Linear and Nonlinear Ultrasonic Methods.. ACI Materials Journal, 118(3).
• Alnuaimi, H., Amjad, U., Russo, P., Lopresto, V., & Kundu, T. (2021). Monitoring damage in composite plates from crack initiation to macro-crack propagation combining linear and nonlinear ultrasonic techniques. Structural Health Monitoring, 20(1), 139--150.
• Basu, S., Thirumalaiselvi, A., Sasmal, S., & Kundu, T. (2021). Nonlinear ultrasonics-based technique for monitoring damage progression in reinforced concrete structures. Ultrasonics, 115, 106472.
• Castellano, A., Fraddosio, A., Piccioni, M. D., & Kundu, T. (2021). Linear and nonlinear ultrasonic techniques for monitoring stress-induced damages in concrete. Journal of Nondestructive Evaluation, Diagnostics and Prognostics of Engineering Systems, 4(4), 041001.
• Castellano, A., Fraddosio, A., Piccioni, M. D., & Kundu, T. (2021). Linear and nonlinear ultrasonic techniques for monitoring stress-induced damages in concrete. Journal of Nondestructive Evaluation, Diagnostics and Prognostics of Engineering Systems, 4(4).
• Fu, J., Yin, S., Cui, Z., & Kundu, T. (2021). Experimental research on rapid localization of acoustic source in a cylindrical shell structure without knowledge of the velocity profile. Sensors, 21(2), 511.
• Kundu, T., Reis, H., & Georgeson, G. (2021). The 47th Review of Progress in Quantitative Nondestructive Evaluation (QNDE 2020). Journal of Nondestructive Evaluation, Diagnostics and Prognostics of Engineering Systems, 4(4), 040201.
• Kundu, T., Reis, H., Ihn, J. B., & Dzenis, Y. (2021). WELCOME to QNDE 2021. Proceedings of 2021 48th Annual Review of Progress in Quantitative Nondestructive Evaluation, QNDE 2021.
• Sen, N., Gawro\'nski, M., Packo, P., Uhl, T., & Kundu, T. (2021). Square-shaped sensor clusters for acoustic source localization in anisotropic plates by wave front shape-based approach. Mechanical Systems and Signal Processing, 153, 107489.
• Wang, W., Cui, Z., Liu, J., & Kundu, T. (2021). Dependence of borehole shear-horizontal-wave seismoelectric response on soil textures. Geophysical Prospecting, 69(1), 250--266.
• Yin, S., Xiao, H., Cui, Z., & Kundu, T. (2021). Rapid localization of acoustic source using sensor clusters in 3D homogeneous and heterogeneous structures. Structural health monitoring, 20(3), 1145--1155.
• Zhang, G., Li, X., Zhang, S., & Kundu, T. (2021). Investigation of frequency-dependent attenuation coefficients for multiple solids using a reliable pulse-echo ultrasonic measurement technique. Measurement, 177, 109270.
• Agarwal, V., Shelke, A., Ahluwalia, B. S., Melands\o, F., Kundu, T., & Habib, A. (2020). Damage localization in piezo-ceramic using ultrasonic waves excited by dual point contact excitation and detection scheme. Ultrasonics, 108, 106113.
• Hu, B. o., & Kundu, T. (2020). Seismic Testing and Numerical Analysis of Beam-Column Knee Joints in Recycled-Aggregate Concrete Frames.. ACI Structural Journal, 117(1).
• Sen, N., & Kundu, T. (2020). Acoustic source localization in a highly anisotropic plate with unknown orientation of its axes of symmetry and material properties with numerical verification. Ultrasonics, 100, 105977.
• Taskhiri, M. S., Hafezi, M. H., Harle, R., Williams, D., Kundu, T., & Turner, P. (2020). Ultrasonic and thermal testing to non-destructively identify internal defects in plantation eucalypts. Computers and electronics in agriculture, 173, 105396.
• Alnuaimi, H., Amjad, U., Russo, P., Lopresto, V., & Kundu, T. (2019). Linear and non-linear analysis of composite plates using guided acoustic waves. HEALTH MONITORING OF STRUCTURAL AND BIOLOGICAL SYSTEMS XIII, 10972.
• Banerjee, S., & Kundu, T. (2019). Sensing & Measurement Modeling ultrasonic wave scattering by internal anomalies for structural monitoring.
• Eiras, J. N., Gaona, F., Monz'o, J., Kundu, T., Popovics, J. S., Pay'a, J., & Bonilla, M. (2019). Caracterizaci'on de GRC y evaluaci'on del proceso de envejecimiento por medio del an'alisis de espectros de vibraci'on.
• Fooladi, S., & Kundu, T. (2019). Distributed point source modeling of the scattering of elastic waves by a circular cavity in an anisotropic half-space. ULTRASONICS, 94, 264-280.
• Hu, B. o., & Kundu, T. (2019). Seismic Performance of Interior and Exterior Beam-Column Joints in Recycled Aggregate Concrete Frames. JOURNAL OF STRUCTURAL ENGINEERING, 145(3).
• Hu, B. o., Lv, H., & Kundu, T. (2019). Experimental study on seismic behavior of reinforced concrete frame in primary and middle schools with different strengthening methods. CONSTRUCTION AND BUILDING MATERIALS, 217, 473-486.
• Hu, B. o., Wei, X., Lv, H., Kundu, T., & Li, N. (2019). Experimental and Analytical Study on Seismic Behavior of Strengthened Existing Single Frame Structures with Exterior Cantilevers. ADVANCES IN MATERIALS SCIENCE AND ENGINEERING.
• Karpuq, P., Benson, D. M., Matikas, T. E., & Kundu, T. (2019). An Approoch to Determine the Experi me ntol Trq nsm itter-Receiver Geomefry for the Reception.
• Kiousis, P. D. (2019). Constitutive Laws for Engineering Materials. Theory and Applications.
• Kundu, T. (2019). An improved technique for elastodynamic Green’s function computation for transversely isotropic solids. ASME Journal of Nondestructive Evaluation, Diagnostics and Prognostics of Engineering Systems, 2(2), 021005-1 to 021005-7.
  More info

  Fooladi, S. and T. Kundu, “An improved technique for elastodynamic Green’s function computation for transversely isotropic solids”, ASME Journal of Nondestructive Evaluation, Diagnostics and Prognostics of Engineering Systems, Vol. 2(2), pp. 021005-1 to 021005-7, 2019. Winner of the Second Best Paper of the journal.
• Kundu, T., & Placko, D. (2019). Ultrasonic Field Modeling in Multilayered Fluid Structures Using the Distributed Point Source Method Technique.
• Liu, J., Zhou, Y., Cui, Z., & Kundu, T. (2019). Multipole borehole acoustic field in a transversely isotropic medium induced by stress. JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA, 146(2), 1290-1301.
• Niu, X., Ore, E., Glinka, G., Durban, D., Gibson, G. P., Kujawski, D., Druce, S. G., Ellyin, E., Theocaris, P. S., Karim, M. R., Makrakis, G., Kundu, T., Petroski, H. J., McCartney, L. N., Ojdrovic, R. P., Ohta, A., Kundu, T., Kosuge, M., Matsuoka, S., , Hassan, T., et al. (2019). The following papers have been accepted for publication and will appear in future issues of the.
• Sen, N., Gawronski, M., Packo, P., Uhl, T., & Kundu, T. (2019). Acoustic source localization in anisotropic plates without knowing their material properties: an experimental investigation. HEALTH MONITORING OF STRUCTURAL AND BIOLOGICAL SYSTEMS XIII, 10972.
• Vasiljevic, M., & Kundu, T. (2019). National Science Foundation; Grant No. CMS9901221: Development of Non-Contact Sensors for Pipe Inspection by Lamb Wave.
• Yanagita, T., & Kundu, T. (2019). National Science Foundation; Grant No. CMS9901221/CMMI0530991: Development of Non-Contact Sensors for Pipe Inspection by Lamb Wave.
• Yin, S., Cui, Z., & Kundu, T. (2019). Acoustic source localization in non-homogenous plates. HEALTH MONITORING OF STRUCTURAL AND BIOLOGICAL SYSTEMS XIII, 10972.
• Yin, S., Cui, Z., Fu, J., & Kundu, T. (2019). Acoustic source localization in heterogeneous media. ULTRASONICS, 99.
• Amjad, U., Blase, C., Alnuaimi, H. N., Dao, C. M., Bereiter-Hahn, J., & Kundu, T. (2018). Effects of transducers on guided wave based structural health monitoring. HEALTH MONITORING OF STRUCTURAL AND BIOLOGICAL SYSTEMS XII, 10600.
• Blase, C., Amjad, U., Kundu, T., Bereiter-Hahn, J., Blume, M., & Sader, R. (2018). Characterization of dental tissue by reflection and transmission ultrasound microscopy. HEALTH MONITORING OF STRUCTURAL AND BIOLOGICAL SYSTEMS XII, 10600.
• Boffa, N. D., Monaco, E., Maio, L., Memmolo, V., Ricci, F., Mendoza, E., & Kundu, T. (2018). Hybrid guided wave based SHM system for composite structures for impact and delamination detection combining fiber Bragg grating sensing and piezoelectric patches.. HEALTH MONITORING OF STRUCTURAL AND BIOLOGICAL SYSTEMS XII, 10600.
• Hafezi, M. H., & Kundu, T. (2018). Peri-ultrasound modeling for surface wave propagation. Ultrasonics, 84, 162--171.
• Hafezi, M. H., & Kundu, T. (2018). Peri-ultrasound modeling of dynamic response of an interface crack showing wave scattering and crack propagation. Journal of Nondestructive Evaluation, Diagnostics and Prognostics of Engineering Systems, 1(1), 011003.
• Kundu, T. (2018). Introduction to the Inaugural Issue of the Journal of Nondestructive Evaluation, Diagnostics, and Prognostics of Engineering Systems. Journal of Nondestructive Evaluation, Diagnostics and Prognostics of Engineering Systems, 1(1), 010201.
• Sen, N., & Kundu, T. (2018). A new wave front shape-based approach for acoustic source localization in an anisotropic plate without knowing its material properties. Ultrasonics, 87, 20--32.
• Taskhiri, M. S., Hafezi, M. H., Turner, P., & Kundu, T. (2018). Non-destructive evaluation of a plantation eucalypts. HEALTH MONITORING OF STRUCTURAL AND BIOLOGICAL SYSTEMS XII, 10600.
• Yin, S., Cui, Z., & Kundu, T. (2018). Acoustic source localization in anisotropic plates with “Z” shaped sensor clusters. Ultrasonics, 84, 34--37.
• Ding, H., Liu, J., Cui, Z., & Kundu, T. (2017). Seismoelectric wave propagation modeling in a borehole in water-saturated porous medium having an electrochemical interface. Chinese Physics B, 26(12), 124301.
• Fooladi, S., & Kundu, T. (2017). Application of Distributed Point Source Method (DPSM) to wave propagation in anisotropic media. HEALTH MONITORING OF STRUCTURAL AND BIOLOGICAL SYSTEMS 2017, 10170.
• Fooladi, S., & Kundu, T. (2017). Ultrasonic field modeling in anisotropic materials by distributed point source method. ULTRASONICS, 78, 115-124.
• Hafezi, M. H., Alebrahim, R., & Kundu, T. (2017). Peri-ultrasound for modeling linear and nonlinear ultrasonic response. Ultrasonics, 80, 47--57.
• Liu, J., Cui, Z., Wang, K., & Kundu, T. (2017). Determining maximum shear stress in confined substrate from elastic wave reflection coefficient. Science China Earth Sciences, 1--12.
• Park, W. H., Packo, P., & Kundu, T. (2017). Acoustic source localization in an anisotropic plate without knowing its material properties--a new approach. Ultrasonics.
• Amjad, U., Yadav, S. K., & Kundu, T. (2016). Detection and quantification of delamination in laminated plates from the phase of appropriate guided wave modes. Optical Engineering, 55(1), 011006--011006.
• Eiras, J. N., Kundu, T., Popovics, J. S., Monz'o, J., Borrachero, M. V., & Pay'a, J. (2016). Effect of carbonation on the linear and nonlinear dynamic properties of cement-based materials. Optical Engineering, 55(1), 011004--011004.
• Grabowski, K., Gawronski, M., Baran, I., Spychalski, W., Staszewski, W. J., Uhl, T., Kundu, T., & Packo, P. (2016). Time--distance domain transformation for Acoustic Emission source localization in thin metallic plates. Ultrasonics, 68, 142--149.
• Kundu, T., Scalea, F. L., & Sohn, H. (2016). Special Section Guest Editorial: Structural Health Monitoring: Use of Guided Waves and/or Nonlinear Acoustic Techniques. Optical Engineering, 55(1), 011001--011001.
• Placko, D., Bore, T., & Kundu, T. (2016). Family of Quantum Sources for Improving Near Field Accuracy in Transducer Modeling by the Distributed Point Source Method. Applied Sciences, 6(10), 302.
• Zhao, J., Bao, T., & Kundu, T. (2016). Wide range fiber displacement sensor based on bending loss. Journal of Sensors, 2016.
• Zhao, J., Bao, T., Chen, S., & Kundu, T. (2016). Smart aggregate-piezoceramic patch combination for health monitoring of concrete structures. Journal of Sensors, 2016.
• Amjad, U., Yadav, S. K., & Kundu, T. (2015). Detection and quantification of diameter reduction due to corrosion in reinforcing steel bars. Structural Health Monitoring, 14(5), 532--543.
• Amjad, U., Yadav, S. K., & Kundu, T. (2015). Detection and quantification of pipe damage from change in time of flight and phase. Ultrasonics, 62, 223--236.
• Genov'es, V., Riestra, C., Borrachero, M. V., Eiras, J., Kundu, T., & Pay'a, J. (2015). Multimodal analysis of GRC ageing process using nonlinear impact resonance acoustic spectroscopy. Composites Part B: Engineering, 76, 105--111.
• Habib, A., Shelke, A., Vogel, M., Brand, S., Jiang, X., Pietsch, U., Banerjee, S., & Kundu, T. (2015). Quantitative Ultrasonic Characterization of c-axis oriented polycrystalline AlN thin film for smart device application. Acta Acustica united with Acustica, 101(4), 675--683.
• Kundu, T., Yang, X., Nakatani, H., & Takeda, N. (2015). A two-step hybrid technique for accurately localizing acoustic source in anisotropic structures without knowing their material properties. Ultrasonics, 56, 271--278.
• Liu, P., Sohn, H., Yang, S., & Kundu, T. (2015). Fatigue crack localization using noncontact laser ultrasonics and state space attractors. The Journal of the Acoustical Society of America, 138(2), 890--898.
• Zhao, J., Bao, T., Chen, S., & Kundu, T. (2015). Smart aggregate-piezoceramic patch combination for health monitoring of concrete structures. Journal of Sensors, 2016.
• Eiras, J. N., Monz'o, J., Pay'a, J., Kundu, T., & Popovics, J. S. (2014). Non-classical nonlinear feature extraction from standard resonance vibration data for damage detection. The Journal of the Acoustical Society of America, 135(2), EL82--EL87.
• Eiras, J. N., Monzo, J., Paya, J., Kundu, T., & Popovics, J. S. (2014). Non-classical nonlinear feature extraction from standard resonance vibration data for damage detection. JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA, 135(2), EL82-EL87.
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  Dynamic non-classical nonlinear analyses show promise for improved damage diagnostics in materials that exhibit such structure at the mesoscale, such as concrete. In this study, nonlinear non-classical dynamic material behavior from standard vibration test data, using pristine and frost damaged cement mortar bar samples, is extracted and quantified. The procedure is robust and easy to apply. The results demonstrate that the extracted nonlinear non-classical parameters show expected sensitivity to internal damage and are more sensitive to changes owing to internal damage levels than standard linear vibration parameters. (C) 2014 Acoustical Society of America
• Kundu, T. (2014). Acoustic source localization. ULTRASONICS, 54(1), 25-38.
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  In this article different techniques for localizing acoustic sources are described and the advantages/disadvantages of these techniques are discussed. Some source localization techniques are restricted to isotropic structures while other methods can be applied to anisotropic structures as well. Some techniques require precise knowledge of the direction dependent velocity profiles in the anisotropic body while other techniques do not require that knowledge. Some methods require accurate values of the time of arrival of the acoustic waves at the receivers while other techniques can function without that information. Published papers introducing various techniques emphasize the advantages of the introduced techniques while ignoring and often not mentioning the limitations and weaknesses of the new techniques. What is lacking in the literature is a comprehensive review and comparison of the available techniques; this article attempts to do that. After reviewing various techniques the paper concludes which source localization technique should be most effective for what type of structure and what the current research needs are. (C) 2013 Elsevier B. V. All rights reserved.
• Kundu, T. (2014). Acoustic source localization. Ultrasonics, 54(1), 25--38.
• Kundu, T. (2014). Ultrasonic and electromagnetic waves for nondestructive evaluation and structural health monitoring. Procedia Engineering, 86, 395--405.
• Kundu, T., & Kundu, T. -. (2014). Acoustic source localization. Ultrasonics, 54(1).
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  In this article different techniques for localizing acoustic sources are described and the advantages/disadvantages of these techniques are discussed. Some source localization techniques are restricted to isotropic structures while other methods can be applied to anisotropic structures as well. Some techniques require precise knowledge of the direction dependent velocity profiles in the anisotropic body while other techniques do not require that knowledge. Some methods require accurate values of the time of arrival of the acoustic waves at the receivers while other techniques can function without that information. Published papers introducing various techniques emphasize the advantages of the introduced techniques while ignoring and often not mentioning the limitations and weaknesses of the new techniques. What is lacking in the literature is a comprehensive review and comparison of the available techniques; this article attempts to do that. After reviewing various techniques the paper concludes which source localization technique should be most effective for what type of structure and what the current research needs are.
• Liu, P., Sohn, H., & Kundu, T. (2014). Fatigue crack localization using laser nonlinear wave modulation spectroscopy (LNWMS). J. Korean Soc. Nondestruct. Test., 36, 419--427.
• Liu, P., Sohn, H., & Kundu, T. (2014). Fatigue crack localization using laser nonlinear wave modulation spectroscopy (LNWMS). Journal of the Korean Society for Nondestructive Testing, 34(6), 419--427.
• Liu, P., Sohn, H., Kundu, T., & Yang, S. (2014). Noncontact detection of fatigue cracks by laser nonlinear wave modulation spectroscopy (LNWMS). NDT & E INTERNATIONAL, 66, 106-116.
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  Nonlinear wave modulation spectroscopy (NWMS) has been used to detect nonlinear ultrasonic signatures produced by fatigue cracks in materials. It is done by generating ultrasonic waves at two different frequencies and measuring their modulation. A proper choice of two distinct frequencies for a given structure plays a significant role in NWMS. This paper, instead of using input signals at two distinct frequencies, takes only one broadband pulse signal as the driving input, which can be generated by a laser beam. With a broadband excitation, material nonlinearity exhibits modulation at multiple peaks in a spectral plot due to interactions among various input frequency components of the broadband input. A feature called sideband peak count (SPC), which is defined as the ratio of the number of sideband (modulation) peaks over a moving threshold to the total peak number in the specified frequency band, is extracted from the spectral plot to measure the degree of material nonlinearity. The basic premise of the proposed laser nonlinear wave modulation spectroscopy (LNWMS) is that this SPC value will rise as the level of material nonlinearity increases. A noncontact laser ultrasonic system has been built for LNWMS measurement by integrating and synchronizing a Q-switched Nd:YAG laser for ultrasonic wave generation and a laser Doppler vibrometer for ultrasonic wave detection. The proposed LNWMS technique has been successfully tested for detecting fatigue cracks in metallic plates and aircraft fitting-lugs having complex geometries. (C) 2014 Elsevier Ltd. All rights reserved.
• Liu, P., Sohn, H., Kundu, T., & Yang, S. (2014). Noncontact detection of fatigue cracks by laser nonlinear wave modulation spectroscopy (LNWMS). NDT & E International, 66, 106--116.
• Nakatani, H., Kundu, T., & Takeda, N. (2014). Improving accuracy of acoustic source localization in anisotropic plates. ULTRASONICS, 54(7), 1776-1788.
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  The acoustic source localization technique for anisotropic plates proposed by the authors in an earlier publication ([1] Kundu et al., 2012) is improved in this paper by adopting some modifications. The improvements are experimentally verified on anisotropic flat and curved composite plates. Difficulties associated with the original technique were first investigated before making any modification. It was noted that the accuracy of this technique depends strongly on the accuracy of the measured time difference of arrivals (TDOA) at different receiving sensors placed in close proximity in a sensor cluster. The sensor cluster is-needed to obtain the direction-of the acoustic source without knowing the material properties of the plate. Two modifications are proposed to obtain the accurate TDOA. The first one is to replace the recorded full time histories by only their initial parts - the first dip and peak - for the subsequent signal processing. The second modification is to place the sensors in the sensor cluster as close as possible. It is shown that the predictions are improved significantly with these modifications. These modifications are then applied to another sensor cluster based technique called the beamforming technique, to see if similar improvements are achieved for that technique also with these modifications. (C) 2014 Elsevier B.V. All rights reserved.
• Nakatani, H., Kundu, T., & Takeda, N. (2014). Improving accuracy of acoustic source localization in anisotropic plates. Ultrasonics, 54(7), 1776--1788.
• Nakatani, H., Kundu, T., & Takeda, N. (2014). Improving accuracy of acoustic source localization in anisotropic plates. Ultrasonics.
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  Abstract: The acoustic source localization technique for anisotropic plates proposed by the authors in an earlier publication ([1] Kundu et al., 2012) is improved in this paper by adopting some modifications. The improvements are experimentally verified on anisotropic flat and curved composite plates. Difficulties associated with the original technique were first investigated before making any modification. It was noted that the accuracy of this technique depends strongly on the accuracy of the measured time difference of arrivals (TDOA) at different receiving sensors placed in close proximity in a sensor cluster. The sensor cluster is needed to obtain the direction of the acoustic source without knowing the material properties of the plate. Two modifications are proposed to obtain the accurate TDOA. The first one is to replace the recorded full time histories by only their initial parts - the first dip and peak - for the subsequent signal processing. The second modification is to place the sensors in the sensor cluster as close as possible. It is shown that the predictions are improved significantly with these modifications. These modifications are then applied to another sensor cluster based technique called the beamforming technique, to see if similar improvements are achieved for that technique also with these modifications. © 2014 Elsevier B.V. All rights reserved.
• Shelke, A., Banerjee, S., Habib, A., Rahani, E. K., Ahmed, R., & Kundu, T. (2014). Wave guiding and wave modulation using phononic crystal defects. JOURNAL OF INTELLIGENT MATERIAL SYSTEMS AND STRUCTURES, 25(13), 1541-1552.
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  In this article, we address the effect of regular and irregular distribution of phononic lattices on acoustic wave and investigate wave bending and refraction phenomena for some specific patterns of phononic crystals consisting of a square array of polyvinylchloride cylindrical rods in air matrix using finite element model. Bucay et al. have demonstrated that for a given configuration, the striking acoustic beam angle varying between 20 degrees and 40 degrees at 14.1 kHz central frequency shows positive, negative, and zero angle refraction inside phononic crystal and exhibits beam splitting after exiting the phononic crystal. These results are used as the benchmark in this article to validate the proposed model. Transmission spectrum in the phononic crystal has been studied for complete acoustic band gap as well as for positive and negative dispersion bands at frequencies ranging from 1 to 18 kHz. Using this established theory, in this article, the acoustic beam propagation through irregular phononic crystal structures and waveguides are investigated. It can be seen that small irregularity produces significant change in the acoustic field. It is shown that with a localized defect, resonating cavity waveguide is formed in the proposed acoustic metamaterials.
• Shelke, A., Banerjee, S., Habib, A., Rahani, E. K., Ahmed, R., & Kundu, T. (2014). Wave guiding and wave modulation using phononic crystal defects. Journal of Intelligent Material Systems and Structures, 25(13), 1541--1552.
• Wada, Y., Kundu, T., & Nakamura, K. (2014). Mesh-free distributed point source method for modeling viscous fluid motion between disks vibrating at ultrasonic frequency. JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA, 136(2), 466-474.
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  The distributed point source method (DPSM) is extended to model wave propagation in viscous fluids. Appropriate estimation on attenuation and boundary layer formation due to fluid viscosity is necessary for the ultrasonic devices used for acoustic streaming or ultrasonic levitation. The equations for DPSM modeling in viscous fluids are derived in this paper by decomposing the linearized viscous fluid equations into two components-dilatational and rotational components. By considering complex P- and S-wave numbers, the acoustic fields in viscous fluids can be calculated following similar calculation steps that are used for wave propagation modeling in solids. From the calculations reported the precision of DPSM is found comparable to that of the finite element method (FEM) for a fundamental ultrasonic field problem. The particle velocity parallel to the two bounding surfaces of the viscous fluid layer between two rigid plates (one in motion and one stationary) is calculated. The finite element results agree well with the DPSM results that were generated faster than the transient FEM results. (C) 2014 Acoustical Society of America.
• Wada, Y., Kundu, T., & Nakamura, K. (2014). Mesh-free distributed point source method for modeling viscous fluid motion between disks vibrating at ultrasonic frequency. The Journal of the Acoustical Society of America, 136(2), 466--474.
• Amjad, U., Nguyen, C. H., Yadav, S. K., Mahmoudabadi, E., & Kundu, T. (2013). Change in time-of-flight of longitudinal (axisymmetric) wave modes due to lamination in steel pipes. Proceedings of SPIE - The International Society for Optical Engineering, 8695.
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  Abstract: Investigations with the aid of longitudinal guided waves in cylindrical structures have been regularly carried out for non-destructive evaluation (NDE) and structural health monitoring (SHM). While earlier works concentrated on the amplitude reduction of the propagating waves due to structural anomalies in this work the change in time-of-flight is investigated. Longitudinal (axisymmetric) modes are excited by a PZT (Lead Zirconate Titanate) transducer for detection of any fluctuation or change in the surface of a steel pipe. Propagating waves are analyzed after proper signal processing. To observe the small change in TOF due to lamination on the surface of a steel pipe, cross-correlation technique is used to attain a higher temporal resolution. The experimental technique is discussed and the obtained results are presented in this paper. © 2013 SPIE.
• Bo, H. u., Kundu, T., Grill, W., Liu, B., & Toufigh, V. (2013). Embedded piezoelectric sensors for health monitoring of concrete structures. ACI Materials Journal, 110(2), 149-158.
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  Abstract: This paper presents an experimental investigation for detecting defects in concrete structures using so-called "smart aggregates." The smart aggregates are small cylinders with piezoelectric patches inside that can be embedded in concrete structures and used as both actuators and sensors. Specimens with different types of defects such as notch, hole, and inclusion were used in this study. To evaluate the effectiveness of the smart aggregates for detecting real cracks in concrete structures, three-point bending tests were carried out on two reinforced concrete beams. The test results indicate that not only the passive defects (notch, hole, or inclusion) but also the real cracks in reinforced concrete structures can be detected by the smart aggregates. Sensitivities of different parameters (time-of-flight, energy content of the signals, wavelet packet decomposition-based damage index) for various defects were also investigated. Copyright © 2013, American Concrete Institute.
• Eiras, J. N., Amjad, U., Mahmoudabadi, E., Payá, J., Bonilla, M., & Kundu, T. (2013). Monitoring ageing of alkali resistant glass fiber reinforced cement (GRC) using guided ultrasonic waves. Proceedings of SPIE - The International Society for Optical Engineering, 8695.
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  Abstract: Glass fiber reinforced cement (GRC) is a Portland cement based composite with alkali resistant (AR) glass fibers. The main drawback of this material is the ageing of the reinforcing fibers with time and especially in presence of humidity in the environment. Until now only destructive methods have been used to evaluate the durability of GRC. In this study ultrasonic guided wave inspection of plate shaped specimens has been carried out. The results obtained here show that acoustic signatures are capable of discerning ageing in GRC. Therefore, the ultrasonic guided wave based inspection technique is a promising method for the nondestructive evaluation of the durability of the GRC. © 2013 SPIE.
• Eiras, J. N., Kundu, T., Bonilla, M., & Pay'a, J. (2013). Nondestructive monitoring of ageing of alkali resistant glass fiber reinforced cement (GRC). Journal of Nondestructive Evaluation, 32(3), 300--314.
• Eiras, J. N., Kundu, T., Bonilla, M., & Paya, J. (2013). Nondestructive Monitoring of Ageing of Alkali Resistant Glass Fiber Reinforced Cement (GRC). JOURNAL OF NONDESTRUCTIVE EVALUATION, 32(3), 300-314.
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  Glass fiber reinforced cement (GRC) is a composite material made of portland cement mortar and alkali resistant (AR) fibers. AR fibers are added to portland cement to give the material additional flexural strength and toughness. However, ageing deteriorates the fibers and as a result the improvement in the mechanical properties resulted from the fiber addition disappears as the structure becomes old. The aim of this paper is monitoring GRC ageing by nondestructive evaluation (NDE) techniques. Two different NDE techniques-(1) nonlinear impact resonant acoustic spectroscopy analysis and (2) propagating ultrasonic guided waves-are used for this purpose. Both techniques revealed a reduction of the nonlinear behavior in the GRC material with ageing. Specimens are then loaded to failure to obtain their strength and stiffness. Compared to the un-aged specimens, the aged specimens are found to exhibit more linear behavior, have more stiffness but less toughness. Finally, undisturbed fragments on the fracture surface from mechanical tests are inspected under the electron microscope, to understand the fundamental mechanisms that cause the change in the GRC behavior with ageing.
• Eiras, J. N., Kundu, T., Bonilla, M., & Payá, J. (2013). Nondestructive monitoring of ageing of alkali resistant glass fiber reinforced cement (GRC). Journal of Nondestructive Evaluation, 32(3), 300-314.
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  Abstract: Glass fiber reinforced cement (GRC) is a composite material made of portland cement mortar and alkali resistant (AR) fibers. AR fibers are added to portland cement to give the material additional flexural strength and toughness. However, ageing deteriorates the fibers and as a result the improvement in the mechanical properties resulted from the fiber addition disappears as the structure becomes old. The aim of this paper is monitoring GRC ageing by nondestructive evaluation (NDE) techniques. Two different NDE techniques - (1) nonlinear impact resonant acoustic spectroscopy analysis and (2) propagating ultrasonic guided waves - are used for this purpose. Both techniques revealed a reduction of the nonlinear behavior in the GRC material with ageing. Specimens are then loaded to failure to obtain their strength and stiffness. Compared to the un-aged specimens, the aged specimens are found to exhibit more linear behavior, have more stiffness but less toughness. Finally, undisturbed fragments on the fracture surface from mechanical tests are inspected under the electron microscope, to understand the fundamental mechanisms that cause the change in the GRC behavior with ageing. © 2013 Springer Science+Business Media New York.
• Hu, B. o., Kundu, T., Grill, W., Liu, B., & Toufigh, V. (2013). Embedded Piezoelectric Sensors for Health Monitoring of Concrete Structures.. ACI Materials Journal, 110(2).
• Hu, B., Kundu, T., Grill, W., Liu, B., & Toufigh, V. (2013). Embedded Piezoelectric Sensors for Health Monitoring of Concrete Structures. ACI MATERIALS JOURNAL, 110(2), 149-158.
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  This paper presents an experimental investigation for detecting defects in concrete structures using so-called "smart aggregates." The smart aggregates are small cylinders with piezoelectric patches inside that can be embedded in concrete structures and used as both actuators and sensors. Specimens with different types of defects such as notch, hole, and inclusion were used in this study. To evaluate the effectiveness of the smart aggregates for detecting real cracks in concrete structures, three-point bending tests were carried out on two reinforced concrete beams. The test results indicate that not only the passive defects (notch, hole, or inclusion) but also the real cracks in reinforced concrete structures can be detected by the smart aggregates. Sensitivities of different parameters (time-of-flight, energy content of the signals, wavelet packet decomposition-based damage index) for various defects were also investigated.
• Korde, N., & Kundu, T. (2013). Material hardness and ageing measurement using guided ultrasonic waves. ULTRASONICS, 53(2), 506-510.
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  Elastic properties of materials can be easily determined from the ultrasonic wave velocity measurement. However, material hardness cannot be obtained from the ultrasonic wave speed. Heat treatment and ageing affect the microstructure of many materials changing their hardness and strength. It has been already established that ultrasonic attenuation and dispersion are also affected by the material microstructure. It is investigated in this paper if the attenuation of ultrasonic guided waves can be correlated with the material ageing or duration of heat treatment and material hardness. To this aim six identical aluminum 2024 alloy plate specimens were subjected to different durations of heat treatment at 150 degrees C and were inspected nondestructively propagating Lamb waves through the specimens. Attenuation of the Lamb wave was found to be inversely related to the hardness. Rockwell hardness test was performed to corroborate the ultrasonic observations. In comparison to the Rockwell hardness test the ultrasonic inspection was found to be more sensitive to the heat treatment duration and material ageing. From these results it is concluded that guided wave inspection method is a reliable and probably more desirable alternative for characterizing the hardness and microstructure of heat treated materials. Earlier investigations correlated the bulk wave attenuation with the material ageing while this work is the first attempt to correlate the guided wave attenuation to the material hardness and ageing. (C) 2012 Elsevier B.V. All rights reserved.
• Korde, N., & Kundu, T. (2013). Material hardness and ageing measurement using guided ultrasonic waves. Ultrasonics, 53(2), 506-510.
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  PMID: 23047018;Abstract: Elastic properties of materials can be easily determined from the ultrasonic wave velocity measurement. However, material hardness cannot be obtained from the ultrasonic wave speed. Heat treatment and ageing affect the microstructure of many materials changing their hardness and strength. It has been already established that ultrasonic attenuation and dispersion are also affected by the material microstructure. It is investigated in this paper if the attenuation of ultrasonic guided waves can be correlated with the material ageing or duration of heat treatment and material hardness. To this aim six identical aluminum 2024 alloy plate specimens were subjected to different durations of heat treatment at 150 °C and were inspected nondestructively propagating Lamb waves through the specimens. Attenuation of the Lamb wave was found to be inversely related to the hardness. Rockwell hardness test was performed to corroborate the ultrasonic observations. In comparison to the Rockwell hardness test the ultrasonic inspection was found to be more sensitive to the heat treatment duration and material ageing. From these results it is concluded that guided wave inspection method is a reliable and probably more desirable alternative for characterizing the hardness and microstructure of heat treated materials. Earlier investigations correlated the bulk wave attenuation with the material ageing while this work is the first attempt to correlate the guided wave attenuation to the material hardness and ageing. © 2012 Elsevier B.V. All rights reserved.
• Kundu, T. (2013). Mechanical Aerospace and Nuclear Engineering Department. Review of Progress in Quantitative Nondestructive Evaluation, 6, 109.
• Kundu, T. (2013). Proceedings of SPIE - The International Society for Optical Engineering: Introduction. Proceedings of SPIE - The International Society for Optical Engineering, 8695, xvii.
• Kundu, T., Korde, N., & Kundu, T. -. (2013). Material hardness and ageing measurement using guided ultrasonic waves. Ultrasonics, 53(2).
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  Elastic properties of materials can be easily determined from the ultrasonic wave velocity measurement. However, material hardness cannot be obtained from the ultrasonic wave speed. Heat treatment and ageing affect the microstructure of many materials changing their hardness and strength. It has been already established that ultrasonic attenuation and dispersion are also affected by the material microstructure. It is investigated in this paper if the attenuation of ultrasonic guided waves can be correlated with the material ageing or duration of heat treatment and material hardness. To this aim six identical aluminum 2024 alloy plate specimens were subjected to different durations of heat treatment at 150°C and were inspected nondestructively propagating Lamb waves through the specimens. Attenuation of the Lamb wave was found to be inversely related to the hardness. Rockwell hardness test was performed to corroborate the ultrasonic observations. In comparison to the Rockwell hardness test the ultrasonic inspection was found to be more sensitive to the heat treatment duration and material ageing. From these results it is concluded that guided wave inspection method is a reliable and probably more desirable alternative for characterizing the hardness and microstructure of heat treated materials. Earlier investigations correlated the bulk wave attenuation with the material ageing while this work is the first attempt to correlate the guided wave attenuation to the material hardness and ageing.
• Liu, P., Sohn, H., & Kundu, T. (2013). Noncontact fatigue crack detection using nonlinear wave modulation spectroscopy. The Journal of the Acoustical Society of America, 134(5), 4105--4105.
• Miller, T. H., Kundu, T., Huang, J., & Grill, J. Y. (2013). A new guided wave-based technique for corrosion monitoring in reinforced concrete. STRUCTURAL HEALTH MONITORING-AN INTERNATIONAL JOURNAL, 12(1), 35-47.
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  Guided waves have been used in the past for monitoring corrosion and other damages in plates, rods, pipes, and reinforced concrete structures. Past investigations tried to relate the recorded signal strength to the extent of corrosion or other damage. The main disadvantage of this approach is that the signal strength is also affected by the bonding condition between the sensors and the structure. Over time, this bonding condition is bound to deteriorate, and therefore, one cannot say for sure if the change in the signal strength is due to corrosion or because of the deterioration of the attachment of the sensors to the structure. A new guided wave-based technique is proposed here, which investigates the change in the time of flight of the propagating wave in loaded reinforced concrete structures at various levels of corrosion. Corrosion affects the bonding strength between concrete and reinforcing steel altering the stress level in the reinforcing steel bar in a loaded beam. Since the wave speed is affected by the internal stress, an increase in corrosion level should affect the wave speed in a steel bar and the wave's time of flight through the bar. The main advantage of the proposed approach is that this result should not be affected by the bonding condition between the sensor and the structure. How delamination at the bar-concrete interface affects the signal strength and the effect of induced corrosion in free bars as well as in bars embedded in the concrete are also investigated.
• Miller, T. H., Kundu, T., Huang, J., & Grill, J. Y. (2013). A new guided wave-based technique for corrosion monitoring in reinforced concrete. Structural Health Monitoring, 12(1), 35-47.
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  Abstract: Guided waves have been used in the past for monitoring corrosion and other damages in plates, rods, pipes, and reinforced concrete structures. Past investigations tried to relate the recorded signal strength to the extent of corrosion or other damage. The main disadvantage of this approach is that the signal strength is also affected by the bonding condition between the sensors and the structure. Over time, this bonding condition is bound to deteriorate, and therefore, one cannot say for sure if the change in the signal strength is due to corrosion or because of the deterioration of the attachment of the sensors to the structure. A new guided wave-based technique is proposed here, which investigates the change in the time of flight of the propagating wave in loaded reinforced concrete structures at various levels of corrosion. Corrosion affects the bonding strength between concrete and reinforcing steel altering the stress level in the reinforcing steel bar in a loaded beam. Since the wave speed is affected by the internal stress, an increase in corrosion level should affect the wave speed in a steel bar and the wave's time of flight through the bar. The main advantage of the proposed approach is that this result should not be affected by the bonding condition between the sensor and the structure. How delamination at the bar-concrete interface affects the signal strength and the effect of induced corrosion in free bars as well as in bars embedded in the concrete are also investigated. © The Author(s) 2012.
• Nakatani, H., Hajzargarbashi, T., Ito, K., Kundu, T., & Takeda, N. (2013). Locating point of impact on an anisotropic cylindrical surface using acoustic beamforming technique. Key Engineering Materials, 558, 331-340.
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  Abstract: A beamforming array technique with four sensors is applied to a cylindrical geometry for detecting point of impact. A linear array of acoustic sensors attached to the plate record the waveforms of Lamb waves generated at the impact point with individual time delay. A beamforming technique in conjunction with an optimization scheme that incorporates the direction dependent guided Lamb wave speed in cylindrical plates is developed. The optimization is carried out using the experimentally obtained wave speed as a function of propagation direction. The maximum value in the beamforming plot corresponds to the predicted point of impact. The proposed technique is experimentally verified by comparing the predicted points with the exact points of impact on a cylindrical aluminum plate and a cylindrical composite shell. For randomly chosen points of impact the beamforming technique successfully predicts the location of the acoustic source. © (2013) Trans Tech Publications, Switzerland.
• Yadav, S. K., Banerjee, S., & Kundu, T. (2013). On sequencing the feature extraction techniques for online damage characterization. JOURNAL OF INTELLIGENT MATERIAL SYSTEMS AND STRUCTURES, 24(4), 473-483.
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  The current state of the health-monitoring technology lacks a generalized and definitive approach to the identification and localization of mechanical damage in structural materials. In past decades, several signal-processing tools have been used for solving different health-monitoring problems but the commutability of the tools between different problems has been restricted. The fundamental reasons for this shortcoming have never been investigated in detail. A thorough study is presented in this article employing almost all promising feature extraction tools on a representative problem-a plate with rivet holes. The cracks around rivet holes in a joint panel of a steel truss bridge are very difficult to detect. Although well established, Lamb wave-based nondestructive evaluation techniques are revisited and new tools are developed to address this issue. The simulation of scattered ultrasonic wave field is carried out using the finite element method. This ultrasonic wave field is further analyzed to evaluate the integrity of the structure using various feature extraction techniques. The joint time-frequency-energy representation is obtained from ultrasonic signals recorded at various locations on the plate (joint panel) and used to extract damage-sensitive features. Those features were then used to formulate a new damage parameter for better visualization of the crack. The results are shown to demonstrate the comparative effectiveness of these techniques. It is concluded that any particular feature extraction technique cannot detect all possible sizes and orientations of the crack. It is suggested that the statistical occurrence and pattern of the crack must be visualized through few selective feature extraction techniques in a sequence.
• Yadav, S. K., Banerjee, S., & Kundu, T. (2013). On sequencing the feature extraction techniques for online damage characterization. Journal of Intelligent Material Systems and Structures, 24(4), 473-483.
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  Abstract: The current state of the health-monitoring technology lacks a generalized and definitive approach to the identification and localization of mechanical damage in structural materials. In past decades, several signal-processing tools have been used for solving different health-monitoring problems but the commutability of the tools between different problems has been restricted. The fundamental reasons for this shortcoming have never been investigated in detail. A thorough study is presented in this article employing almost all promising feature extraction tools on a representative problem - a plate with rivet holes. The cracks around rivet holes in a joint panel of a steel truss bridge are very difficult to detect. Although well established, Lamb wave-based nondestructive evaluation techniques are revisited and new tools are developed to address this issue. The simulation of scattered ultrasonic wave field is carried out using the finite element method. This ultrasonic wave field is further analyzed to evaluate the integrity of the structure using various feature extraction techniques. The joint time-frequency-energy representation is obtained from ultrasonic signals recorded at various locations on the plate (joint panel) and used to extract damage-sensitive features. Those features were then used to formulate a new damage parameter for better visualization of the crack. The results are shown to demonstrate the comparative effectiveness of these techniques. It is concluded that any particular feature extraction technique cannot detect all possible sizes and orientations of the crack. It is suggested that the statistical occurrence and pattern of the crack must be visualized through few selective feature extraction techniques in a sequence. © The Author(s) 2012.
• Ahmad, R., & Kundu, T. (2012). Influence of water flow through pipe networks for damage detection using guided waves. RILEM Bookseries, 6, 681-687.
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  Abstract: Researchers have been trying to develop techniques for early forecasting of the degradation process in pipe networks. Different Non Destructive Testing Techniques are used for detecting damages in a variety of materials and structures. Guided wave technique is a suitable non-destructive technique which can be used for pipe inspection by generating cylindrical guided waves. In this research, steel pipes are inspected using cylindrical guided waves. The purpose of this paper is to investigate the influence of flowing water through the pipe on the guided wave propagation in the pipe wall. Investigations are also carried out when the pipes are in open air which gives the traction-free boundary condition. It is also investigated whether the direction of the flow influences the propagation of the guided waves. Experimental V(f) curves are extracted from the received signals for defect free and defective pipe specimens and compared to study the effect of water flow on the strength and other characteristics of various guided wave modes. © RILEM 2013.
• Ahmad, R., & Kundu, T. (2012). Structural health monitoring of steel pipes under different boundary conditions and choice of signal processing techniques. Advances in Civil Engineering, 2012.
• Habib, A., Shelke, A., Pluta, M., Kundu, T., Pietsch, U., & Grill, W. (2012). Imaging of Acoustic Waves in Piezoelectric Ceramics by Coulomb Coupling. JAPANESE JOURNAL OF APPLIED PHYSICS, 51(7).
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  The transport properties of bulk and guided acoustic waves travelling in a lead zirconate titanate (PZT) disc, originally manufactured to serve as ultrasonic transducer, have been monitored by scanned Coulomb coupling. The images are recorded by excitation and detection of ultrasound with local electric field probes via piezoelectric coupling. A narrow pulse has been used for excitation. Broadband coupling is achieved since neither mechanical nor electrical resonances are involved. The velocities of the traveling acoustic waves determined from the images are compared with characteristic velocities calculated from material properties listed by the manufacturer of the PZT plate. (C) 2012 The Japan Society of Applied Physics
• Habib, A., Shelke, A., Pluta, M., Kundu, T., Pietsch, U., & Grill, W. (2012). Imaging of acoustic waves in piezoelectric ceramics by Coulomb coupling. Japanese Journal of Applied Physics, 51(7 PART2).
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  Abstract: The transport properties of bulk and guided acoustic waves travelling in a lead zirconate titanate (PZT) disc, originally manufactured to serve as ultrasonic transducer, have been monitored by scanned Coulomb coupling. The images are recorded by excitation and detection of ultrasound with local electric field probes via piezoelectric coupling. A narrow pulse has been used for excitation. Broadband coupling is achieved since neither mechanical nor electrical resonances are involved. The velocities of the traveling acoustic waves determined from the images are compared with characteristic velocities calculated from material properties listed by the manufacturer of the PZT plate. © 2012 The Japan Society of Applied Physics.
• Habib, A., Shelke, A., Pluta, M., Kundu, T., Pietsch, U., & Grill, W. (2012). Imaging of acoustic waves in piezoelectric ceramics by Coulomb coupling. Japanese Journal of Applied Physics, 51(7S), 07GB05.
• Habib, A., Shelke, A., Pluta, M., Pietsch, U., Kundu, T., & Grill, W. (2012). Scattering and attenuation of surface acoustic waves and surface skimming longitudinal polarized bulk waves imaged by Coulomb coupling. AIP Conference Proceedings, 1433, 247-250.
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  Abstract: Coulomb coupling has been applied for vector contrast imaging of surface acoustic waves and surface skimming longitudinal polarized waves travelling on or in a 5 mm thick, Y-Z cut Lithium Niobate single crystal. The excitation and detection of acoustic waves was performed by Coulomb coupling. For excitation 20 oscillations at a frequency of 89.9 MHz were used. The scattering and attenuation of both, surface skimming and surface acoustic waves are studied by imaging in vector contrast. Objects employed for interaction with the waves are layers of absorptive and scattering materials. The interaction allows a clear differentiation of volume waves skimming the surface and guided waves traveling at the surface. © 2012 American Institute of Physics.
• Habib, A., Shelke, A., Vogel, M., Pietsch, U., Jiang, X., & Kundu, T. (2012). Mechanical characterization of sintered piezo-electric ceramic material using scanning acoustic microscope. ULTRASONICS, 52(8), 989-995.
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  Lead Zirconate Titanate (PZT) is a piezo-electric ceramic material that needs to be characterized for its potential use in microelectronics. Energy dispersive X-ray analysis (EDX) is conducted to determine the chemical composition of the PZT ceramics. The scanning electron microscope (SEM) is performed to study the surface morphology, grain structure and grain boundaries. The SEM image helps us to understand the surface wave propagation and scattering phenomena by the PZT and the reason for its anisotropy and inhomogeneity due to the grain structure. In this paper scanning acoustic microscopy at 100 MHz excitation frequency is conducted for determining mechanical properties of Pit. Earlier works reported only the longitudinal wave speed in PZT while in this paper longitudinal, shear and surface acoustic wave speeds of sintered PZT are measured from its acoustic material signature (AMS) curves, also known as V(z) curves. AMS or V(z) curve is the variation of the output voltage as a function of the distance between the acoustic lens focal point and the reflecting surface. The average velocities of longitudinal, shear and surface acoustic waves in a PZT specimen are determined from its V(z) curve generated at 100 MHz excitation frequency and found to be over 5000 m/s, over 3000 m/s and between 2500 and 3000 m/s, respectively. From these velocities all elastic constants of the specimen are obtained. (C) 2012 Elsevier B.V. All rights reserved.
• Habib, A., Shelke, A., Vogel, M., Pietsch, U., Jiang, X., & Kundu, T. (2012). Mechanical characterization of sintered piezo-electric ceramic material using scanning acoustic microscope. Ultrasonics, 52(8), 989-995.
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  PMID: 22989949;Abstract: Lead Zirconate Titanate (PZT) is a piezo-electric ceramic material that needs to be characterized for its potential use in microelectronics. Energy dispersive X-ray analysis (EDX) is conducted to determine the chemical composition of the PZT ceramics. The scanning electron microscope (SEM) is performed to study the surface morphology, grain structure and grain boundaries. The SEM image helps us to understand the surface wave propagation and scattering phenomena by the PZT and the reason for its anisotropy and inhomogeneity due to the grain structure. In this paper scanning acoustic microscopy at 100 MHz excitation frequency is conducted for determining mechanical properties of PZT. Earlier works reported only the longitudinal wave speed in PZT while in this paper longitudinal, shear and surface acoustic wave speeds of sintered PZT are measured from its acoustic material signature (AMS) curves, also known as V(z) curves. AMS or V(z) curve is the variation of the output voltage as a function of the distance between the acoustic lens focal point and the reflecting surface. The average velocities of longitudinal, shear and surface acoustic waves in a PZT specimen are determined from its V(z) curve generated at 100 MHz excitation frequency and found to be over 5000 m/s, over 3000 m/s and between 2500 and 3000 m/s, respectively. From these velocities all elastic constants of the specimen are obtained. © 2012 Elsevier B.V. All rights reserved.
• Kabiri, R. E., Hajzargarbashi, T., & Kundu, T. (2012). Scattering of focused ultrasonic beams by cavities in a solid half-space. The Journal of the Acoustical Society of America, 132(2), 718--727.
• Koabaz, M., Hajzargarbashi, T., Kundu, T., & Deschamps, M. (2012). Locating the acoustic source in an anisotropic plate. STRUCTURAL HEALTH MONITORING-AN INTERNATIONAL JOURNAL, 11(3), 315-323.
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  By analyzing the arrival times of guided waves, the acoustic source in a plate is predicted. Solving this problem is important for continuous health monitoring of structures. Several techniques based on the triangulation principle have been proposed for this purpose but they do not work for anisotropic plates. The popular triangulation technique assumes that the wave velocity is the same in all directions, which is not true for anisotropic plates. An alternative method based on the optimization scheme was proposed by Kundu et al. (Kundu T, Das S and Jata KV. Point of impact prediction in isotropic and anisotropic plates from the acoustic emission data. J Acoust Soc Am 2007; 122(4): 2057-2066; Kundu T, Das S, Martin SA and Jata KV. Locating point of impact in anisotropic fiber reinforced composite plates. Ultrasonics 2008; 48(3): 193-201; Kundu T, Das S and Jata KV. Health monitoring of a thermal protection system using lamb waves. Struct Health Monit: Int J 2009; 8(1): 29-45; Kundu T, Das S and Jata KV. Detection of point of impact on a stiffened plate by the acoustic emission technique. Smart Mater Struct 2009; 18(3): 1-9) to locate the point of impact in anisotropic plates by analyzing the times of arrival of the ultrasonic signals received by the passive sensors attached to the plate. Recently, Hajzargarbashi et al. (Hajzargarbashi T, Kundu T and Bland S. An improved algorithm for detecting point of impact in anisotropic inhomogeneous plates. Ultrasonics 2010; 51(3): 317-324.) improved that technique. Following their modification, in this article, the acoustic source point in an anisotropic plate is predicted from the acoustic emission data with some additional modifications. Experiments are carried out with a carbon-epoxy plate. A parallel pre-stressed actuator is used as the acoustic source and the acoustic signals at different locations are received by adhesively bonded acoustic sensors. The source point is then predicted and compared with its actual location. Related theory and computed results of wave propagation in anisotropic plate are also presented and the theoretical predictions experimentally verified at frequencies higher than what is typically generated by the simple impact phenomenon.
• Koabaz, M., Hajzargarbashi, T., Kundu, T., & Deschamps, M. (2012). Locating the acoustic source in an anisotropic plate. Structural Health Monitoring, 11(3), 315-323.
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  Abstract: By analyzing the arrival times of guided waves, the acoustic source in a plate is predicted. Solving this problem is important for continuous health monitoring of structures. Several techniques based on the triangulation principle have been proposed for this purpose but they do not work for anisotropic plates. The popular triangulation technique assumes that the wave velocity is the same in all directions, which is not true for anisotropic plates. An alternative method based on the optimization scheme was proposed by Kunduet al.(Kundu T, Das S and Jata KV. Point of impact prediction in isotropic and anisotropic plates from the acoustic emission data. J Acoust Soc Am 2007; 122(4): 2057-2066; Kundu T, Das S, Martin SA and Jata KV. Locating point of impact in anisotropic fiber reinforced composite plates. Ultrasonics 2008; 48(3): 193-201; Kundu T, Das S and Jata KV. Health monitoring of a thermal protection system using lamb waves. Struct Health Monit: Int J 2009; 8(1): 29-45; Kundu T, Das S and Jata KV. Detection of point of impact on a stiffened plate by the acoustic emission technique. Smart Mater Struct 2009; 18(3): 1-9) to locate the point of impact in anisotropic plates by analyzing the times of arrival of the ultrasonic signals received by the passive sensors attached to the plate. Recently, Hajzargarbashiet al.(Hajzargarbashi T, Kundu T and Bland S. An improved algorithm for detecting point of impact in anisotropic inhomogeneous plates. Ultrasonics 2010; 51(3): 317-324.) improved that technique. Following their modification, in this article, the acoustic source point in an anisotropic plate is predicted from the acoustic emission data with some additional modifications. Experiments are carried out with a carbon-epoxy plate. A parallel pre-stressed actuator is used as the acoustic source and the acoustic signals at different locations are received by adhesively bonded acoustic sensors. The source point is then predicted and compared with its actual location. Related theory and computed results of wave propagation in anisotropic plate are also presented and the theoretical predictions experimentally verified at frequencies higher than what is typically generated by the simple impact phenomenon. © The Author(s) 2011.
• Kundu, T. (2012). 1 Mechanics of Elastic. Ultrasonic and Electromagnetic NDE for Structure and Material Characterization: Engineering and Biomedical Applications, 1.
• Kundu, T. (2012). Dianne M. Benson, Prasanna Karpur, Theodore E. Matikas Research Institute, University of Dayton 300 College Park Avenue Dayton OH 45469-0127. Review of Progress in Quantitative Nondestructive Evaluation: Volume 14A/14B, 14, 187.
• Kundu, T. (2012). Guided waves for nondestructive testing - experiment and analysis. RILEM Bookseries, 6, 567-576.
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  Abstract: Use of ultrasonic waves is continuously increasing for nondestructive evaluation (NDE) and structural health monitoring (SHM) in civil, aerospace, electrical, mechanical and bioengineering applications. Between bulk waves and guided waves, the latter is becoming more popular for NDE/SHM applications because the guided waves can propagate long distances and reach difficult to access regions. Recent advances in the research related to nondestructive testing (NDT) of composites and metals are discussed in this paper. To analyze the experimental results one often needs to understand the mechanics of wave propagation in various structures. Unfortunately, only for simple structures, such as homogeneous and layered half-spaces, plates, rods and pipes, the analytical solutions are available. Complex structural geometries with internal defects are difficult to solve analytically or numerically by the popular finite element method because at high frequencies the size of the finite elements becomes prohibitively small. An alternative mesh-free technique called the distributed point source method (DPSM) is being developed for solving such problems and is discussed here in addition to the experimental results. © RILEM 2013.
• Kundu, T., Nakatani, H., & Takeda, N. (2012). Acoustic source localization in anisotropic plates. ULTRASONICS, 52(6), 740-746.
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  The conventional triangulation technique cannot locate the acoustic source in an anisotropic plate because this technique requires the wave speed to be independent of the propagation direction which is not the case for an anisotropic plate. All methods proposed so far for source localization in anisotropic plates require either the knowledge of the direction dependent velocity profile or a dense array of sensors. In this paper for the first time a technique is proposed to locate the acoustic source in large anisotropic plates with the help of only six sensors without knowing the direction dependent velocity profile in the plate. Experimental results show that the proposed technique works for both isotropic and anisotropic structures. For isotropic plates the required number of sensors can be reduced from 6 to 4. (c) 2012 Elsevier B.V. All rights reserved.
• Kundu, T., Nakatani, H., & Takeda, N. (2012). Acoustic source localization in anisotropic plates. Ultrasonics, 52(6), 740-746.
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  PMID: 22381813;Abstract: The conventional triangulation technique cannot locate the acoustic source in an anisotropic plate because this technique requires the wave speed to be independent of the propagation direction which is not the case for an anisotropic plate. All methods proposed so far for source localization in anisotropic plates require either the knowledge of the direction dependent velocity profile or a dense array of sensors. In this paper for the first time a technique is proposed to locate the acoustic source in large anisotropic plates with the help of only six sensors without knowing the direction dependent velocity profile in the plate. Experimental results show that the proposed technique works for both isotropic and anisotropic structures. For isotropic plates the required number of sensors can be reduced from 6 to 4. © 2012 Elsevier B.V. All rights reserved.
• Kundu, T., Rahni, E. K., Hajzargarbashi, T., & Kundu, T. -. (2012). Scattering of focused ultrasonic beams by cavities in a solid half-space. The Journal of the Acoustical Society of America, 132(2).
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  The ultrasonic field generated by a point focused acoustic lens placed in a fluid medium adjacent to a solid half-space, containing one or more spherical cavities, is modeled. The semi-analytical distributed point source method (DPSM) is followed for the modeling. This technique properly takes into account the interaction effect between the cavities placed in the focused ultrasonic field, fluid-solid interface and the lens surface. The approximate analytical solution that is available in the literature for the single cavity geometry is very restrictive and cannot handle multiple cavity problems. Finite element solutions for such problems are also prohibitively time consuming at high frequencies. Solution of this problem is necessary to predict when two cavities placed in close proximity inside a solid can be distinguished by an acoustic lens placed outside the solid medium and when such distinction is not possible.
• Nakatani, H., Hajzargarbashi, T., Ito, K., Kundu, T., & Takeda, N. (2012). Impact localization on a cylindrical plate by near-field beamforming analysis. Proceedings of SPIE - The International Society for Optical Engineering, 8345.
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  Abstract: A beamforming array technique with 4 sensors is applied to a cylindrical plate for detecting point of impact. Linear array of acoustic sensors attached to the plate record the waveforms of Lamb waves generated at the impact point with individual time delay. An optimization technique with an objective function is incorporated into the beamforming technique in order to deal with the direction dependent Lamb wave speeds in a cylindrical geometry. The optimization is carried out using the experimentally obtained wave speed as a function of propagation direction. The maximum point in beamforming plot with minimized objective function corresponds to the localized point of impact. The proposed technique is experimentally verified by comparing the predicted points with the exact points of impact on a cylindrical aluminum plate. For randomly chosen points of impact the beamforming technique successfully predicts location of the exact acoustic source. © 2012 SPIE.
• Placko, D., Bore, T., & Kundu, T. (2012). 4 Distributed Point Source Method for Modeling and Imaging in Electrostatic and Electromagnetic Problems. Ultrasonic and Electromagnetic NDE for Structure and Material Characterization: Engineering and Biomedical Applications, 249.
• Rahani, E. K., & Kundu, T. (2012). Electromagnetic THz Radiation Modeling by DPSM. JOURNAL OF INFRARED MILLIMETER AND TERAHERTZ WAVES, 33(3), 376-390.
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  THz or T-ray imaging and spectroscopy are becoming increasingly popular nondestructive evaluation techniques for damage detection and characterization of materials. In order to understand the interaction between the T-ray electromagnetic waves and dielectric media a reliable model of electromagnetic wave propagation through dielectric materials must be developed. A recently developed semi-analytical method called the distributed point source method (DPSM) is extended to model electromagnetic wave propagation in THz range. Since T-ray signals generated by emitters or sources are close to Gaussian beams, the DPSM modeling is carried out for Gaussian beams generated by finite sized emitters. The DPSM generated results are compared with the analytical and experimental results. T-ray propagation in layered structures in absence of any anomaly and the interaction between the Gaussian beam and the spherical scatterer are also investigated.
• Rahani, E. K., & Kundu, T. (2012). Electromagnetic THz radiation modeling by DPSM. Journal of Infrared, Millimeter, and Terahertz Waves, 33(3), 376-390.
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  Abstract: THz or T-ray imaging and spectroscopy are becoming increasingly popular nondestructive evaluation techniques for damage detection and characterization of materials. In order to understand the interaction between the T-ray electromagnetic waves and dielectric media a reliable model of electromagnetic wave propagation through dielectric materials must be developed. A recently developed semi-analytical method called the distributed point source method (DPSM) is extended to model electromagnetic wave propagation in THz range. Since T-ray signals generated by emitters or sources are close to Gaussian beams, the DPSM modeling is carried out for Gaussian beams generated by finite sized emitters. The DPSM generated results are compared with the analytical and experimental results. T-ray propagation in layered structures in absence of any anomaly and the interaction between the Gaussian beam and the spherical scatterer are also investigated. © Springer Science+Business Media, LLC 2012.
• Rahni, E. K., Hajzargarbashi, T., & Kundu, T. (2012). Scattering of focused ultrasonic beams by cavities in a solid half-space. Journal of the Acoustical Society of America, 132(2), 718-727.
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  PMID: 22894194;Abstract: The ultrasonic field generated by a point focused acoustic lens placed in a fluid medium adjacent to a solid half-space, containing one or more spherical cavities, is modeled. The semi-analytical distributed point source method (DPSM) is followed for the modeling. This technique properly takes into account the interaction effect between the cavities placed in the focused ultrasonic field, fluid-solid interface and the lens surface. The approximate analytical solution that is available in the literature for the single cavity geometry is very restrictive and cannot handle multiple cavity problems. Finite element solutions for such problems are also prohibitively time consuming at high frequencies. Solution of this problem is necessary to predict when two cavities placed in close proximity inside a solid can be distinguished by an acoustic lens placed outside the solid medium and when such distinction is not possible. © 2012 Acoustical Society of America.
• Rahni, E. K., Rahni, E. K., Hajzargarbashi, T., Hajzargarbashi, T., Kundu, T., & Kundu, T. (2012). Scattering of focused ultrasonic beams by cavities in a solid half-space. JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA, 132(2), 718-727.
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  The ultrasonic field generated by a point focused acoustic lens placed in a fluid medium adjacent to a solid half-space, containing one or more spherical cavities, is modeled. The semi-analytical distributed point source method (DPSM) is followed for the modeling. This technique properly takes into account the interaction effect between the cavities placed in the focused ultrasonic field, fluid-solid interface and the lens surface. The approximate analytical solution that is available in the literature for the single cavity geometry is very restrictive and cannot handle multiple cavity problems. Finite element solutions for such problems are also prohibitively time consuming at high frequencies. Solution of this problem is necessary to predict when two cavities placed in close proximity inside a solid can be distinguished by an acoustic lens placed outside the solid medium and when such distinction is not possible. (C) 2012 Acoustical Society of America. [http://dx.doi.org/10.1121/1.4730895]
• Shelke, A., Amjad, U., Vasiljevic, M., Kundu, T., & Grill, W. (2012). Extracting quantitative information on pipe wall damage in absence of clear signals from defect. Journal of Pressure Vessel Technology, Transactions of the ASME, 134(5).
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  Abstract: It has been well established that guided waves are sensitive to structural damages encountered on their path of propagation and for this reason this technique is very efficient for distinguishing defective structural components from defect-free ones. Although the guided wave technique can identify a specimen having a distribution of defects, detecting and quantifying a small defect on its path from a long distance, as required for structural health monitoring (SHM) applications, is not an easy task for the guided wave inspection technique even today, especially when the transducers cannot come in direct contact with the pipe wall. The current technological challenges for pipe inspection by generating guided waves using noncontact transducers are to detect a small defect on the pipe wall and estimate its location and size from a long distance when the reflected signal from the defect cannot be clearly identified as is the case for low frequency guided waves that can propagate long distances. Electro-magnetic acoustic transducers (EMATs) are used here to generate guided waves in the pipe by the noncontact technique. This paper shows how small a defect in a pipe wall can be detected and its location and dimension can be estimated using relatively low frequency guided waves generated and received by EMATs even when the defect signal is not clearly visible in the time history plot because various wave modes reflected from the defect and pipe ends overlap. © 2012 American Society of Mechanical Engineers.
• Shelke, A., Amjad, U., Vasiljevic, M., Kundu, T., & Grill, W. (2012). Extracting quantitative information on pipe wall damage in absence of clear signals from defect. Journal of Pressure Vessel Technology, 134(5), 051502.
• Shelke, A., Brand, S., Kundu, T., Bereiter-Hahn, J., & Blasé, C. (2012). Mechanical property quantification of endothelial cells using scanning acoustic microscopy. Proceedings of SPIE - The International Society for Optical Engineering, 8348.
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  Abstract: The mechanical properties of cells reflect dynamic changes of cellular organization which occur during physiologic activities like cell movement, cell volume regulation or cell division. Thus the study of cell mechanical properties can yield important information for understanding these physiologic activities. Endothelial cells form the thin inner lining of blood vessels in the cardiovascular system and are thus exposed to shear stress as well as tensile stress caused by the pulsatile blood flow. Endothelial dysfunction might occur due to reduced resistance to mechanical stress and is an initial step in the development of cardiovascular disease like, e.g., atherosclerosis. Therefore we investigated the mechanical properties of primary human endothelial cells (HUVEC) of different age using scanning acoustic microscopy at 1.2 GHz. The HUVECs are classified as young (t D < 90 h) and old (t D > 90 h) cells depending upon the generation time for the population doubling of the culture (t D). Longitudinal sound velocity and geometrical properties of cells (thickness) were determined using the material signature curve V(z) method for variable culture condition along spatial coordinates. The plane wave technique with normal incidence is assumed to solve two-dimensional wave equation. The size of the cells is modeled using multilayered (solid-fluid) system. The propagation of transversal wave and surface acoustic wave are neglected in soft matter analysis. The biomechanical properties of HUVEC cells are quantified in an age dependent manner. © 2012 SPIE.
• Shelke, A., Shelke, A., Amjad, U., Amjad, U., Vasiljevic, M., Vasiljevic, M., Kundu, T., Kundu, T., Grill, W., & Grill, W. (2012). Extracting Quantitative Information on Pipe Wall Damage in Absence of Clear Signals From Defect. JOURNAL OF PRESSURE VESSEL TECHNOLOGY-TRANSACTIONS OF THE ASME, 134(5).
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  It has been well established that guided waves are sensitive to structural damages encountered on their path of propagation and for this reason this technique is very efficient for distinguishing defective structural components from defect-free ones. Although the guided wave technique can identify a specimen having a distribution of defects, detecting and quantifying a small defect on its path from a long distance, as required for structural health monitoring (SHM) applications, is not an easy task for the guided wave inspection technique even today, especially when the transducers cannot come in direct contact with the pipe wall. The current technological challenges for pipe inspection by generating guided waves using noncontact transducers are to detect a small defect on the pipe wall and estimate its location and size from a long distance when the reflected signal from the defect cannot be clearly identified as is the case for low frequency guided waves that can propagate long distances. Electro-magnetic acoustic transducers (EMATs) are used here to generate guided waves in the pipe by the noncontact technique. This paper shows how small a defect in a pipe wall can be detected and its location and dimension can be estimated using relatively low frequency guided waves generated and received by EMATs even when the defect signal is not clearly visible in the time history plot because various wave modes reflected from the defect and pipe ends overlap. [DOI: 10.1115/1.4005877]
• Wada, Y., Kundu, T., & Nakamura, K. (2012). Mesh-free distributed point source method for modeling guided wave propagation in a viscous fluid layer trapped between two solid plates. The Journal of the Acoustical Society of America, 132(3), 1963--1963.
• Yang, W., & Kundu, T. (2012). Department of Civil Engineering and Engineering Mechanics University of Arizona, Tucson, AZ 85721. Acoustical Imaging, 21, 23.
• Ahmad, R., & Kundu, T. (2011). Cylindrical guided wave signals for underground pipe inspection using different continuous wavelet mother functions. Journal of Civil Engineering and Architecture, 5(12), 1103.
• Blase, C., Shelke, A., Kundu, T., & Bereiter-Hahn, J. (2011). Elastic characterization of swine aorta by scanning acoustic microscopy at 30 MHz. Proceedings of SPIE - The International Society for Optical Engineering, 7984.
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  Abstract: The mechanical properties of blood vessel walls are important determinants of physiology and pathology of the cardiovascular system. Acoustic imaging (B mode) is routinely used in a clinical setting to determine blood flow and wall distensibility. In this study scanning acoustic microscopy in vitro is used to determine spatially resolved tissue elastic properties. Broadband excitation of 30 MHz has been applied through scanning acoustic microscopy (SAM) for topographical imaging of swine thoracic aorta in reflection mode. Three differently treated tissue samples were investigated with SAM: a) treated with elastase to remove elastin, b) autoclaving for 5 hours to remove collagen and c) fresh controlled untreated sample as control. Experimental investigations are conducted for studying the contribution of individual protein components (elastin and collagen) to the material characteristics of the aortic wall. Conventional tensile testing has been conducted on the tissue samples to study the mechanical behavior. The mechanical properties measured by SAM and tensile testing show qualitative agreement. © 2011 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).
• Dube, M., & Kundu, T. (2011). Closure to "Discussion of yield function for solder elastoviscoplastic modeling'" (2005, ASME J. Electron. Packag., 127, pp. 147-156). Journal of Electronic Packaging, Transactions of the ASME, 133(4).
• Dube, M., & Kundu, T. (2011). Closure to “Discussion of ‘Yield Function for Solder Elastoviscoplastic Modeling’”(2005, ASME J. Electron. Packag., 127, pp. 147--156). Journal of Electronic Packaging, 133(4), 045502.
• Graham, H. K., Akhtar, R., Kridiotis, C., Derby, B., Kundu, T., Trafford, A. W., & Sherratt, M. J. (2011). Localised micro-mechanical stiffening in the ageing aorta. Mechanisms of Ageing and Development, 132(10), 459-467.
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  PMID: 21777602;PMCID: PMC3192262;Abstract: Age-related loss of tissue elasticity is a common cause of human morbidity and arteriosclerosis (vascular stiffening) is associated with the development of both fatal strokes and heart failure. However, in the absence of appropriate micro-mechanical testing methodologies, multiple structural remodelling events have been proposed as the cause of arteriosclerosis. Therefore, using a model of ageing in female sheep aorta (young: 8 years) we: (i) quantified age-related macro-mechanical stiffness, (ii) localised in situ micro-metre scale changes in acoustic wave speed (a measure of tissue stiffness) and (iii) characterised collagen and elastic fibre remodelling. With age, there was an increase in both macro-mechanical stiffness and mean microscopic wave speed (and hence stiffness; young wave speed: 1701±1ms -1, old wave speed: 1710±1ms -1, p
• Hajzargarbashi, T., Nakatani, H., Kundu, T., & Takeda, N. (2011). Detecting the point of impact on a cylindrical plate by the acoustic emission technique. Proceedings of SPIE - The International Society for Optical Engineering, 7981.
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  Abstract: An optimization based technique for detecting the impact point on isotropic and anisotropic flat plates developed by Kundu and his associates is extended here to the cylindrical geometry. An objective function is defined that uses the cylindrical coordinates of four sensors attached to the cylinder and four arrival times to locate the point of impact by minimizing the objective function that gives the least squares error. The proposed technique is experimentally verified by predicting the points of impact and comparing the predicted points with the actual points of impact. © 2011 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).
• Hajzargarbashi, T., Nakatani, H., Kundu, T., & Takeda, N. (2011). Detecting the point of impact on an anisotropic cylindrical surface using only four acoustic sensors. Structural Health Monitoring 2011: Condition-Based Maintenance and Intelligent Structures - Proceedings of the 8th International Workshop on Structural Health Monitoring, 1, 562-569.
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  Abstract: An optimization based technique for detecting the point of impact on isotropic and anisotropic plates was developed by Kundu and his associates. Acoustic sensors attached to the plate record the arrival times of Lamb waves generated at the impact point. An objective function is then minimized to obtain the impact location [1-3]. Recently this technique has been extended to the cylindrical geometry. This optimization based technique has been tested on both flat plates and cylindrical shells made of aluminum [4]. In this paper the impact point on an anisotropic cylindrical shell geometry made of carbon fiber reinforced composite is investigated. One shortcoming of the previous method of requiring a large number of acoustic sensors to obtain the direction dependent velocity profile is also overcome here. In the new method the velocity profile in the anisotropic shell is obtained using only four sensors. Predicted points of impact on the anisotropic cylindrical shell are compared with the actual impact points. Good agreement between the two sets is observed.
• Hajzargarbashi, T., Nakatani, H., Kundu, T., Takeda, N., & others, . (2011). Detecting the point of impact on an anisotropic cylindrical surface using only four acoustic sensors. Ultrasonic Non-Destructive Evaluation: Impact Point Prediction and Simulation of Ultrasonic Fields, 61.
• Hajzargarbashi, T., Rahani, E. K., & Kundu, T. (2011). Scattering of focused ultrasonic beams by two spherical cavities in close proximity. IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, 58(8), 1619-1627.
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  PMID: 21859581;Abstract: Ultrasonic fields generated by one and two spherical cavities placed in front of a point-focused acoustic lens are modeled by the semi-analytical distributed point source method (DPSM). Results are generated by properly considering the interaction effect between two cavities placed in the focused ultrasonic field. The interaction effect between the two cavities prohibits the linear superposition of single cavity solutions to obtain the solution for two cavities placed in close proximity. Therefore, although some analytical and semi-analytical solutions are available for the single cavity in a focused ultrasonic field, those solutions cannot be simply superimposed for solving the two-cavity problem even for a linear elastic material. Solution of this problem is necessary to evaluate when two cavities placed in close proximity can be distinguished by an acoustic lens and when it is not possible. The comparison between the reflections of ultrasonic energy from two small cavities versus a single big cavity is also investigated. © 2011 IEEE.
• Hajzargarbashi, T., Rahani, E. K., & Kundu, T. (2011). Scattering of focused ultrasonic beams by two spherical cavities in close proximity. IEEE transactions on ultrasonics, ferroelectrics, and frequency control, 58(8).
• Hajzargerbashi, T., Kundu, T., & Bland, S. (2011). An improved algorithm for detecting point of impact in anisotropic inhomogeneous plates. ULTRASONICS, 51(3), 317-324.
• Hajzargerbashi, T., Kundu, T., & Bland, S. (2011). An improved algorithm for detecting point of impact in anisotropic inhomogeneous plates. Ultrasonics, 51(3), 317-324.
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  PMID: 21111437;Abstract: Conventional triangulation techniques fail to correctly predict the acoustic source location in anisotropic plates due to the direction dependent nature of the elastic wave speeds. To overcome this problem, Kundu et al. [1] proposed an alternative method for acoustic source prediction based on optimizing an objective function. They defined an objective function that uses the time of flight information of the acoustic waves to the passive transducers attached to the plate and the wave propagation direction (θ) from the source point to the receiving sensors. Some weaknesses of the original algorithm proposed in Ref. [1] were later overcome by developing a modified objective function [2]. A new objective function is introduced here to further simplify the optimization procedure and improve the computational efficiency. A new algorithm for source location is also introduced here to increase the source location accuracy. The performance of the objective function and source location algorithm were experimentally verified on a homogeneous anisotropic plate and a non-homogeneous anisotropic plate with a doubler patch. Results from these experiments indicate that the new objective function and source location algorithm have improved performance when compared with those discussed in Refs. [1,2]. © 2010 Elsevier B.V. All rights reserved.
• Koabaz, M., Hajzargarbashi, T., Kundu, T., & Deschamps, M. (2011). Prediction of the point of impact in an anisotropic plate. Journal of Physics: Conference Series, 269(1).
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  Abstract: Locating the point of impact of a foreign object in a plate is important for continuous health monitoring of structures. A new method based on an optimization scheme has been recently proposed to locate the point of impact in anisotropic plates by analyzing the times of arrival of the ultrasonic signals at the passive sensors attached to the plate. Following this optimization based technique, in this paper the impact point on an anisotropic plate is predicted from the acoustic emission data. Experiments are carried out with a carbon-epoxy plate where the impact point is modeled by an acoustic source. A Parallel Pre-stressed Actuator (PPA) is used as the acoustic source and the acoustic signals at different locations are received by adhesively bonded acoustic sensors. The source point is then predicted and compared with its actual location. Related theory is also presented in the paper. © Published under licence by IOP Publishing Ltd.
• Kundu, T. (2011). Proceedings of SPIE - The International Society for Optical Engineering: Introduction. Proceedings of SPIE - The International Society for Optical Engineering, 7984, xvii.
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  Abstract: This PDF file contains the front matter associated with SPIE Proceedings Volume 7984, including the Title Page, Copyright information, Table of Contents, Introduction, and the Conference Committee listing. © 2011 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).
• Kundu, T., Hajzargarbashi, T., Rahani, E., & Kundu, T. -. (2011). Scattering of focused ultrasonic beams by two spherical cavities in close proximity. IEEE transactions on ultrasonics, ferroelectrics, and frequency control, 58(8).
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  Ultrasonic fields generated by one and two spherical cavities placed in front of a point-focused acoustic lens are modeled by the semi-analytical distributed point source method (DPSM). Results are generated by properly considering the interaction effect between two cavities placed in the focused ultrasonic field. The interaction effect between the two cavities prohibits the linear superposition of single cavity solutions to obtain the solution for two cavities placed in close proximity. Therefore, although some analytical and semi-analytical solutions are available for the single cavity in a focused ultrasonic field, those solutions cannot be simply superimposed for solving the two-cavity problem even for a linear elastic material. Solution of this problem is necessary to evaluate when two cavities placed in close proximity can be distinguished by an acoustic lens and when it is not possible. The comparison between the reflections of ultrasonic energy from two small cavities versus a single big cavity is also investigated.
• Kundu, T., Kabiri, R. E., & Hajzargerbashi, T. (2011). Distributed point source method and its applications in solving acoustic wave scattering problems. The Journal of the Acoustical Society of America, 130(4), 2436--2436.
• Kundu, T., Rahani, E. K., & Kundu, T. -. (2011). Gaussian-DPSM (G-DPSM) and Element Source Method (ESM) modifications to DPSM for ultrasonic field modeling. Ultrasonics, 51(5).
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  In the last few years, Distributed Point Source Method (DPSM) a mesh-free semi-analytical technique has been developed. In spite of its many advantages, one shortcoming of the conventional DPSM method is that the field obtained by conventional DPSM method needs to be scaled to match the theoretical solutions. Two modification techniques called Gaussian-DPSM (G-DPSM) and Element Source Method (ESM) are developed here to avoid the scaling need. G-DPSM technique introduces additional fictitious point sources around every parent point source. Gaussian weight functions determine the strength of these additional fictitious point sources that are denoted as child point sources. ESM replaces discrete point sources used in the conventional DPSM by continuous sources. In the ESM formulation individual point sources are denoted as nodes. Special elements are formed on the boundary by connecting these nodes. The source strength inside the element can vary linearly or non-linearly depending on the order of the interpolation function used inside the element. Results generated by both these methods are compared with the conventional DPSM solution and analytical solution. It is shown that the ultrasonic field in front of the transducer computed by G-DPSM and ESM matches very well with the theory without using any scaling factor.
• Kundu, T., Rahani, E. K., & Kundu, T. -. (2011). Modeling of transient ultrasonic wave propagation using the distributed point. IEEE transactions on ultrasonics, ferroelectrics, and frequency control, 58(10).
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  Transient ultrasonic waves in a fluid medium generated by a flat circular and a point-focused transducer of finite size are modeled by the distributed point source method (DPSM). DPSM is a Green's-function-based semi-analytical mesh-free technique which is modified here to incorporate the transient loading from a finite-sized acoustic transducer. Conventional DPSM solves acoustic problems in steady-state frequency domain. Here, DPSM is extended to the time domain without the fast Fourier transform (FFT) but using the Green's function in the time domain. This modified method is denoted t-DPSM. Harmonic point sources of DPSM are replaced by time-dependent point sources in t-DPSM. Generated t-DPSM results are compared with the finite element (FE) results for both focused and flat circular transducers. The developed method is used to solve the transient problem of wave scattering by an air bubble in a fluid as the bubble is moved horizontally or vertically from the focal point of the focused transducer. The received energy signal is compared for different eccentricities.
• Rahani, E. K., & Kundu, T. (2011). Gaussian-DPSM (G-DPSM) and element source method (ESM) modifications to DPSM for ultrasonic field modeling. Ultrasonics, 51(5), 625-631.
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  PMID: 21300391;Abstract: In the last few years, Distributed Point Source Method (DPSM) a mesh-free semi-analytical technique has been developed. In spite of its many advantages, one shortcoming of the conventional DPSM method is that the field obtained by conventional DPSM method needs to be scaled to match the theoretical solutions. Two modification techniques called Gaussian-DPSM (G-DPSM) and Element Source Method (ESM) are developed here to avoid the scaling need. G-DPSM technique introduces additional fictitious point sources around every parent point source. Gaussian weight functions determine the strength of these additional fictitious point sources that are denoted as child point sources. ESM replaces discrete point sources used in the conventional DPSM by continuous sources. In the ESM formulation individual point sources are denoted as nodes. Special elements are formed on the boundary by connecting these nodes. The source strength inside the element can vary linearly or non-linearly depending on the order of the interpolation function used inside the element. Results generated by both these methods are compared with the conventional DPSM solution and analytical solution. It is shown that the ultrasonic field in front of the transducer computed by G-DPSM and ESM matches very well with the theory without using any scaling factor. © 2010 Elsevier B.V. All rights reserved.
• Rahani, E. K., & Kundu, T. (2011). Modeling of transient ultrasonic wave propagation using the distributed point Source Method. IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, 58(10), 2213-2221.
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  PMID: 21989885;Abstract: Transient ultrasonic waves in a fluid medium generated by a flat circular and a point-focused transducer of finite size are modeled by the distributed point source method (DPSM). DPSM is a Green's-function-based semi-analytical mesh-free technique which is modified here to incorporate the transient loading from a finite-sized acoustic transducer. Conventional DPSM solves acoustic problems in steady-state frequency domain. Here, DPSM is extended to the time domain without the fast Fourier transform (FFT) but using the Green's function in the time domain. This modified method is denoted t-DPSM. Harmonic point sources of DPSM are replaced by time-dependent point sources in t-DPSM. Generated t-DPSM results are compared with the finite element (FE) results for both focused and flat circular transducers. The developed method is used to solve the transient problem of wave scattering by an air bubble in a fluid as the bubble is moved horizontally or vertically from the focal point of the focused transducer. The received energy signal is compared for different eccentricities. © 2011 IEEE.
• Rahani, E. K., & Kundu, T. (2011). Modeling of transient ultrasonic wave propagation using the distributed point. IEEE transactions on ultrasonics, ferroelectrics, and frequency control, 58(10).
• Rahani, E. K., Hajzargarbashi, T., & Kundu, T. (2011). Distributed point source method and its applications in solving acoustic wave scattering problems. Proceedings of Meetings on Acoustics, 14.
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  Abstract: A recently developed semi-analytical technique called distributed point source method (DPSM) is used for solving various wave scattering problems. Scattering of focused ultrasonic fields by air bubbles or cavities in solid media is investigated here. Results for both single and multiple cavity geometries are presented. It is investigated when two cavities in close proximity can be distinguished and when it is not possible. The interaction effect between two cavities prohibits simple linear superposition of single cavity solutions to obtain the solution for the two cavities placed in close proximity. Therefore, although some analytical and semi-analytical solutions are available for the single cavity in a focused ultrasonic field, those solutions cannot be simply superimposed for solving the two-cavity problem even in a linear elastic material. The comparison between the ultrasonic energies reflected from two small cavities versus a single big cavity is also investigated. © 2011 Acoustical Society of America.
• Rahani, E. K., Kundu, T., Wu, Z., & Xin, H. (2011). Heat induced damage detection by terahertz (THz) radiation. Journal of Infrared, Millimeter, and Terahertz Waves, 32(6), 848--856.
• Rahani, E. K., Kundu, T., Wu, Z., & Xin, H. (2011). Mechanical damage detection in polymer tiles by THz radiation. IEEE Sensors Journal, 11(8), 1720--1725.
• Rivollet, A., Placko, D., & Kundu, T. (2011). Introducing a user-friendly MATLAB-based application interface software (AIS) for DPSM modeling - Applied to ultrasonic problems. Proceedings of SPIE - The International Society for Optical Engineering, 7984.
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  Abstract: This paper discusses the reasons why we need to change our habit of developing quick software to validate our theoretical results. It is explained here how to create computer programs, to use high level functions and to have a team's common strategy. To achieve this goal, an innovative concept of software development is presented, called AIS (Application Interface Software). This concept is illustrated by developing DPSM (Distributed Point Source Method) programs which is used for 3D ultrasonic field modeling. © 2011 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).
• Shelke, A., Banerjee, S., Kundu, T., Amjad, U., & Grill, W. (2011). Erratum: Multi-scale damage state estimation in composites using nonlocal elastic kernel: An experimental validation (International Journal of Solids and Structures (2011) 48 (1219-1228)). International Journal of Solids and Structures, 48(14-15), 2264-.
• Shelke, A., Banerjee, S., Kundu, T., Amjad, U., & Grill, W. (2011). Multi-scale damage state estimation in composites using nonlocal elastic kernel: An experimental validation. International Journal of Solids and Structures, 48(7-8), 1219-1228.
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  Abstract: In recent years early detection of structural damage (detecting incubation of damage) has received great attention in the structural health monitoring field. However, extraction of lower scale information to quantify the degree of damage is a challenging task, especially when the detection is based on macro-scale acoustic wave signals. All materials exhibit dependence on the intrinsic length scale. An attempt is made in this paper to extract lower scale feature from the macro-scale wave signal using nonlocal elasticity theory. The Christoffel solution has been modified using nonlocal parameters. The dispersion curves are generated for anisotropic solids using perturbation parameter through nonlocal theory. Dispersion curves are sensitive to initiation of damage in anisotropic solids at the intrinsic-length scale. In this paper detection of initiation of damage in a 4 mm carbon composite plate is demonstrated by employing nonlocal perturbation parameter and formulating a new Nonlocal Damage Index (NDI). The nonlocal theory is used to demonstrate the early prediction of failure of the system and to show progressive evolution of the damage. © 2011 Elsevier Ltd. All rights reserved.
• Shelke, A., Habib, A., Amjad, U., Pluta, M., Kundu, T., Pietsch, U., & Grill, W. (2011). Metamorphosis of bulk waves to Lamb waves in anisotropic piezoelectric crystals. Proceedings of SPIE - The International Society for Optical Engineering, 7984.
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  Abstract: Acoustic bulk waves were excited by local electric field probe in an anisotropic piezo-electric crystal Lithium Niobate (X-cut). A narrow pulse with a width of 25 ns was used for excitation to obtain wide frequency content in the Fourier domain. A wide spectrum ensures metamorphosis of bulk waves into Lamb waves for scan lengths comparable to the involved wavelengths. The low frequency content experiences multiple reflections from the two surfaces of the plate and disperses along the propagation direction. Acoustic bulk wave's evolution and transformation to Lamb waves are illustrated and explained with the aid of the Lamb wave dispersion phenomenon. The holographic images in the Fourier domain exemplify the metamorphosis of waves during propagation following the excitation at an approximate point source. © 2011 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).
• Shelke, A., Kundu, T., Amjad, U., Hahn, K., & Grill, W. (2011). Mode-selective excitation and detection of ultrasonic guided waves for delamination detection in laminated aluminum plates. IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, 58(3), 567-577.
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  PMID: 21429847;Abstract: Selective modes of guided Lamb waves are generated in a laminated aluminum plate for damage detection using a broadband piezoelectric transducer structured with a rigid electrode. Appropriate excitation frequencies and modes for inspection are selected from theoretical and experimental dispersion curves. Dispersion curves are obtained experimentally by short time Fourier transform of the transient signals. Sensitivity of antisymmetric and symmetric modes for delamination detection are investigated. The antisymmetric mode is found to be more reliable for delamination detection. Unlike other studies, in which the attenuation of the propagating waves is related to the extent of the internal damage, in this investigation, the changes in the time-of-flight (TOF) of guided Lamb waves are related to the damage progression. The mode conversion phenomenon of Lamb waves during progressive delamination is investigated. Close matching between the theoretical and experimentally derived dispersion curves and TOF assures the reliability of the results presented here. © 2011 IEEE.
• Shelke, A., Kundu, T., Amjad, U., Hahn, K., & Grill, W. (2011). Mode-selective excitation and detection of ultrasonic guided waves for delamination detection in laminated aluminum plates. IEEE Transactions on ultrasonics, ferroelectrics, and frequency control, 58(3).
• Yadav, S. K., Banerjee, S., & Kundu, T. (2011). Advanced DPSM approach for modeling ultrasonic wave scattering in an arbitrary geometry. Proceedings of SPIE - The International Society for Optical Engineering, 7984.
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  Abstract: Several techniques are used to diagnose structural damages. In the ultrasonic technique structures are tested by analyzing ultrasonic signals scattered by damages. The interpretation of these signals requires a good understanding of the interaction between ultrasonic waves and structures. Therefore, researchers need analytical or numerical techniques to have a clear understanding of the interaction between ultrasonic waves and structural damage. However, modeling of wave scattering phenomenon by conventional numerical techniques such as finite element method requires very fine mesh at high frequencies necessitating heavy computational power. Distributed point source method (DPSM) is a newly developed robust mesh free technique to simulate ultrasonic, electrostatic and electromagnetic fields. In most of the previous studies the DPSM technique has been applied to model two dimensional surface geometries and simple three dimensional scatterer geometries. It was difficult to perform the analysis for complex three dimensional geometries. This technique has been extended to model wave scattering in an arbitrary geometry. In this paper a channel section idealized as a thin solid plate with several rivet holes is formulated. The simulation has been carried out with and without cracks near the rivet holes. Further, a comparison study has been also carried out to characterize the crack. A computer code has been developed in C for modeling the ultrasonic field in a solid plate with and without cracks near the rivet holes. © 2011 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).
• Yadav, S. K., Banerjee, S., & Kundu, T. (2011). Effective damage sensitive feature extraction methods for crack detection using flaw scattered ultrasonic wave field signal. Structural Health Monitoring 2011: Condition-Based Maintenance and Intelligent Structures - Proceedings of the 8th International Workshop on Structural Health Monitoring, 1, 167-174.
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  Abstract: The structural damage detection and flaw characterization are being investigated by many researchers to evaluate the integrity of a structure. The ultrasonic wave field analysis is one of the foremost nondestructive evaluation techniques in this context because of its effectiveness and applicability in a variety of materials. However, the complex and chaotic nature of raw time domain ultrasonic signals makes it very difficult for any meaningful interpretation of the unprocessed time histories. The real challenge comes in extracting the damage information after analyzing large amount of such data. The time series investigations have been conducted using STFT, WT, CWD, Stockwell Transform, HHT, Winger-Ville, MP tools etc. and are being modified to calculate the most meaningful damage sensitive index. The techniques are being developed to analyze the ultrasonic data in time-frequency (TF) domain which ensures to address these issues by focusing mainly on critical damage sensitive features present in an ultrasonic signal. In the present study, different methods are formulated, analyzed and assessed comparatively to pin-point damage sensitive attributes out of Time-Frequency representation of the ultrasonic signal. A steel channel section with several rivet holes has been considered as a physical problem to be analyzed to generate ultrasonic wave field data. The simulation has been carried out by the finite element method for two cases - 1) a steel plate with cracks extending from the rivet holes and 2) an un-cracked structure. A MATLAB code has been developed for analyzing the FEM generated data.
• Yadav, S. K., Banerjee, S., & Kundu, T. (2011). On suitability of feature extraction techniques for local damage detection. Proceedings of SPIE - The International Society for Optical Engineering, 7983.
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  Abstract: Damage in the form of cracks near rivet holes in a steel channel section can be characterized by inspecting ultrasonic signals containing valuable information about these anomalies. Time-frequency representation (TFR) of time-history signal is an effective way to extract damage features out of an ultrasonic signal scattered from cracks. Several techniques are available to obtain Time-frequency representation and out of which feature extraction can be performed. However, every technique has its own advantages and disadvantage which makes it cumbersome to ascertain which specific technique is suitable to which specific problem. In present study, six TFR techniques e.g. Short Time Fourier Transform, Continuous Wavelet Transform, Wigner-Ville Spectrum, Hilbert-Huang Transform, Williams-Choi Transform and Stransform have been used to extract feature out of time-history signal obtained from finite element based wave scattering simulation of a plate with and without cracks near the rivet holes. Extracted damage features have been used to quantify the damage as a unique value by defining damage index formulation. Further, a comparison study has been carried out to assess these six techniques for their ability to give effective, reliable and consistent information about the cracks. Matlab codes have been developed to perform feature extraction and damage index calculation. © 2011 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).
• Ahmad, R., Kundu, T., & Placko, D. (2010). Modeling of the Ultrasonic Field of Two Transducers Immersed in a Homogenous Fluid Using the Distributed Point Source Method. Advanced Ultrasonic Methods for Material and Structure Inspection, 159-187.
• Amjad, U., Tarar, K. S., Shelke, A., Kundu, T., Pluta, M., & Grill, W. (2010). Generalized representations and universal aspects of Lamb wave dispersion relations. Proceedings of SPIE - The International Society for Optical Engineering, 7650(PART 1).
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  Abstract: Due to the dependence on a limited amount of parameters, the dispersion relations of Lamb waves can be presented in a generalized way. This is exemplified for the different established typical representations. Special attention is given to the representation of the momentum on energy, which is well suited to discuss basic features since energy as well as momentum is the properties which are strictly conserved in loss free homogeneous materials. Representations involving the phase and group velocity are discussed. Features related to level crossing of interacting modes and relations to basic mechanical properties especially relevant to Lamb waves are included in the presentation and discussion. © 2010 SPIE.
• Das, S., Banerjee, S., & Kundu, T. (2010). Transient ultrasonic wave field modeling in an elastic half-space using distributed point source method. Proceedings of SPIE - The International Society for Optical Engineering, 7650(PART 1).
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  Abstract: Transient ultrasonic waves in an elastic half-space generated by an ultrasonic transducer of finite size are modeled by the Distributed Point Source Method (DPSM). DPSM which is a Green's function based semi-analytical mesh-free technique is modified to incorporate the transient loading from a finite size acoustic transducer. Fast Fourier transform (FFT) of the transient loading is computed and then DPSM is used to compute the ultrasonic field at different frequencies and then inverse fast Fourier transform (IFFT) is taken to get the transient response of an elastic half-space excited by a bounded acoustic beam. Numerical results are generated for elastic half-space excited with normal incidence of acoustic beam. Then the transient Rayleigh wave in the solid half-space is generated. The modeling is then extended to the transient response of an elastic half-space containing a crack, struck by a bounded acoustic beam. It is discussed in the paper what type of useful information that is hidden in the steady state solution can be obtained from the transient results. © 2010 SPIE.
• Eskandarzade, M., Kundu, T., Liebeaux, N., Placko, D., & Mobadersani, F. (2010). Numerical simulation of electromagnetic acoustic transducers using distributed point source method. Ultrasonics, 50(6), 583-591.
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  PMID: 20071000;Abstract: In spite of many advances in analytical and numerical modeling techniques for solving different engineering problems, an efficient solution technique for wave propagation modeling of an electromagnetic acoustic transducer (EMAT) system is still missing. Distributed point source method (DPSM) is a newly developed semi-analytical technique developed since 2000 by Placko and Kundu (2007) [12] that is very powerful and straightforward for solving various engineering problems, including acoustic and electromagnetic modeling problems. In this study DPSM has been employed to model the Lorentz type EMAT with a meander line and flat spiral type coil. The problem of wave propagation has been solved and eddy currents and Lorentz forces have been calculated. The displacement field has been obtained as well. While modeling the Lorentz force the effect of dynamic magnetic field has been considered that most current analyses ignore. Results from this analysis have been compared with the finite element method (FEM) based predictions. It should be noted that with the current state of knowledge this problem can be solved only by FEM. © 2009 Elsevier B.V.
• Hajzargarbashi, T., Kundu, T., & Bland, S. (2010). A new algorithm for detecting impact point in anisotropic plates by the acoustic emission technique. Proceedings of SPIE - The International Society for Optical Engineering, 7650(PART 1).
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  Abstract: The wave speed in an anisotropic plate is dependent on the direction of propagation and therefore the conventional triangulation technique does not work for the prediction of the impact point. A method based on the optimization technique was proposed by Kundu et al. to detect the point of impact in an anisotropic plate. They defined an objective function that uses the time of flight information of the ultrasonic signals to the passive transducers attached to the plate and the wave propagation direction (θ) from the impact point to the receiving sensors. This function is very sensitive to the arrival times. A small variation in any one arrival time results in a significant change in the impact point prediction. This shortcoming is overcome here by modifying the objective function and following a new algorithm. Both old and new objective functions (denoted as functions 1 and 2) are used in the new algorithm. This algorithm uses different sets of transducers and identifies the common predictions from different sets. The proposed algorithm is less sensitive to the arrival time variation and thus is capable of predicting the impact point correctly even when the measured arrival time has some error. The objective function 2 is simpler, so the computer code run time is reduced and it is less likely to converge to the local minima when using the simplex or other optimization techniques. The theoretical predictions are compared with experimental results. © 2010 SPIE.
• Jata, K. V., Kundu, T., & Parthasarathy, T. A. (2010). An Introduction to Failure Mechanisms and Ultrasonic Inspection. Advanced Ultrasonic Methods for Material and Structure Inspection, 1-42.
• Kundu, T. (2010). Preface. Advanced Ultrasonic Methods for Material and Structure Inspection, xiii-xiv.
• Kundu, T. (2010). Proceedings of SPIE - The International Society for Optical Engineering: Introduction. Proceedings of SPIE - The International Society for Optical Engineering, 7650(PART 1), xix.
• Kundu, T., & Placko, D. (2010). Advanced Ultrasonic Methods for Material and Structure Inspection. Advanced Ultrasonic Methods for Material and Structure Inspection, 1-393.
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  Abstract: Ultrasonic signals are increasingly being used for predicting material behavior, both in an engineering context (detecting anomalies in a variety of structures) and a biological context (examining human bones, body parts and unborn fetuses). Featuring contributions from authors who are specialists in their subject area, this book presents new developments in ultrasonic research in both these areas, including ultrasonic NDE and other areas which go beyond traditional imaging techniques of internal defects. As such, both those in the biological and physical science communities will find this an informative and stimulating read. © 2007 ISTE Ltd.
• Kundu, T., Placko, D., Rahani, E. K., Yanagita, T., & Dao, C. M. (2010). Ultrasonic Field Modeling: A Comparison of Analytical, Semi-Analytical, and Numerical Techniques. IEEE TRANSACTIONS ON ULTRASONICS FERROELECTRICS AND FREQUENCY CONTROL, 57(12), 2795-2807.
• Kundu, T., Placko, D., Rahani, E. K., Yanagita, T., & Dao, C. M. (2010). Ultrasonic field modeling: A comparison of analytical, semi-analytical, and numerical techniques. IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, 57(12), 2795-2807.
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  PMID: 21156375;Abstract: Modeling ultrasonic fields in front of a transducer in the presence and absence of a scatterer is a fundamental problem that has been attempted by different techniques: analytical, semi-analytical, and numerical. However, a comprehensive comparison study among these techniques is currently missing in the literature. The objective of this paper is to make this comparison for different ultrasonic field modeling problems with various degrees of difficulty. Four fundamental problems are considered: a flat circular transducer, a flat square transducer, a circular concave transducer, and a point focused transducer (concave lens) in the presence of a cavity. The ultrasonic field in front of a finite-sized transducer can be obtained by Huygens-Fresnel superposition principle that integrates the contributions of several point sources distributed on the transducer face. This integral which is also known as the Rayleigh integral or Rayleigh-Sommerfeld integral (RSI) can be evaluated analytically for obtaining the pressure field variation along the central axis of the transducer for simple geometries, such as a flat circular transducer. The semi-analytical solution is a newly developed mesh-free technique called the distributed point source method (DPSM). The numerical solution is obtained from finite element analysis. Note that the first three problems study the effect of the transducer size and shape, whereas the fourth problem computes the field in presence of a scatterer. © 2010 IEEE.
• Kundu, T., Placko, D., Rahani, E. K., Yanagita, T., & Dao, C. M. (2010). Ultrasonic field modeling: A comparison of analytical, semi-analytical, and numerical techniques. IEEE transactions on ultrasonics, ferroelectrics, and frequency control, 57(12).
• Placko, D., Yanagita, T., Rahani, E. K., & Kundu, T. (2010). Mesh-free modeling of the interaction between a point-focused acoustic lens and a cavity. IEEE transactions on ultrasonics, ferroelectrics, and frequency control, 57(6).
• Placko, D., Yanagita, T., Rahani, E., & Kundu, T. (2010). Mesh-free modeling of the interaction between a point-focused acoustic lens and a cavity. IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, 57(6), 1396-1404.
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  PMID: 20529714;Abstract: Interaction between a cavity or void in a liquid and a converging ultrasonic beam generated by a point-focused acoustic lens is investigated. A semi-analytical technique called the distributed point source method (DPSM) is adopted because no analytical solution is available for this problem involving cavities of different size and the finite element method is not very efficient for modeling high-frequency ultrasonic problems. The solution shows that if the cavity is placed very close to the focal point of the lens then it can be detected by the acoustic lens. The detectability of the cavity at the off-focus position depends on the distance of the cavity from the focal point. The variation of this distance as the cavity moves in horizontal and vertical directions from the focal point is also investigated. © 2006 IEEE.
• Shelke, A., Das, S., & Kundu, T. (2010). Distributed point source method for modeling scattered ultrasonic fields in the presence of an elliptical cavity. Structural Health Monitoring, 9(6), 527-539.
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  Abstract: Scattering of ultrasonic waves by an elliptical cavity is modeled. The ratio of the semimajor to semiminor axes is varied from 1 to model a cylindrical cavity with a circular cross section to a large value to approximately model a Griffith crack. The distributed point source method (DPSM), which is a Green's function-based semi-analytical technique, is adapted in the present modeling. DPSM generated results for slit opening and elliptical cavity are compared. In the elliptical cavity model, the entire cavity surface is considered traction free, whereas in the slit model, two parallel crack surfaces are assumed traction free and no special consideration is given to the crack tips. Because a Griffith crack under tensile loads opens like an ellipse, the elliptical cavity with a large semimajor to semiminor axes ratio can be considered as an open Griffith crack. Elliptical cavity model clearly shows large stress values near the crack tips. Earlier DPSM models did not consider these high stress concentrations. The assumption was that it would have negligible effect on the scattering pattern at the far field. The numerical results are presented for a cavity of length 4 mm when bounded ultrasonic beams of 1 and 2.25 MHz frequency strike the solid half-space. © The Author(s), 2010.
• Shelke, A., Das, S., & Kundu, T. (2010). Distributed point source method for modeling scattered ultrasonic fields in the presence of an elliptical cavity. Structural health monitoring, 9(6), 527--539.
• Sourav, B., Samik, D., Kundu, T., Dao, C. M., Sourav, B., Samik, D., Kundu, T., & Dao, C. M. (2009). Wave Propagation In A Fluid Wedge Over A Solid Half-Space Mesh-Free Analysis with Experimental Verification. International Journal of Solids and Structures, 46, 2486-2492.
• Yadav, S., Banerjee, S., & Kundu, T. (2010). Local damage detection process for aging steel bridge joints. Proceedings of the 5th European Workshop - Structural Health Monitoring 2010, 1211-1216.
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  Abstract: Continuous health monitoring of aging civil infrastructure systems such as steel truss bridge is needed for proper maintenance and safety viewpoint. Use of piezoelectric sensors such as PZT (Lead Zirconate Titanate) is rapidly increasing in health monitoring systems of large structures. In active monitoring systems the structure under inspection is excited by PZT actuators. Actuator generated elastic waves are received by surface mounted or internal sensors and analyzed for damage detection. The objective of this study is to detect local damages in a steel bridge joints. So, a simple commonly occurring channel section with rivet holes has been investigated for the presence of cracks around the rivet holes by employing guided lamb waves. This understanding of PZT induced wave propagation in complex structures such as channel section containing cracked rivet holes is crucial for developing efficient damage detection algorithms in a steel bridge structure.
• Ahmad, R., Banerjee, S., & Kundu, T. (2009). Pipe wall damage detection in buried pipes using guided waves. Journal of Pressure Vessel Technology, Transactions of the ASME, 131(1).
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  Abstract: It is well known that cylindrical guided waves are very efficient for detecting pipe wall defects when pipes are open in the air. In this paper it is investigated how efficient the guided waves are for detecting pipe wall damage when the pipes are embedded in the soil. For this purpose guided waves were propagated through pipes that were buried in the soil by placing transmitters on one end of the embedded pipe and receivers on the other end. Received signals for both defect-free and defective pipes were recorded. Then the received signals were subjected to wavelet transforms. To investigate whether embedding the pipe in the soil makes it more difficult to detect the pipe wall defects, the same set of defective and defect-free pipes were studied before and after burying them in the soil. In both cases the defective pipes could be easily identified. Interestingly, contrary to the intuition, it was observed that under certain conditions defective pipes could be identified more easily in buried conditions. For example, the difference between the strengths of the initial parts of the received signal from defect-free and dented pipes was found to be greater for the buried pipes. Some qualitative justification for easier detection of buried dented pipes is provided. Copyright © 2009 by ASME.
• Ahmad, R., Banerjee, S., & Kundu, T. (2009). Pipe wall damage detection in buried pipes using guided waves. Journal of pressure vessel technology, 131(1), 011501.
• Banerjee, S., & Kundu, T. (2009). Modeling of energy transmission by piezoelectric wafer active sensors through gaussian contact. Proceedings of SPIE - The International Society for Optical Engineering, 7295.
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  Abstract: In present years, surface mounted piezoelectric wafer active sensors (PWAS) or piezoelectric patches are gaining popularity for onboard Structural Health Monitoring (SHM) systems. Through experimental investigations, it is apparent that several uncertainties are associated with the sensor signals. Proper understanding of the influence factors may provide insight to such uncertainties. Optimal placement of sensors is also a big challenge. In this paper, we have tried to report the pattern of wave field generated by the surface mounted actuators and the pattern of wave field developed near the sensors using a semi-analytical modeling technique called Distributed Point Source Method (DPSM). The surface mounted sensors/actuators are glued to the surface of the structure. Therefore, the contact between sensors and the host material is of utmost importance in transmitting energy into the host material. Long term interest of this research is to show the feature based differences in generated signals due to various types of contacts and debondings. However, in this paper we have addressed the most common type of contact called Gaussian contact which has a practical significance. In the near future, through this research, we can address issues related to other types of contact that frequently occur. This will help us to better understand the generated signals and quantify the uncertainties due to contact condition. © 2009 SPIE.
• Banerjee, S., Das, S., Kundu, T., & Placko, D. (2009). Controlled Space Radiation concept for mesh-free semi-analytical technique to model wave fields in complex geometries. Ultrasonics, 49(8), 615-622.
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  PMID: 19493555;Abstract: Numerical modelling of the ultrasonic wave propagation is important for Structural Heath Monitoring and System Prognosis problems. In order to develop intelligent and adaptive structures with embedded damage detector and classifier mechanisms, detailed understanding of scattered wave fields due to anomaly in the structure is inevitably required. A detailed understanding of the problem demands a good modelling of the wave propagation in the problem geometry in virtual form. Therefore, efficient analytical, semi-analytical or numerical modelling techniques are required. In recent years a semi-analytical mesh-free technique called Distributed Point Source Method (DPSM) is being used for modelling various ultrasonic, electrostatic and electromagnetic wave field problems. In the conventional DPSM approach point sources are placed along the transducer faces, problem boundaries and interfaces to model incident and scattered fields. Every point source emits energy in all directions uniformly. Source strengths of these 360° radiation sources are obtained by satisfying interface and boundary conditions of the problem. In conventional DPSM modelling approach it is assumed that the shadow zone does not require any special consideration. 360° Radiation point sources should be capable of properly modelling shadow zones because all boundary and interface conditions are satisfied. In this paper it is investigated how good this assumption is by introducing the 'shadow zone' concept at the point source level and comparing the results generated by the conventional DPSM and by this modified approach where the conventional 360° radiation point sources are replaced by the Controlled Space Radiation (CSR) sources. © 2009 Elsevier B.V. All rights reserved.
• Dao, C. M., Das, S., Banerjee, S., & Kundu, T. (2009). Wave propagation in a fluid wedge over a solid half-space - Mesh-free analysis with experimental verification. International Journal of Solids and Structures, 46(11-12), 2486-2492.
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  Abstract: Interaction between a bounded ultrasonic beam and a liquid wedge over a solid half-space is studied. A semi-analytical technique called distributed point source method (DPSM) is adopted for modeling the ultrasonic field in a wedge shaped fluid structure over a solid half space. This study is important for analyzing the ultrasonic waves used for the non-destructive inspections of partially immersed structures. It is also useful for studying the effect of underwater ultrasonic or acoustic wave experiments on marine lives near the shore. The problem geometry considers a bounded acoustic beam striking a fluid-solid interface between a fluid wedge and a solid half-space at steady-state. Solution of this problem is beyond the scope of the currently available analytical methods when the beam is bounded. Only numerical method (boundary element method (BEM) or finite element method (FEM)) based packages (e.g. PZFlex) are in principle capable of modeling ultrasonic fields in such structures. At high frequencies FEM and BEM based packages require huge amount of computation memory and time for their executions that DPSM technique can avoid. Effect of the angle of strike and the fluid wedge angle variation on the wave propagation characteristics is studied. Theoretical predictions are compared with some experimental results. © 2009 Elsevier Ltd. All rights reserved.
• Das, S., & Kundu, T. (2009). Mesh-free modeling of ultrasonic wave fields in damaged layered half-spaces. Structural Health Monitoring, 8(5), 369-379.
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  Abstract: Modeling of an ultrasonic wave field inside a layered half-space is carried out by using the mesh-free semi-analytical Distributed Point Source Method (DPSM). The complete field is computed in a layered half-space in presence and absence of defects. The layered structure is excited by a bounded ultrasonic beam generated by a finite-sized transducer. It is important to have theoretical models to predict the ultrasonic fields in damaged and damage-free structures for its nondestructive evaluation. Numerical exercises can be carried out aided by these theoretical models to determine the area of the most distorted ultrasonic field in presence of an internal anomaly. Several numerical examples are provided for an aluminum half-space attached to layers made of two different materials. The structure is excited by a bounded ultrasonic beam. Influence of the material properties and internal anomaly on the ultrasonic field pattern is demonstrated here. Copyright © SAGE Publications 2009.
• Das, S., & Kundu, T. (2009). Modeling of guided wave propagation in a layered half-space using distributed point source method. AIP Conference Proceedings, 1096, 177-184.
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  Abstract: Propagating guided waves in a layered half-space are modeled with the semi-analytical Distributed Point Source Method (DPSM). For nondestructive evaluation of solid structures using ultrasonic waves it is necessary to have an ultrasonic field model for the damage- free structure. This solution can be used as a baseline or benchmark solution. Any distortion in the ultrasonic field from this baseline should indicate the presence of one or more anomalies inside the structure. Distributed Point Source Method which is a Green's function based mesh-free technique is adopted here to generate the ultrasonic field inside the layer and the half-space when the layered structure is excited by an ultrasonic transducer of finite dimension. Unlike elastic half-space a layered half-space is a dispersive medium and several guided wave modes travel through the layer and the adjacent half-space. Numerical examples are given for an aluminum half-space attached to a layer made of a different material when the structure is excited by a bounded ultrasonic beam. It is also shown how the presence of an anomaly can influence the wave field inside the layered half- space. Displacements and stresses inside copper and epoxy layers and in the aluminum half-space are computed and presented as visual images. © 2009 American Institute of Physics.
• Ghosh, B., Chakraborty, P., Singh, B. P., & Kundu, T. (2009). Enhanced nonlinear optical responses in metal--glass nanocomposites. Applied surface science, 256(2), 389--394.
• Kundu, T. (2009). Proceedings of SPIE - The International Society for Optical Engineering: Introduction. Proceedings of SPIE - The International Society for Optical Engineering, 7295, XIX.
• Kundu, T., Das, S., & Jata, K. V. (2009). Detection of the point of impact on a stiffened plate by the acoustic emission technique. SMART MATERIALS AND STRUCTURES, 18(3).
• Kundu, T., Das, S., & Jata, K. V. (2009). Detection of the point of impact on a stiffened plate by the acoustic emission technique. Smart Materials and Structures, 18(3), 035006.
• Kundu, T., Das, S., & Jata, K. V. (2009). Detection of the point of impact on a stiffened plate by the acoustic emission technique. Smart Materials and Structures, 18(3).
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  Abstract: The applicability of guided waves to predict the point of impact in a stiffened plate is investigated. The conventional triangulation technique cannot predict the point of impact in a stiffened plate because the triangulation technique assumes that the wave speed is independent of the direction of propagation, which is not true for stiffened plates. An alternative method based on the optimization scheme was proposed by Kundu et al (2007J. Acoust. Soc. Am.1222057-66) to locate the point of impact in plates by analyzing the time of arrival of the ultrasonic signals received by passive sensors attached to the plate. After successful extension of this technique to predict the point of impact in anisotropic but homogeneous composite plates (Kundu et al 2008Ultrasonics48193-201) it is investigated in this paper whether this technique works well for predicting the point of impact in an inhomogeneous plate where the stiffeners make the structure inhomogeneous. Experiments are carried out by dropping ping pong and metal balls on the plate to simulate the impact phenomenon and recording acoustic signals by passive transducers adhesively bonded to the plate at three different locations. The impact points are predicted and compared with the actual locations of impact. © 2009 IOP Publishing Ltd.
• Kundu, T., Das, S., & Jata, K. V. (2009). Health monitoring of a thermal protection system using lamb waves. Structural Health Monitoring, 8(1), 29-45.
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  Abstract: The applicability of guided waves as a structural health monitoring (SHM) tool to predict the point of impact and detect delamination in a thermal protection system (TPS) is studied. A model TPS was designed by bonding ceramic porous tiles to a 2.2 mm thick 2124-T351 aluminum alloy plate. The delamination defect may be caused by the impact phenomenon or due to other reasons such as manufacturing defect, thermal, or mechanical fatigue, etc. Impact phenomenon is simulated by dropping a ping pong ball on the tiled structure. The delamination at the interface between the ceramic tile and the aluminum plate is simulated by removing the adhesive bond at the selected interface regions during the specimen fabrication process. The conventional triangulation technique cannot predict the point of impact in a tiled plate structure because the triangulation technique assumes that the wave speed is independent of the direction of propagation which is not the case for ceramic tile mounted plates. An alternative method based on the optimization scheme was proposed by Kundu et al. to locate the point of impact in plates by analyzing the time of arrival of the ultrasonic signals received by passive sensors attached to the plate. This objective function based method is used to locate the impact point on the tiled plate. Experiments are carried out by dropping a ping pong ball on the tiled structure and recording acoustic signals by passive transducers adhesively bonded to the plate at three different locations. The impact point is predicted and compared with the actual location of impact. Delamination detection studies were conducted in the pitch-catch mode, by changing the angle of strike and the frequency of the transducer excitation to generate the appropriate guided wave mode. The delamination defect could be detected and the impact point could be identified underlining the importance of the use of guided waves as an SHM tool for TPS. © SAGE Publications 2009.
• Kundu, T., Placko, D., Yanagita, T., & Sathish, S. (2009). Micro interferometric acoustic lens: Mesh-free modeling with experimental verification. Proceedings of SPIE - The International Society for Optical Engineering, 7295.
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  Abstract: The ultrasonic field generated by a Micro Intereferometric Acoustic Lens used for high precision Rayleigh wave velocity measurements is modeled by the recently developed mesh-free technique called Distributed Point Source Method (DPSM). The field generated by the three individual ultrasonic transducer elements forming the micro intereferometric acoustic lens are computed and compared with experimental measurements. Qualitative agreement between the theoretical and experimental results is observed; both results show converging beams up to the focal point and then the beams diverge. However, some of the minute detailed features in the generated ultrasonic field could only be observed in the computed results. Effects of non-uniform surface of the transducer and its contribution to the non-uniform ultrasonic source strength are investigated to understand and optimize the acoustic lens for localized quantitative elastic property measurements. © 2009 SPIE.
• Malinowski, P., Wandowski, T., Trendafilova, I., & Ostachowicz, W. (2009). A phased array-based method for damage detection and localization in thin plates. Structural Health Monitoring, 8(1), 5--15.
• Yanagita, T., Kundu, T., & Placko, D. (2009). Ultrasonic field modeling by distributed point source method for different transducer boundary conditions. Journal of the Acoustical Society of America, 126(5), 2331-2339.
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  PMID: 19894816;Abstract: Several investigators have modeled ultrasonic fields in front of transducers by Huygens-Fresnel superposition principle that integrates the contributions of a number of point sources distributed on the transducer face. This integral solution, also known as the Rayleigh integral or Rayleigh-Sommerfeld Integral solution, assumes the strengths of the point sources distributed over the transducer face. A newly developed technique called distributed point source method (DPSM) offers an alternative approach for modeling ultrasonic fields. DPSM is capable of modeling the field for prescribed source strength distribution as well as for prescribed interface conditions with unknown source strengths. It is investigated how the ultrasonic field in front of the transducer varies in different situations: (1) when the point source strengths are known, (2) when the point source strengths are unknown but obtained from the interface condition that only the normal component of the transducer velocity is continuous across the fluid-solid interface, (3) when all three components of velocity are assumed to be continuous across the interface for the no-slip condition, and (4) when the pressure instead of the velocity is prescribed on the transducer face. Results for these different interface conditions are compared with the analytical solutions along the central axis. © 2009 Acoustical Society of America.
• Akhras, G., Asanuma, H., Balageas, D., Bannister, M., Boller, C., Buderath, M., Budelmann, H., Casas, J. R., Casciati, F., Caussignac, J. -., Cawley, P., Chang, F. -., Culshaw, B., Déom, A., Fassois, S., Fernando, G., Fritzen, C. -., Gabbert, U., Giurgiutiu, V., , Gobin, P. -., et al. (2008). Proceedings of the 4th European Workshop on Structural Health Monitoring: Preface. Proceedings of the 4th European Workshop on Structural Health Monitoring, xvii-xix.
• Akhtar, R., Sherratt, M. J., E., R., Kundu, T., & Derby, B. (2008). Mapping the micromechanical properties of cryo-sectioned aortic tissue with Scanning Acoustic Microscopy. Materials Research Society Symposium Proceedings, 1133, 120-125.
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  Abstract: Although the gross mechanical properties of ageing tissues have been extensively documented, biological tissues are highly heterogeneous and little is known concerning the variation of micro-mechanical properties within tissues. Here, we use Scanning Acoustic Microscopy (SAM) to map the acoustic wave speed (a measure of stiffness) as a function of distance from the outer adventitial layer of cryo-sectioned ferret aorta. With a 400 MHz lens, the images of the aorta samples matched those obtained following chemical fixation and staining of sections which were viewed with fluorescence microscopy. Quantitative analysis was conducted with a frequency scanning or V(f) technique by imaging the tissue from 960 MHz to 1.1 GHz. Undulating acoustic wave speed (stiffness) distributions corresponded with elastic fibre locations in the tissue; there was a decrease in wave speed of around 40 ms-1 from the adventitia (outer layer) to the intima (innermost). © 2009 Materials Research Society.
• Akhtar, R., Sherratt, M. J., E., R., Kundu, T., & Derby, B. (2008). Mapping the micromechanical properties of cryo-sectioned aortic tissue with Scanning Acoustic Microscopy. Materials Research Society Symposium Proceedings, 1135, 62-67.
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  Abstract: Although the gross mechanical properties of ageing tissues have been extensively documented, biological tissues are highly heterogeneous and little is known concerning the variation of micro-mechanical properties within tissues. Here, we use Scanning Acoustic Microscopy (SAM) to map the acoustic wave speed (a measure of stiffness) as a function of distance from the outer adventitial layer of cryo-sectioned ferret aorta. With a 400 MHz lens, the images of the aorta samples matched those obtained following chemical fixation and staining of sections which were viewed with fluorescence microscopy. Quantitative analysis was conducted with a frequency scanning or V(f) technique by imaging the tissue from 960 MHz to 1.1 GHz. Undulating acoustic wave speed (stiffness) distributions corresponded with elastic fibre locations in the tissue; there was a decrease in wave speed of around 40 ms-1 from the adventitia (outer layer) to the intima (innermost). © 2009 Materials Research Society.
• Akhtar, R., Sherratt, M. J., E., R., Kundu, T., & Derby, B. (2008). Mapping the micromechanical properties of cryo-sectioned aortic tissue with Scanning Acoustic Microscopy. Materials Research Society Symposium Proceedings, 1136, 53-58.
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  Abstract: Although the gross mechanical properties of ageing tissues have been extensively documented, biological tissues are highly heterogeneous and little is known concerning the variation of micro-mechanical properties within tissues. Here, we use Scanning Acoustic Microscopy (SAM) to map the acoustic wave speed (a measure of stiffness) as a function of distance from the outer adventitial layer of cryo-sectioned ferret aorta. With a 400 MHz lens, the images of the aorta samples matched those obtained following chemical fixation and staining of sections which were viewed with fluorescence microscopy. Quantitative analysis was conducted with a frequency scanning or V(f) technique by imaging the tissue from 960 MHz to 1.1 GHz. Undulating acoustic wave speed (stiffness) distributions corresponded with elastic fibre locations in the tissue; there was a decrease in wave speed of around 40 ms-1 from the adventitia (outer layer) to the intima (innermost). © 2009 Materials Research Society.
• Akhtar, R., Sherratt, M. J., E., R., Kundu, T., & Derby, B. (2008). Mapping the micromechanical properties of cryo-sectioned aortic tissue with Scanning Acoustic Microscopy. Materials Research Society Symposium Proceedings, 1146, 66-71.
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  Abstract: Although the gross mechanical properties of ageing tissues have been extensively documented, biological tissues are highly heterogeneous and little is known concerning the variation of micro-mechanical properties within tissues. Here, we use Scanning Acoustic Microscopy (SAM) to map the acoustic wave speed (a measure of stiffness) as a function of distance from the outer adventitial layer of cryo-sectioned ferret aorta. With a 400 MHz lens, the images of the aorta samples matched those obtained following chemical fixation and staining of sections which were viewed with fluorescence microscopy. Quantitative analysis was conducted with a frequency scanning or V(f) technique by imaging the tissue from 960 MHz to 1.1 GHz. Undulating acoustic wave speed (stiffness) distributions corresponded with elastic fibre locations in the tissue; there was a decrease in wave speed of around 40 ms -1 from the adventitia (outer layer) to the intima (innermost). © 2009 Materials Research Society.
• Akhtar, R., Sherratt, M. J., E., R., Kundu, T., & Derby, B. (2008). Mapping the micromechanical properties of cryo-sectioned aortic tissue with scanning acoustic microscopy. Materials Research Society Symposium Proceedings, 1145, 195-200.
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  Abstract: Although the gross mechanical properties of ageing tissues have been extensively documented, biological tissues are highly heterogeneous and little is known concerning the variation of micro-mechanical properties within tissues. Here, we use Scanning Acoustic Microscopy (SAM) to map the acoustic wave speed (a measure of stiffness) as a function of distance from the outer adventitial layer of cryo-sectioned ferret aorta. With a 400 MHz lens, the images of the aorta samples matched those obtained following chemical fixation and staining of sections which were viewed with fluorescence microscopy. Quantitative analysis was conducted with a frequency scanning or V(f) technique by imaging the tissue from 960 MHz to 1.1 GHz. Undulating acoustic wave speed (stiffness) distributions corresponded with elastic fibre locations in the tissue; there was a decrease in wave speed of around 40 ms-1 from the adventitia (outer layer) to the intima (innermost). © 2009 Materials Research Society.
• Akhtar, R., Sherratt, M. J., E., R., Kundu, T., & Derby, B. (2008). Mapping the micromechanical properties of cryo-sectioned aortic tissue with scanning acoustic microscopy. Materials Research Society Symposium Proceedings, 1152, 115-120.
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  Abstract: Although the gross mechanical properties of ageing tissues have been extensively documented, biological tissues are highly heterogeneous and little is known concerning the variation of micro-mechanical properties within tissues. Here, we use Scanning Acoustic Microscopy (SAM) to map the acoustic wave speed (a measure of stiffness) as a function of distance from the outer adventitial layer of cryo-sectioned ferret aorta. With a 400 MHz lens, the images of the aorta samples matched those obtained following chemical fixation and staining of sections which were viewed with fluorescence microscopy. Quantitative analysis was conducted with a frequency scanning or V(f) technique by imaging the tissue from 960 MHz to 1.1 GHz. Undulating acoustic wave speed (stiffness) distributions corresponded with elastic fibre locations in the tissue; there was a decrease in wave speed of around 40 ms-1 from the adventitia (outer layer) to the intima (innermost). © 2009 Materials Research Society.
• Akhtar, R., Sherratt, M. J., Watson, R. E., Kundu, T., & Derby, B. (2008). Mapping the micromechanical properties of cryo-sectioned aortic tissue with scanning acoustic microscopy. MRS Online Proceedings Library Archive, 1132.
• Akhtar, R., Sherratt, M. J., Watson, R. E., Kundu, T., & Derby, B. (2008). Mapping the micromechanical properties of cryo-sectioned aortic tissue with scanning acoustic microscopy. Materials Research Society Symposium Proceedings, 1132, 41-46.
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  Abstract: Although the gross mechanical properties of ageing tissues have been extensively documented, biological tissues are highly heterogeneous and little is known concerning the variation of micro-mechanical properties within tissues. Here, we use Scanning Acoustic Microscopy (SAM) to map the acoustic wave speed (a measure of stiffness) as a function of distance from the outer adventitial layer of cryo-sectioned ferret aorta. With a 400 MHz lens, the images of the aorta samples matched those obtained following chemical fixation and staining of sections which were viewed with fluorescence microscopy. Quantitative analysis was conducted with a frequency scanning or V(f) technique by imaging the tissue from 960 MHz to 1.1 GHz. Undulating acoustic wave speed (stiffness) distributions corresponded with elastic fibre locations in the tissue; there was a decrease in wave speed of around 40 ms-1 from the adventitia (outer layer) to the intima (innermost). © 2009 Materials Research Society.
• Akhtar, R., Sherratt, M. J., Watson, R. E., Kundu, T., & Derby, B. (2008). Mapping the micromechanical properties of cryo-sectioned aortic tissue with scanning acoustic microscopy. Materials Research Society Symposium Proceedings, 1151, 79-84.
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  Abstract: Although the gross mechanical properties of ageing tissues have been extensively documented, biological tissues are highly heterogeneous and little is known concerning the variation of micro-mechanical properties within tissues. Here, we use Scanning Acoustic Microscopy (SAM) to map the acoustic wave speed (a measure of stiffness) as a function of distance from the outer adventitial layer of cryo-sectioned ferret aorta. With a 400 MHz lens, the images of the aorta samples matched those obtained following chemical fixation and staining of sections which were viewed with fluorescence microscopy. Quantitative analysis was conducted with a frequency scanning or V(f) technique by imaging the tissue from 960 MHz to 1.1 GHz. Undulating acoustic wave speed (stiffness) distributions corresponded with elastic fibre locations in the tissue; there was a decrease in wave speed of around 40 ms-1 from the adventitia (outer layer) to the intima (innermost). © 2009 Materials Research Society.
• Banerjee, S., & Kundu, T. (2008). Elastic wave field computation in multilayered nonplanar solid structures: A mesh-free semianalytical approach. Journal of the Acoustical Society of America, 123(3), 1371-1382.
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  PMID: 18345826;Abstract: Multilayered solid structures made of isotropic, transversely isotropic, or general anisotropic materials are frequently used in aerospace, mechanical, and civil structures. Ultrasonic fields developed in such structures by finite size transducers simulating actual experiments in laboratories or in the field have not been rigorously studied. Several attempts to compute the ultrasonic field inside solid media have been made based on approximate paraxial methods like the classical ray tracing and multi-Gaussian beam models. These approximate methods have several limitations. A new semianalytical method is adopted in this article to model elastic wave field in multilayered solid structures with planar or nonplanar interfaces generated by finite size transducers. A general formulation good for both isotropic and anisotropic solids is presented in this article. A variety of conditions have been incorporated in the formulation including irregularities at the interfaces. The method presented here requires frequency domain displacement and stress Green's functions. Due to the presence of different materials in the problem geometry various elastodynamic Green's functions for different materials are used in the formulation. Expressions of displacement and stress Green's functions for isotropic and anisotropic solids as well as for the fluid media are presented. Computed results are verified by checking the stress and displacement continuity conditions across the interface of two different solids of a bimetal plate and investigating if the results for a corrugated plate with very small corrugation match with the flat plate results. © 2008 Acoustical Society of America.
• Banerjee, S., & Kundu, T. (2008). Semi-analytical modeling of ultrasonic fields in solids with internal anomalies immersed in a fluid. Wave Motion, 45(5), 581-595.
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  Abstract: Modeling of ultrasonic fields in presence of cracks, inclusions and delaminations in materials is of great interest to the researchers in the field of real time non-destructive evaluation (NDE) and structural health monitoring (SHM). Ultrasonic fields generated by finite size transducers in various structures with cracks and inclusions simulating actual experiments have been studied by numerical and semi-analytical techniques. However, many of the semi-analytical techniques lack simple implementation for complex structure geometries and numerical techniques often suffer from accuracy problems at high frequencies. Several attempts to compute the ultrasonic fields inside solid media have been made based on approximate paraxial methods such as the classical ray-tracing and multi-Gaussian beam models. These approximate methods have several limitations. A new semi-analytical method is adopted in this paper to model elastic wave fields in half-space and plate structures with internal anomalies generated by finite size transducers. A general formulation good for both isotropic and anisotropic solids is presented in this paper. No simplifying assumption has been made on the geometry of the anomalies. Therefore, the formulation presented in this paper can be applied to anomalies with any geometry. © 2007 Elsevier B.V. All rights reserved.
• Dao, C. M., Das, S., Banerjee, S., & Kundu, T. (2008). Bounded acoustic beam in a fluid wedge over a solid half space: Acombined theoretical/experimental investigation. AIP Conference Proceedings, 975, 115-122.
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  Abstract: Interaction between a bounded acoustic beam and a fluid wedge over a solid half space is studied. Nondestructive evaluation of partially immersed solids requires such investigations. Solution of this problem is beyond the scope of the currently available analytical methods. FEM based numerical techniques are also not very efficient for solving high-frequency ultrasonic problems. A newly developed semi-analytical technique called Distributed Point Source Method is used to solve this problem. Theoretical predictions are experimentally verified. © 2008 American Institute of Physics.
• Das, S., Banerjee, S., & Kundu, T. (2008). Elastic wave scattering in a solid half-space with a circular cylindrical hole using the Distributed Point Source Method. International Journal of Solids and Structures, 45(16), 4498-4508.
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  Abstract: Ultrasonic wave scattering in a solid half-space containing a circular cylindrical hole is studied. The solid is struck by a bounded ultrasonic beam. Distributed Point Source Method (DPSM) which is a semi-analytical technique is adopted to model the ultrasonic field. A finite size transducer is used to generate the ultrasonic field. The circular hole in the solid is modeled by passive point sources. These point sources along with the point sources placed near the fluid-solid interface contribute to the scattered wave field in the solid. Even though the wave scattering by a circular hole in a solid is a classical problem this is the first time the complete variation of the scattered wave field generated by a bounded ultrasonic beam in a solid half-space with a circular hole is shown. The solution of this problem will help us to understand the distortion of the ultrasonic field in a solid and in the neighboring fluid due to the presence of a cylindrical anomaly which plays an important role in sensitivity analysis and calibration of different non-destructive testing techniques. Numerical examples for 1 MHz and 2.25 MHz transducers are given and scattered wave fields generated by holes of different diameters in an aluminum half-space are compared with the wave fields generated in the defect-free environment. © 2008 Elsevier Ltd. All rights reserved.
• Das, S., Banerjee, S., & Kundu, T. (2008). Modeling of elastic wave scattering by a hole in a half-space. Proceedings of SPIE - The International Society for Optical Engineering, 6935.
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  Abstract: In NDT (nondestructive testing) often a side-drilled hole (circular cavity) is used for calibration. In this paper scattering of ultrasonic waves by a circular hole is studied. The ultrasonic wave is generated by a transducer of finite dimension. A newly developed semi-analytical technique called Distributed point source method (DPSM) has been adopted to solve this problem. Even though this is an old problem the complete field of the scattered waves in presence of a hole in a half space near its boundary has not been shown in the literature yet. The scattered ultrasonic field (stress and displacement) is computed using DPSM and presented in the paper. Solution of this problem will also help us to understand the distortion of the ultrasonic field in the half-space due to the presence of a circular anomaly (cavity or inclusion) which plays an important role in structural health monitoring.
• Kundu, T. (2008). Proceedings of SPIE - The International Society for Optical Engineering: Introduction. Proceedings of SPIE - The International Society for Optical Engineering, 6935, xvii.
• Kundu, T., Banerjee, S., & Kundu, T. -. (2008). Elastic wave field computation in multilayered nonplanar solid structures: a mesh-free semianalytical approach. The Journal of the Acoustical Society of America, 123(3).
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  Multilayered solid structures made of isotropic, transversely isotropic, or general anisotropic materials are frequently used in aerospace, mechanical, and civil structures. Ultrasonic fields developed in such structures by finite size transducers simulating actual experiments in laboratories or in the field have not been rigorously studied. Several attempts to compute the ultrasonic field inside solid media have been made based on approximate paraxial methods like the classical ray tracing and multi-Gaussian beam models. These approximate methods have several limitations. A new semianalytical method is adopted in this article to model elastic wave field in multilayered solid structures with planar or nonplanar interfaces generated by finite size transducers. A general formulation good for both isotropic and anisotropic solids is presented in this article. A variety of conditions have been incorporated in the formulation including irregularities at the interfaces. The method presented here requires frequency domain displacement and stress Green's functions. Due to the presence of different materials in the problem geometry various elastodynamic Green's functions for different materials are used in the formulation. Expressions of displacement and stress Green's functions for isotropic and anisotropic solids as well as for the fluid media are presented. Computed results are verified by checking the stress and displacement continuity conditions across the interface of two different solids of a bimetal plate and investigating if the results for a corrugated plate with very small corrugation match with the flat plate results.
• Kundu, T., Banerjee, S., Das, S., & Dao, C. M. (2008). Recent developments in theoretical and experimental investigations with ultrasonic sensors. Proceedings of the World Forum on Smart Materials and Smart Structures Technology, SMSST'07, 330-.
• Kundu, T., Das, S., & Jata, K. V. (2008). Point of impact prediction in anisotropic fiber reinforced composite plates from the acoustic emission data. AIP Conference Proceedings, 975, 1405-1412.
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  Abstract: A newly developed optimization based method is followed to locate the point of impact in anisotropic composite plates for which conventional triangulation technique fails. The new technique works for both anisotropic and isotropic plates. Experiments are carried out by dropping a steel ball on a graphite-epoxy composite plate and picking up acoustic signals by passive transducers adhesively bonded to the plate at different locations. Predicted points of impact are compared with the true impact point. © 2008 American Institute of Physics.
• Kundu, T., Das, S., Martin, S. A., & Jata, K. V. (2008). Locating point of impact in anisotropic fiber reinforced composite plates. ULTRASONICS, 48(3), 193-201.
• Kundu, T., Das, S., Martin, S. A., & Jata, K. V. (2008). Locating point of impact in anisotropic fiber reinforced composite plates. Ultrasonics, 48(3), 193-201.
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  PMID: 18255117;Abstract: The conventional triangulation technique cannot predict the point of impact in an anisotropic composite plate because the triangulation technique assumes that the wave speed is independent of the direction of propagation which is not the case for anisotropic plates. An alternative method based on the optimization scheme was proposed by Kundu et al. [T. Kundu, S. Das, K.V. Jata, Point of impact prediction in isotropic and anistropic plates from the acoustic emission data, J. Acoust. Soc. Am. 122, 2007, 2057-2066] to locate the point of impact in plates by analyzing the time of arrival of the ultrasonic signals received by the passive sensors attached to the plate. In this paper, that objective function is modified further to overcome the inherent difficulties associated with multiple singularities and to maximize the efficiency of the acoustic emission data for multiple receiving sensors. With this modified objective function the impact point on an anisotropic composite plate is predicted from the acoustic emission data. Experiments are carried out by dropping steel and ping pong balls on a graphite-epoxy composite plate and recording acoustic signals by passive transducers adhesively bonded to the plate at three different locations. The impact point is predicted by the proposed method and compared with the actual location of impact. © 2007 Elsevier B.V. All rights reserved.
• Vasiljevic, M., Kundu, T., Grill, W., & Twerdowski, E. (2008). Pipe wall damage detection by electromagnetic acoustic transducer generated guided waves in absence of defect signals. Journal of the Acoustical Society of America, 123(5), 2591-2597.
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  PMID: 18529178;Abstract: Most investigators emphasize the importance of detecting the reflected signal from the defect to determine if the pipe wall has any damage and to predict the damage location. However, often the small signal from the defect is hidden behind the other arriving wave modes and signal noise. To overcome the difficulties associated with the identification of the small defect signal in the time history plots, in this paper the time history is analyzed well after the arrival of the first defect signal, and after different wave modes have propagated multiple times through the pipe. It is shown that the defective pipe can be clearly identified by analyzing these late arriving diffuse ultrasonic signals. Multiple reflections and scattering of the propagating wave modes by the defect and pipe ends do not hamper the defect detection capability; on the contrary, it apparently stabilizes the signal and makes it easier to distinguish the defective pipe from the defect-free pipe. This paper also highlights difficulties associated with the interpretation of the recorded time histories due to mode conversion by the defect. The design of electro-magnetic acoustic transducers used to generate and receive the guided waves in the pipe is briefly described in the paper. © 2008 Acoustical Society of America.
• Vasiljevic, M., Kundu, T., Grill, W., & Twerdowski, E. (2008). Recent advances on pipe inspection using guided waves generated by electromagnetic acoustic transducers. Proceedings of SPIE - The International Society for Optical Engineering, 6935.
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  Abstract: For several years guided waves have been used for pipe wall defect detection. Guided waves have become popular for monitoring large structures because of the capability of these waves to propagate long distances along pipes, plates, interfaces and structural boundaries before loosing their strengths. The current technological challenges are to detect small defects in the pipe wall and estimate their dimensions using appropriate guided wave modes and to generate those modes relatively easily for field applications. Electro-Magnetic Acoustic Transducers (EMAT) can generate guided waves in pipes in the field environment. This paper shows how small defects in the pipe wall can be detected and their dimensions can be estimated by appropriate signal processing technique applied to the signals generated and received by the EMAT.
• Yanagita, T., Placko, D., & Kundu, T. (2008). Effect of transducer boundary conditions on the generated ultrasonic field. Proceedings of SPIE - The International Society for Optical Engineering, 6935.
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  Abstract: Several investigators have modeled ultrasonic fields in front of finite sized transducers. Most of these models are based on Huygens principle. Following Huygens-Fresnel superposition principle one can assume that the total field of a finite size transducer is obtained by simply superimposing the contributions of a number of point sources uniformly distributed on the transducer face. If the point source solution, also known as the Green's function, is known then integrating that point source solution over the transducer face one can obtain the total ultrasonic field generated by a finite transducer. This integral is known as Rayleigh-Sommerfield integral. It is investigated here how the ultrasonic field in front of the transducer varies for different interface conditions at the transducer face-fluid interface such as 1) when only the normal component of the transducer velocity is assumed to be uniform on the transducer face and continuous across the fluid-solid interface, or 2) when all three components of velocity are assumed to be uniform on the transducer face and continuous across the interface, 3) when the pressure instead of velocity is assumed to be uniform on the transducer face and continuous across the interface. AU these different boundary and interface conditions can be modeled by the newly developed Distributed Point Source Method (DPSM). These results are compared with the Rayleigh-Sommerfield integral representation that gives the fluid pressure in front of the transducer when the transducer-fluid interface is subjected to uniform normal velocity.
• Ahmad, R., & Kundu, T. (2007). Application of Gabor transform on cylindrical guided waves to detect defects in underground pipes. Proceedings of SPIE - The International Society for Optical Engineering, 6532.
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  Abstract: Defects in underground pipes are detected by applying Gabor transforms on experimental guided wave signals and comparing the experimental group velocity plots with the theoretical group velocity dispersion curves. Gabor transform, which is a powerful signal processing tool, maps a signal into a two-dimensional space of time and frequency. Thus it provides information about both when and at what frequency a signal arrives. Focus of this paper is to study the applicability of cylindrical guided waves to detect defects in underground pipes using Gabor transform. Cylindrical guided waves are generated by piezo-electric transducers. Guided waves are propagated through pipes that are buried in the soil by placing transmitters on one end of the pipes and the receivers on the other end. The recorded signals are then processed using 2-D Gabor Transform or Short Time Fourier Transform (STFT). Gabor transform converts the timeamplitude signal into a time frequency signal which reveals the group velocities hidden in the signal. These experimentally obtained group velocities are then compared with the theoretical velocities for cylindrical pipes embedded in the soil. From the comparison of the theoretical and experimental group velocities, an effort has been made to identify which modes are propagating through the embedded defective pipes and which modes are having difficulty to propagate through the defective pipe wall. From this knowledge pipe wall defects can be detected.
• Ahmad, R., Kundu, T., & Placko, D. (2007). Modeling of the Ultrasonic Field of Two Transducers Immersed in a Homogenous Fluid Using the Distributed Point Source Method. Advanced Ultrasonic Methods for Material and Structure Inspection, 159--187.
• Banerjee, S., & Kundu, T. (2007). Advanced applications of distributed point source method-ultrasonic field modeling in solid media. DPSM for Modeling Engineering Problems, 143--229.
• Banerjee, S., & Kundu, T. (2007). Modeling ultrasonic wave scattering by internal anomalies for structural monitoring. SPIE Newsroom.
• Banerjee, S., & Kundu, T. (2007). Scattering of ultrasonic waves by internal anomalies in plates. Optical Engineering, 46(5), 053601.
• Banerjee, S., & Kundu, T. (2007). Scattering of ultrasonic waves by internal anomalies in plates. Optical Engineering, 46(5).
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  Abstract: Real-time nondestructive testing (NDT) and nondestructive evaluation (NDE) of plate-type structures are important for structural health monitoring (SHM) applications. In this work, the wave scattering from horizontally oriented internal cavities or cracks in a plate is studied using the distributed point source method (DPSM). DPSM has gained popularity in the last few years in the field of ultrasonic field modeling. DPSM is a semianalytical technique that can be used to calculate the ultrasonic field (pressure, velocity, and displacement fields in a fluid, or stress and displacement fields in a solid) generated by ultrasonic transducers. So far, the technique has been used to model the ultrasonic field near a fluid-solid interface when a solid half-space is immersed in a fluid. This method has also been used to model the ultrasonic field generated in a homogeneous isotropic solid plate immersed in a fluid. The objective of this study is to present the theoretical modeling of the diffraction and scattering pattern of guided waves in the solid plate when transducers of finite dimension are used to generate guided waves in the defective plate. © 2007 Society of Photo-Optical Instrumentation Engineers.
• Banerjee, S., & Kundu, T. (2007). Ultrasonic field modeling in plates immersed in fluid. INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES, 44(18-19), 6013-6029.
• Banerjee, S., & Kundu, T. (2007). Ultrasonic field modeling in plates immersed in fluid. International Journal of Solids and Structures, 44(18-19), 6013-6029.
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  Abstract: Distributed Point Source Method (DPSM) is a semi-analytical technique that can be used to calculate the ultrasonic field (pressure, velocity and displacement fields in a fluid, or stress and displacement fields in a solid) generated by ultrasonic transducers. So far the technique has been used to model ultrasonic fields in homogeneous and multilayered fluid structures, and near a fluid-solid interface when a solid half-space is immersed in a fluid. In this paper, the method is extended to model the ultrasonic field generated in a homogeneous isotropic solid plate immersed in a fluid. The objective of this study is to model the generation of guided waves in a solid plate when ultrasonic beams from transducers of finite dimension strike the plate at different critical angles. DPSM results for a solid half-space problem are compared with the finite element predictions to show the superiority of the DPSM technique. The predicted results are also compared with the experimental visualization of the mode patterns of Lamb waves propagating in a glass plate obtained from stroboscopic photoelastic method. Experimental and theoretical results show good qualitative agreement. The DPSM technique is then applied to study the mode patterns in aluminum plates immersed in water. © 2007 Elsevier Ltd. All rights reserved.
• Banerjee, S., Kundu, T., & Alnuaimi, N. A. (2007). DPSM technique for ultrasonic field modelling near fluid-solid interface. Ultrasonics, 46(3), 235-250.
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  PMID: 17397891;Abstract: Distributed point source method (DPSM) is gradually gaining popularity in the field of non-destructive evaluation (NDE). DPSM is a semi-analytical technique that can be used to calculate the ultrasonic fields produced by transducers of finite dimension placed in homogeneous or non-homogeneous media. This technique has been already used to model ultrasonic fields in homogeneous and multi-layered fluid structures. In this paper the method is extended to model the ultrasonic fields generated in both fluid and solid media near a fluid-solid interface when the transducer is placed in the fluid half-space near the interface. Most results in this paper are generated by the newly developed DPSM technique that requires matrix inversion. This technique is identified as the matrix inversion based DPSM technique. Some of these results are compared with the results produced by the Rayleigh-Sommerfield integral based DPSM technique. Theory behind both matrix inversion based and Rayleigh-Sommerfield integral based DPSM techniques is presented in this paper. The matrix inversion based DPSM technique is found to be very efficient for computing the ultrasonic field in non-homogeneous materials. One objective of this study is to model ultrasonic fields in both solids and fluids generated by the leaky Rayleigh wave when finite size transducers are inclined at Rayleigh critical angles. This phenomenon has been correctly modelled by the technique. It should be mentioned here that techniques based on paraxial assumptions fail to model the critical reflection phenomenon. Other advantages of the DPSM technique compared to the currently available techniques for transducer radiation modelling are discussed in the paper under Introduction. © 2007 Elsevier B.V. All rights reserved.
• Banerjee, S., Kundu, T., & Placko, D. (2007). An improved DPSM technique for modelling ultrasonic fields in cracked solids. Proceedings of SPIE - The International Society for Optical Engineering, 6532.
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  Abstract: In recent years Distributed Point Source Method (DPSM) is being used for modelling various ultrasonic, electrostatic and electromagnetic field modelling problems. In conventional DPSM several point sources are placed near the transducer face, interface and anomaly boundaries. The ultrasonic or the electromagnetic field at any point is computed by superimposing the contributions of different layers of point sources strategically placed. The conventional DPSM modelling technique is modified in this paper so that the contributions of the point sources in the shadow region can be removed from the calculations. For this purpose the conventional point sources that radiate in all directions are replaced by Controlled Space Radiation (CSR) sources. CSR sources can take care of the shadow region problem to some extent. Complete removal of the shadow region problem can be achieved by introducing artificial interfaces. Numerically synthesized fields obtained by the conventional DPSM technique that does not give any special consideration to the point sources in the shadow region and the proposed modified technique that nullifies the contributions of the point sources in the shadow region are compared. One application of this research can be found in the improved modelling of the real time ultrasonic non-destructive evaluation experiments.
• Das, S., Dao, C. M., Banerjee, S., & Kundu, T. (2007). DPSM modeling for studying interaction between bounded ultrasonic beams and corrugated plates with experimental verification. IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, 54(9), 1860-1872.
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  PMID: 17941392;Abstract: Periodically corrugated structures play an important role in the field of vibration control and for designing structures with desired acoustic band gaps. Analytical solutions for corrugated plates are available for well-defined, smooth corrugations, such as sinusoidal corrugations that are not very common in the real world. Often corrugated plates are fabricated by cutting grooves at regular intervals in a flat plate. No analytical solution is available to predict the wave propagation behavior in such a periodically corrugated plate in which the equation of the plate surface changes periodically between a planar flat surface and a nonplanar parabolic groove. This problem is solved here for steady-state case by a newly developed semianalytical technique called distributed point source method (DPSM), and the theoretical predictions are compared with the experimental results generated by reflecting a bounded 2.25 MHz ultrasonic beam by a fabricated corrugated plate. The main difference that is observed in the reflected beam profile from a flat plate and a corrugated plate is that the back-scattering effect is much stronger for the corrugated plate, and the forward reflection is stronger for the flat plate. The energy distribution inside the corrugated plate also shows backward propagation of the ultrasonic energy. © 2007 IEEE.
• Das, S., Dao, C. M., Banerjee, S., & Kundu, T. (2007). DPSM modeling for studying interaction between bounded ultrasonic beams and corrugated plates with experimental verification. ieee transactions on ultrasonics, ferroelectrics, and frequency control, 54(9).
• Jata, K. V., Kundu, T., & Parthasarathy, T. A. (2007). An introduction to failure mechanisms and ultrasonic inspection. Advanced ultrasonic methods for material and structure inspection, 1--42.
• Kamanyi, A. E., Ngwa, W., Kundu, T., & Grill, W. (2007). Soft matter Acoustics: Non-destructive health monitoring of polymer blend films. Proceedings of SPIE - The International Society for Optical Engineering, 6531.
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  Abstract: Soft matter acoustics is concerned with the application of acoustical techniques in the study of soft matter. In this paper, we demonstrate the use of phase sensitive acoustic microscopy (PSAM) in synchronous mapping of three-dimensional heterogeneity of sample soft matter systems: thin film blends of polystyrene (PS) and poly (methylmethacrylate) (PMMA). The use of acoustic phase contrast imaging for cure or health monitoring of polymer systems is discussed.
• Kundu, T. (2007). Proceedings of SPIE - The International Society for Optical Engineering: Introduction. Proceedings of SPIE - The International Society for Optical Engineering, 6532, XV.
• Kundu, T., & Placko, D. (2007). Advanced Theory of DPSM—Modeling Multilayered Medium and Inclusions of Arbitrary Shape. DPSM for Modeling Engineering Problems, 59--96.
• Kundu, T., Ahmad, R., Alnuaimi, N., & Placko, D. (2007). Ultrasonic Modeling in Fluid Media. DPSM for Modeling Engineering Problems, 97--141.
• Kundu, T., Das, S., & Jata, K. V. (2007). An improved technique for locating the point of impact from the acoustic emission data. Proceedings of SPIE - The International Society for Optical Engineering, 6532.
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  Abstract: Triangulation technique for impact point location works very well when the acoustic emission sensors are placed at a relatively large distance from the point of impact. In this situation the time of arrival measurement is not affected significantly by the small error that might arise from not being able to pinpoint the exact time of arrival of the acoustic signal. The conventional technique also requires that the wave speed in the medium is well-known and non-dispersive in the frequency range of interest. If the receiving wave is a P-wave or S-wave or a non-dispersive Rayleigh wave then the conventional triangulation technique is reliable. In this paper it is shown that the conventional triangulation technique is not very reliable for locating the impact point in a plate when the sensors are placed close to the striking point for two reasons - first, it is difficult to pin point the exact time of arrival of the signal and secondly the Lamb modes in a plate are dispersive. Dispersive signals attenuate differently at various frequencies and propagate with different speeds causing distortions in the received signals and thus introduce more error in the time of flight measurement. In this paper an alternative approach is proposed to locate the impact point more accurately. Experiments are carried out with an aluminum plate. The impact points predicted by the conventional triangulation technique and the proposed modified method are compared.
• Kundu, T., Das, S., & Jata, K. V. (2007). Point of impact prediction in isotropic and anisotropic plates from the acoustic emission data. JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA, 122(4), 2057-2066.
• Kundu, T., Das, S., & Jata, K. V. (2007). Point of impact prediction in isotropic and anisotropic plates from the acoustic emission data. Journal of the Acoustical Society of America, 122(4), 2057-2066.
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  PMID: 17902843;Abstract: It is shown in this paper that the conventional triangulation technique is not very reliable for locating the impact point even in isotropic plates when the sensors are placed close to the point of strike for two reasons: First, it is difficult to pinpoint the exact time of arrival of the signal and, second, the Lamb modes in a plate are dispersive. Dispersive signals attenuate differently at various frequencies and propagate with different speeds causing distortions in the received signals, and thus introduce error in the time of flight measurement. The triangulation technique assumes that wave speeds in all directions are the same, which is not true for anisotropic plates. Here an alternative approach based on an optimization scheme is proposed to locate the point of impact in isotropic and anisotropic plates. A formulation is presented for the general anisotropic case. Experiments are carried out with an aluminum plate by dropping balls on the plate and picking up acoustic signals at different locations. The impact points predicted by the conventional triangulation technique and the proposed modified method are compared for this isotropic plate. Then it is investigated how the prediction would change if the plate is assumed to have some anisotropy. © 2007 Acoustical Society of America.
• Kundu, T., Das, S., Dao, C. M., Banerjee, S., & Kundu, T. -. (2007). DPSM modeling for studying interaction between bounded ultrasonic beams and corrugated plates with experimental verification. IEEE transactions on ultrasonics, ferroelectrics, and frequency control, 54(9).
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  Periodically corrugated structures play an important role in the field of vibration control and for designing structures with desired acoustic band gaps. Analytical solutions for corrugated plates are available for well-defined, smooth corrugations, such as sinusoidal corrugations that are not very common in the real world. Often corrugated plates are fabricated by cutting grooves at regular intervals in a flat plate. No analytical solution is available to predict the wave propagation behavior in such a periodically corrugated plate in which the equation of the plate surface changes periodically between a planar fiat surface and a nonplanar parabolic groove. This problem is solved here for steady-state case by a newly developed semianalytical technique called distributed point source method (DPSM), and the theoretical predictions are compared with the experimental results generated by reflecting a bounded 2.25 MHz ultrasonic beam by a fabricated corrugated plate. The main difference that is observed in the reflected beam profile from a flat plate and a corrugated plate is that the back-scattering effect is much stronger for the corrugated plate, and the forward reflection is stronger for the flat plate. The energy distribution inside the corrugated plate also shows backward propagation of the ultrasonic energy.
• Placko, D., & Kundu, T. (2007). Basic theory of Distributed Point Source Method (DPSM) and its application to some simple problems. DPSM for Modeling Engineering Problems, 1--58.
• Pradhan, B., Sinha, R. K., Singh, B. P., & Kundu, T. (2007). Origin of methyl torsional barrier in 1-methyl-2 (1H)-pyridinimine and 3-methyl-2 (1H)-pyridone: II. Ground state. The Journal of chemical physics, 126(11), 114313.
• Ahmad, R., Banerjee, S., & Kundu, T. (2006). Cylindrical guided waves for damage detection in underground pipes using wavelet transforms. Proceedings of SPIE - The International Society for Optical Engineering, 6174 II.
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  Abstract: This paper investigates if cylindrical guided waves can be effectively used for pipe wall defect detection in soil-embedded pipes. For this purpose guided waves are propagated through pipes that are buried in the soil by placing transmitters on one end of the pipes and the receivers on the other end. Received signals for both defect-free and defective pipes are subjected to wavelet transforms. It is found that when a Continuous Wavelet Transform (CWT) based algorithm is applied to analyze the received signals then it is very easy to make distinction between damaged and undamaged pipes. To investigate whether embedding the pipe in the soil makes it more difficult to detect the pipe wall defects, the same set of defective and defect-free pipes are analyzed before and after burying them in the soil. In both cases the defects are easily detected after analyzing the wavelet transformed signals. Interestingly it can be detected more easily for the buried pipes because the difference between the received signal strengths from defect-free and defective pipes is found to be greater for the buried pipes. For soil embedded pipes the ultrasonic energy scattered by the defect is absorbed by the surrounding soil making the energy reaching the receiver significantly weaker than that for the defect-free soil embedded pipe.
• Banerjee, S., & Kundu, T. (2006). Advanced Applications of Distributed Point Source Method - Ultrasonic Field Modeling in Solid Media. DPSM for Modeling Engineering Problems, 143-229.
• Banerjee, S., & Kundu, T. (2006). Elastic wave propagation in sinusoidally corrugated waveguides. JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA, 119(4), 2006-2017.
• Banerjee, S., & Kundu, T. (2006). Elastic wave propagation in sinusoidally corrugated waveguides. Journal of the Acoustical Society of America, 119(4), 2006-2017.
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  PMID: 16642814;Abstract: The ultrasonic wave propagation in sinusoidally corrugated waveguides is studied in this paper. Periodically corrugated waveguides are gaining popularity in the field of vibration control and for designing structures with desired acoustic band gaps. Currently only numerical method (Boundary Element Method or Finite Element Method) based packages (e.g., PZFlex) are in principle capable of modeling ultrasonic fields in complex structures with rapid change of curvatures at the interfaces and boundaries but no analyses have been reported. However, the packages are very CPU intensive; it requires a huge amount of computation memory and time for its execution. In this paper a new semi-analytical technique called Distributed Point Source Method (DPSM) is used to model the ultrasonic field in sinusoidally corrugated waveguides immersed in water where the interface curvature changes rapidly. DPSM results are compared with analytical solutions. It is found that when a narrow ultrasonic beam hits the corrugation peaks at an angle, the wave propagates in the backward direction in waveguides with high corrugation depth. However, in waveguides with small corrugation the wave propagates in the forward direction. The forward and backward propagation phenomenon is found to be independent of the signal frequency and depends on the degree of corrugation. © 2006 Acoustical Society of America.
• Banerjee, S., & Kundu, T. (2006). Scattering of ultrasonic waves by internal anomalies in plates immersed in a fluid. Proceedings of SPIE - The International Society for Optical Engineering, 6177.
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  Abstract: Non-Destructive Evaluation (NDE) of plate structures is frequently carried out in industrial and laboratory environments. In this paper the wave scattering from horizontally oriented internal cavities or cracks in a plate are studied using DPSM (Distributed Point Source Method). DPSM has gained popularity in last few years in the field of ultrasonic field modelling. DPSM is a semi-analytical technique that can be used to calculate the ultrasonic field (pressure, velocity and displacement fields in a fluid, or stress and displacement fields in a solid) generated by ultrasonic transducers. So far the technique has been used to model ultrasonic field near a fluid-solid interface when a solid half-space is immersed in a fluid. This method has also been used to model the ultrasonic field generated in a homogeneous isotropic solid plate immersed in a fluid. The objective of this study is to present the theoretical modelling of the diffraction and scattering pattern of guided waves in the solid plate when the transducers of finite dimension are placed on both side of the defective plate.
• Banerjee, S., & Kundu, T. (2006). Symmetric and anti-symmetric Rayleigh-Lamb modes in sinusoidally corrugated waveguides: An analytical approach. International Journal of Solids and Structures, 43(21), 6551-6567.
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  Abstract: The wave propagation analysis in corrugated waveguides is considered in this paper. Elastic wave propagation in a two-dimensional periodically corrugated plate is studied here analytically. The dispersion equation is obtained by applying the traction free boundary conditions. Solution of the dispersion equation gives both symmetric and anti-symmetric modes. In a periodically corrugated waveguide all possible spectral order of wave numbers are considered for the analytical solution. It has been observed that the truncation of the spectral order influences the results. Truncation number depends on the degree of corrugation and the frequency of the wave. Usually increasing frequency requires increasing number of terms in the series solution, or in other words, a higher truncation number. For different degrees of corrugation the Rayleigh-Lamb symmetric and anti-symmetric modes are investigated for their non-propagating 'stop bands' and propagating 'pass bands'. To generate the dispersion equation for corrugated plates with a wide range of the degree of corrugation, appropriate truncation of the spectral orders has to be considered. Analytical results are given for three different degrees of corrugation in three plates. Resonance of symmetric and anti-symmetric modes in these plates, their 'cut-off', 'cut-on', 'branch-point', 'change-place', 'mode conversion' and 'pinch points' at various frequencies are also studied. © 2006 Elsevier Ltd. All rights reserved.
• Banerjee, S., Kundu, T., & Placko, D. (2006). Ultrasonic field modeling in multilayered fluid structures using the distributed point source method technique. Journal of Applied Mechanics, Transactions ASME, 73(4), 598-609.
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  Abstract: In the field of nondestructive evaluation (NDE), the newly developed distributed point source method (DPSM) is gradually gaining popularity. DPSM is a semi-analytical technique used to calculate the ultrasonic field (pressure and velocity fields) generated by ultrasonic transducers. This technique is extended in this paper to model the ultrasonic field generated in multilayered nonhomogeneous fluid systems when the ultrasonic transducers are placed on both sides of the layered fluid structure. Two different cases have been analyzed. In the first case, three layers of nonhomogeneous fluids constitute the problem geometry; the higher density fluid is sandwiched between two identical fluid half-spaces. In the second case, four layers of nonhomogeneous fluids have been considered with the fluid density monotonically increasing from the bottom to the top layer. In both cases, analyses have been carried out for two different frequencies of excitation with various orientations of the transducers. As expected, the results show that the ultrasonic field is very sensitive to the fluid properties, the orientation of the fluid layers, and the frequency of excitation. The interaction effect between the transducers is also visible in the computed results. In the pictorial view of the resulting ultrasonic field, the interface between two fluid layers can easily be seen. Copyright © 2006 by ASME.
• Banerjee, S., Kundu, T., & Placko, D. (2006). Ultrasonic field modeling in multilayered fluid structures using the distributed point source method technique. Journal of applied mechanics, 73(4), 598--609.
• Jensen, A. S., Baandrup, U., Hasenkam, J. M., Kundu, T., & Jorgensen, C. S. (2006). Distribution of the microelastic properties within the human anterior mitral leaflet. Ultrasound in medicine & biology, 32(12), 1943--1948.
• Jensen, A. S., Baandrup, U., Hasenkam, J. M., Kundu, T., & Jørgensen, C. S. (2006). Distribution of the microelastic properties within the human anterior mitral leaflet. Ultrasound in Medicine and Biology, 32(12), 1943-1948.
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  PMID: 17169706;Abstract: Knowledge of the biomechanical properties of the mitral valve leaflets and their relation to histologic structure is of importance for understanding the leaflet movement characteristics under normal and pathologic conditions, but such knowledge is not yet available. The aim of this study was to determine biomechanical properties of the human anterior mitral leaflet on a microscopic scale. We used scanning acoustic microscopy (SAM) to examine the human anterior mitral leaflet. Sections of fixed human anterior mitral leaflet tissue were obtained from postmortem human anterior mitral leaflets (n = 5). We measured the speed of sound (νL) in each histologic layer in three regions-of-interest (ROIs): these were at the annular edge, at the valve midpoint and close to the free edge. νL varied in the three histologic layers (p < 0.01). It was higher in the fibrous layer (1.76 km/s) compared with the atrial layer (1.75 km/s) and ventricular layer (1.73 km/s). Also, νL differed between positions along the length of the annulus-free edge line (p < 0.01), showing a decline from the annular edge (1.76 km/s) to the free edge (1.73 km/s), both as a whole and also within the atrial and the fibrous layer. These results demonstrate that the fibrous layer is stiffer than the atrial and ventricular layer and that the leaflet as a whole and within the atrial and the fibrous layer is stiffer at the annulus part in comparison with those near the free edge. (E-mail: asj@ki.au.dk). © 2006 World Federation for Ultrasound in Medicine & Biology.
• Kundu, T. (2006). Proceeding of SPIE - The International Society for Optical Engineering: Introduction. Proceedings of SPIE - The International Society for Optical Engineering, 6177, xiii.
• Kundu, T., & Placko, D. (2006). Advanced Theory of DPSM-Modeling Multilayered Medium and Inclusions of Arbitrary Shape. DPSM for Modeling Engineering Problems, 59-96.
• Kundu, T., Ahmad, R., Alnuaimi, N., & Placko, D. (2006). Ultrasonic Modeling in Fluid Media. DPSM for Modeling Engineering Problems, 97-141.
• Kundu, T., Banerjee, S., & Jata, K. V. (2006). An experimental investigation of guided wave propagation in corrugated plates showing stop bands and pass bands. JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA, 120(3), 1217-1226.
• Kundu, T., Banerjee, S., & Jata, K. V. (2006). An experimental investigation of guided wave propagation in corrugated plates showing stop bands and pass bands. Journal of the Acoustical Society of America, 120(3), 1217-1226.
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  Abstract: Nonplanar surfaces are often encountered in engineering structures. In aerospace structures, periodically corrugated boundaries are formed by friction-stir-welding. In civil engineering structures, rebars used in reinforced concrete beams and slabs have periodic surface. Periodic structures are also being used to create desired acoustic band gaps. For health monitoring of these structures, a good understanding of the elastic wave propagation through such periodic structures is necessary. Although a number of research papers on the wave propagation in periodic structures are available in the literature, no one experimentally investigated the guided wave propagation through plates with periodic boundaries and compared the experimental results with theoretical predictions as done in this paper. The experimental results clearly show that elastic waves can propagate through the corrugated plate (waveguide) for certain frequencies called "pass bands," and find it difficult to propagate for some other frequencies called "stop bands." Stop bands are found to increase with the degree of corrugation. Experimental results are compared with the theoretical predictions, and good matching is observed for plates with small degree of corrugation. Only two parameters - the depth of corrugation and the wavelength of the periodicity-are sufficient for modeling the elastic wave propagation in slightly corrugated plates. © 2006 Acoustical Society of America.
• Kundu, T., Banerjee, S., & Jata, K. V. (2006). An experimental investigation of guided wave propagation in corrugated plates. Proceedings of the 3rd European Workshop - Structural Health Monitoring 2006, 1037-1044.
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  Abstract: Non-planar surfaces are often encountered in engineering structures. Periodically corrugated boundaries can be found in aerospace structural components such as the surface formed by friction stir welding, and in civil structural components such as rebars used inside reinforced concrete beams and slabs. Engineers and architects also design periodically corrugated structures to create desired acoustic band gaps. For health monitoring of structures with periodic geometry a good understanding of the elastic wave propagation phenomenon through such periodic structures is necessary because crack initiation creates acoustic waves that propagate through the periodic geometry of the structure. These acoustic signals can be detected at remote locations and correctly interpreted only if the mechanics of elastic wave propagation through such periodic structures is well understood. With this application in mind the elastic wave propagation in three different plates with different degrees of corrugation is experimentally studied. The experimental results clearly show that elastic waves can propagate through the corrugated plate (waveguide) for certain frequencies and find it difficult to propagate for some other frequencies. Frequencies that allow the elastic waves to propagate through the plate are called pass band frequencies while the frequencies that block the wave propagation are called stop band frequencies. Pass band and stop band frequencies depend on the geometry of the corrugated plate as well as the phase velocity of the propagating guided wave. Stop bands increase with the degree of corrugation. Experimental results are compared with the theoretical predictions.
• Kundu, T., Banerjee, S., & Kundu, T. -. (2006). Elastic wave propagation in sinusoidally corrugated waveguides. The Journal of the Acoustical Society of America, 119(4).
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  The ultrasonic wave propagation in sinusoidally corrugated waveguides is studied in this paper. Periodically corrugated waveguides are gaining popularity in the field of vibration control and for designing structures with desired acoustic band gaps. Currently only numerical method (Boundary Element Method or Finite Element Method) based packages (e.g., PZFlex) are in principle capable of modeling ultrasonic fields in complex structures with rapid change of curvatures at the interfaces and boundaries but no analyses have been reported. However, the packages are very CPU intensive; it requires a huge amount of computation memory and time for its execution. In this paper a new semi-analytical technique called Distributed Point Source Method (DPSM) is used to model the ultrasonic field in sinusoidally corrugated waveguides immersed in water where the interface curvature changes rapidly. DPSM results are compared with analytical solutions. It is found that when a narrow ultrasonic beam hits the corrugation peaks at an angle, the wave propagates in the backward direction in waveguides with high corrugation depth. However, in waveguides with small corrugation the wave propagates in the forward direction. The forward and backward propagation phenomenon is found to be independent of the signal frequency and depends on the degree of corrugation.
• Kundu, T., Lee, J., Blase, C., & Bereiter-Hahn, J. (2006). Acoustic microscope lens modeling and its application in determining biological cell properties from single- and multi-layered cell models. Journal of the Acoustical Society of America, 120(3), 1646-1654.
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  PMID: 17004486;Abstract: The acoustic microscopy technique provides some extraordinary advantages for determining mechanical properties of living cells. It is relatively fast, of excellent spatial resolution, and of minimal invasiveness. Sound velocity is a measure of the cell stiffness. Attenuation of cytoplasm is a measure of supramolecular interactions. These parameters are of crucial interest for studying cell motility and volume regulations and to establish the functional role of the various elements of the cytoskeleton. Using a scanning acoustic microscope, longitudinal wave speed, attenuation and thickness profile of a biological cell were measured earlier by Kundu et al. [Biophys. J. 78, 2270-2279 (2000)]. In that study it was assumed that the cell properties did not change through the cell thickness but could vary in the lateral direction. In that effort the acoustic-microscope-generated signal was modeled as a plane wave striking the cell at normal incidence. Such assumptions ignored the effect of cell inhomogenity and the surface skimming Rayleigh waves. In this paper a rigorous lens model, based on the DPSM (distributed point source method), is adopted. For the first time in the literature the cell is modeled here as a multi-layered material and the effect of some external drug stimuli on a living cell is studied. © 2006 Acoustical Society of America.
• Kundu, T., Lee, J., Blase, C., & Bereiter-Hahn, J. (2006). Acoustic microscope lens modeling and its application in determining biological cell properties from single-and multi-layered cell models. The Journal of the Acoustical Society of America, 120(3), 1646--1654.
• Kundu, T., Reibel, R., & Jata, K. V. (2006). Fundamental ultrasonic wave propagation studies in a model thermal protection system (porous tiles bonded to aluminum bulkhead). Proceedings of SPIE - The International Society for Optical Engineering, 6177.
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  Abstract: A model thermal protection system (TPS) was designed by bonding ceramic porous tiles to 2.2 and 3.5 mm thick 2124-T351 aluminum alloy plates. One of the goals of the present work was to investigate the potential of detecting simulated defects using guided waves. Simulated defects consisted of cracks, voids and delaminations at the tile-substrate interface. Cracks and voids were introduced into the porous tiles during the fabrication of the TPS. Delamination was created by cutting the gluing tape between the tile and the aluminum substrate. Guided wave propagation studies were conducted using the pitch-catch approach, while changing the angle of strike and the frequency of the transducer excitation to generate the appropriate guided wave mode. The receiver was placed at a distance so that only the guided waves were received during the immersion experiment. The delamination defect could be conclusively detected, however the presence of the imperfect bond between the tiles and the substrate interfered with the detection of the simulated cracks and voids in the porous tiles.
• Placko, D., & Kundu, T. (2006). Basic Theory of Distributed Point Source Method (DPSM) and Its Application to Some Simple Problems. DPSM for Modeling Engineering Problems, 1-58.
• Placko, D., & Kundu, T. (2006). DPSM for Modeling Engineering Problems. DPSM for Modeling Engineering Problems, 1-372.
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  Abstract: This book is the first book on this technique; it describes the theory of DPSM in detail and covers its applications in ultrasonic, magnetic, electrostatic and electromagnetic problems in engineering. For the convenience of the users, the detailed theory of DPSM and its applications in different engineering fields are published here in one book making it easy to acquire a unified knowledge on DPSM.© 2007 John Wiley & Sons, Inc..
• Placko, D., & Kundu, T. (2006). Preface. DPSM for Modeling Engineering Problems, xv.
• Ahmad, R., Banerjee, S., & Kundu, T. (2005). Influence of water flow on pipe inspection. Proceedings of SPIE - The International Society for Optical Engineering, 5768, 285-294.
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  Abstract: From various studies by different investigators it has been now well established that a number of cylindrical guided wave modes are sensitive to the pipe wall defects. Several investigations by these authors and other researchers showed that the strengths of the guided waves propagating through a pipe that is placed in air are reduced when the pipe wall defects are encountered. This reduction is expected because the pipe wall defects (gouge, dent, removed metal due to corrosion etc.) alter the pipe geometry, hampering the free propagation of guided wave modes. When water flows through the pipes, the guided wave technique becomes more challenging because the flowing water absorbs part of the propagating acoustic energy. Flowing water may also induce some standing modes. The propagating cylindrical guided wave modes become leaky modes in presence of the flowing water, in other words energy leaks into water. Therefore, the energy detected by a receiver, placed at a large distance from the transmitter, is reduced even for a defect free pipe. Further reduction in the signal strength occurs in presence of defects.
• Ahmad, R., Kundu, T., & Placko, D. (2005). Modeling of phased array transducers. JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA, 117(4), 1762-1776.
• Ahmad, R., Kundu, T., & Placko, D. (2005). Modeling of phased array transducers. Journal of the Acoustical Society of America, 117(4 I), 1762-1776.
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  PMID: 15898623;Abstract: Phased array transducers are multi-element transducers, where different elements are activated with different time delays. The advantage of these transducers is that no mechanical movement of the transducer is needed to scan an object. Focusing and beam steering is obtained simply by adjusting the time delay. In this paper the DPSM (distributed point source method) is used to model the ultrasonic field generated by a phased array transducer and to study the interaction effect when two phased array transducers are placed in a homogeneous fluid. Earlier investigations modeled the acoustic field for conventional transducers where all transducer points are excited simultaneously. In this research, combining the concepts of delayed firing and the DPSM, the phased array transducers are modeled semi-analytically. In addition to the single transducer modeling the ultrasonic fields from two phased array transducers placed face to face in a fluid medium is also modeled to study the interaction effect. The importance of considering the interaction effect in multiple transducer modeling is discussed, pointing out that neighboring transducers not only act as ultrasonic wave generators but also as scatterers. © 2005 Acoustical Society of America.
• Ahmad, R., Kundu, T., & Placko, D. (2005). Modeling of phased array transducers. The Journal of the Acoustical Society of America, 117(4), 1762--1776.
• Banerjee, S., & Kundu, T. (2005). Elastic wave propagation in corrugated plates. Proceedings of SPIE - The International Society for Optical Engineering, 5768, 323-333.
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  Abstract: Analysis of Wave propagation in plates with sinusoidal boundaries has been considered in this paper. Guided elastic wave in a two-dimensional periodically corrugated plate is studied analytically. The plate material is considered as homogeneous, isotropic and linearly elastic. In a periodically corrugated wave-guide all possible spectral order of wave numbers are considered. The dispersion equation is obtained by applying the traction free boundary conditions. Solution of the dispersion equation includes both symmetric and anti-symmetric mode. Non-propagating 'stop bands' and propagating 'pass bands' are investigated.
• Dube, M., & Kundu, T. (2005). Yield function for solder elastoviscoplastic modeling. Journal of Electronic Packaging, Transactions of the ASME, 127(2), 147-156.
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  Abstract: Field reliability extrapolations from accelerated tests necessitate simulation of a variety of material behaviors under general loading conditions. The Hierarchical Incremental Single Surface (HiSS) yield function (Desai, C. S., 200I, Mechanics of Materials and Interfaces: The Disturbed State Concept, CRC Press, Boca Raton, FL.) has been applied extensively to a wide range of materials, from solders and silicon to ceramics and geotechnical materials, for simulating continuous-yield elastoplastic and elastoviscoplastic behavior. This work presents a continuous-yield function that avoids problems with HiSS for thermal and tensile loading. Validations are presented for eutectic Pb/Sn data of Wang et al. (Wang, Z., Desai, C.S., and Kundu, T., 2001, "Disturbed State Constitutive Modeling and Testing of Joining Materials in Electronic Packaging," report to NSF for Materials Processing and Manufacturing Division Grant 9812686, University of Arizona, Tucson, AZ). Limitations on the range of validity of the elastoplastic and the Perzyna elastoviscoplastic formulations are discussed. Copyright © 2005 by ASME.
• Dube, M., & Kundu, T. (2005). Yield function for solder elastoviscoplastic modeling. Journal of Electronic Packaging, 127(2), 147--156.
• Kundu, T. (2005). NONLINEAR OPTICAL MATERIALS 1. Introduction Nonlinear optical (NLO) materials are the building blocks of the emerging tech-nologies of optoelectronics and photonics (the acquisition, transmission, proces. Kirk-Othmer encyclopedia of chemical technology, 17, 442.
• Kundu, T. (2005). Proceedings of SPIE - The International Society for Optical Engineering: Introduction. Proceedings of SPIE - The International Society for Optical Engineering, 5768, xi.
• Kundu, T., Blase, C., & Bereiter-Hahn, J. (2005). Determination of cell properties from single and multi-layered cell models. Proceedings of SPIE - The International Society for Optical Engineering, 5768, 44-54.
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  Abstract: Among the methods for the determination of mechanical properties of living cells acoustic microscopy provides some extraordinary advantages. It is relatively fast, of excellent spatial resolution and of minimal invasiveness. Sound velocity is a measure of the stiffness of the cell. Attenuation of cytoplasm is a measure of supramolecular interactions. These parameters are of crucial interest for studies of cell motility, volume regulations and to establish the functional role of the various elements of the cytoskeleton. Using a phase and amplitude sensitive scanning acoustic microscope, longitudinal wave speed, attenuation and thickness profile of a biological cell have been measured earlier by Kundu, Bereiter-Hahn and Karl1 (2000) from the voltage versus frequency or V(f) curves in the frequency range 980-1100 MHz. Two limitations of that study are overcome in this paper. In that study it was assumed that the cell properties did not change through the cell thickness and could vary only in the lateral direction. Secondly, the acoustic microscope generated ultrasonic signal was modeled in that study as a plane wave striking the cell and the substrate at normal incidence. Such assumption ignores the contribution of the surface skimming Rayleigh waves. Improved and more generalized analysis that is presented here avoids such restrictive assumptions. For the first time, in this paper the cell is modeled as a multi-layered material with different properties for nucleus and surrounding cell material. The inverse problem is solved to study the effect of drugs on living cells.
• Na, W., Kundu, T., Ryu, Y., & Kim, J. (2005). Concrete filled steel pipe inspection using electro magnetic acoustic transducer (EMAT). Proceedings of SPIE - The International Society for Optical Engineering, 5765(PART 1), 74-84.
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  Abstract: Concrete-filled steel pipes are usually exposed in hostile environments such as seawater and deicing materials. The outside corrosion of the steel pipe can reduce the wall thickness and the corrosion-induced delamination of internal concrete can increase internal volume or pressure. In addition, the void that can possibly exist in the pipe reduces the bending resistance. To avoid structural failure due to this type of deterioration, appropriate inspection and repair techniques are to be developed. Guided wave techniques have strong potentials for this kind of inspection because of long-distance inspection capability. Among different transducer-coupling mechanism, electro-magnetic acoustic transducers (EMATs) give relatively consistent results in comparison to piezoelectric transducers since they do not need any couplant. In this study EMATs are used for transmitting and receiving cylindrical guided waves through concrete-filled steel pipes. Through time history curves and wavelet transform, it is shown that EMAT-generated cylindrical guided wave techniques have good potential for the interface inspection of concrete-filled steel pipes.
• Ngwa, W., Luo, W., Kundu, T., & Grill, W. (2005). Acoustic phase micrographs in mesoscale materials characterization. Proceedings of SPIE - The International Society for Optical Engineering, 5768, 27-35.
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  Abstract: Acoustic techniques are widely employed in health monitoring and nondestructive evaluation of materials. Phase micrographs obtained by phase-sensitive acoustic techniques often contain useful information complementary to the information acquirable from amplitude micrographs alone. Most of this information remains relatively unexploited due to the difficulties encountered in unwrapping and processing of the raw phase data. In this work, a review of the derivable information from the phase images of a scanning acoustic microscope with phase contrast (PSAM) is presented. Different perspectives and insights on sample structural and biological mesocale systems are discussed, predicated on phase information obtained by simulations and three-dimensional imaging.
• Banerjee, S., & Kundu, T. (2004). Elastic wave propagation in symmetrically periodic sinusoidal waveguide. Proceedings of SPIE - The International Society for Optical Engineering, 5394, 89-98.
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  Abstract: Wave propagation in structures with irregular boundaries is studied by transforming the plates with irregular surfaces to sinusoidal wave-guides. Guided elastic wave in a two-dimensional periodically corrugated plate is studied analytically. The plate material is considered as homogeneous, isotropic and linearly elastic. In a periodically corrugated wave-guide all possible spectral order of wave numbers are considered. The dispersion equation is obtained by applying the traction free boundary conditions. The analysis is carried out in the wave-number domain for symmetric modes. Non-propagating 'stop bands' and propagating 'pass bands' are investigated.
• Desai, C. S., Wang, Z., Whitenack, R., & Kundu, T. (2004). Testing and modeling of solders using new test device, part 1: Models and testing. Journal of Electronic Packaging, Transactions of the ASME, 126(2), 225-231.
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  Abstract: The development and use of a new testing device called the thermomechanical-digital image correlation (TM-DIC), for testing and modeling of solders, was discussed. The TM-DIC device is capable of multidimensional (shear and normal) loading, temperature control (isothermal and thermomechanical), different rates of loading and creep at constant stress or displacement. The DIC provides advantages such as use of very small specimens and avoidance of grid attachment. The DIC is less robust than the foregoing methods and provides very good measurements to monitor strain, microcracking and fracture. The DIC software developed by K&T Measuring System, Germany has been integrated in TM-DIC.
• Desai, C. S., Wang, Z., Whitenack, R., & Kundu, T. (2004). Testing and modeling of solders using new test device, part 2: Calibration and validation. Journal of Electronic Packaging, 126(2), 232--236.
• Dosai, C. S., Wang, Z., Whitenack, R., & Kundu, T. (2004). Testing and modeling of solders using new test device, part 2: Calibration and validation. Journal of Electronic Packaging, Transactions of the ASME, 126(2), 232-236.
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  Abstract: The determination of disturbed state concept (DSC) parameters by following different procedures was presented. It was found that some of the parameters were not significantly influenced by temperature and strain rates. The DSC model was used to predict typical stress-strain data and for a boundary value problem involving a thin small outline package (TSOP). The DCS model can provide a unified approach toward modeling the behavior including elastic, plastic and creep strains, and microcracking leading to fracture, softening and failure.
• Kundu, T. (2004). Nondestructive Evaluation. Kirk-Othmer Encyclopedia of Chemical Technology.
• Ngwa, W., Grill, W., & Kundu, T. (2004). Bio-soft matter imaging and micro-metrology by Phase-sensitive ultrasonic microscopy. Proceedings of SPIE - The International Society for Optical Engineering, 5394, 263-272.
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  Abstract: Phase-sensitive acoustic microscopy (PSAM) is used for investigating bio-soft matter systems constituting the important biopolymer and biomaterial chitosan. Incipient micro-analytic ways for the determination of mechanical properties from the simultaneously obtained amplitude and phase images, allow the coeval estimation of the depth of structures and acoustic velocities, from which the density, stiffness and other elastic parameters may be derived. Chitosan is an important derivative from chitin the major component of the carapace (also examined here) of living species like Daphnia. The results obtained exemplify the unique power of PSAM for revealing essential features and information in biological soft matter.
• Ngwa, W., Wannemacher, R., Grill, W., Serghei, A., Kremer, F., & Kundu, T. (2004). Voronoi Tessellations in Thin Polymer Blend Films. Macromolecules, 37(5), 1691-1692.
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  Abstract: An unusual polymer blend morphology of Voronoi Tessellations is discussed. AFM and phase-sensitive acoustic microscopy (PSAM) techniques are used for the purpose. Findings suggest that the congenitally entropy-driven phase separation process for polymer blend films may follow a quasi-Voronoi tessellation generation mechanism or engender a Voronoi tessellation stage. This propounds a newfangled way for modeling the phase-separation process during spin-coating.
• Ngwa, W., Wannemacher, R., Grill, W., Serghei, A., Kremer, F., & Kundu, T. (2004). Voronoi tessellations in thin polymer blend films. Macromolecules, 37(5), 1691--1692.
• Kundu, T. (2003). Mechanics of elastic waves and ultrasonic nondestructive evaluation. Ultrasonic Nondestructive Evaluation: Engineering and Biological Material Characterization (CRC press, New York, 2003), 1--95.
• Kundu, T. (2003). Proceedings of SPIE - The International Society for Optical Engineering: Introduction. Proceedings of SPIE - The International Society for Optical Engineering, 5047, xi.
• Na, W. B., Kundu, T., & Ehsani, M. R. (2003). Lamb waves for detecting delamination between steel bars and concrete. COMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, 18(1), 58-63.
• Na, W., & Kundu, T. (2003). Inspection of interfaces between corroded steel bars and concrete using the combination of a piezoelectric zirconate-titanate transducer and an electromagnetic acoustic transducer. Experimental mechanics, 43(1), 24--31.
• Na, W., Kundu, T., & Ehsani, M. R. (2003). A comparison of steel/concrete and glass fiber reinforced polymers/concrete interface testing by guided waves. Materials Evaluation, 61(2), 155-161.
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  Abstract: Glass fiber reinforced polymer rods or bars are being used for reinforcing concrete structures. In comparison to conventional steel reinforcing bars, the glass fiber reinforced polymer bars are less likely to corrode when subjected to deicing materials and seawater. However, glass fiber reinforced polymers can be corroded due to chemical reactions that are different from the ones that corrode steel. This corrosion can deteriorate the glass fiber reinforced polymer/concrete interface and cause delamination or loss of bond, the most common secondary interface deterioration in reinforced concrete. Ultrasonic guided waves, because of their long distance testing capability, have been used for detecting delamination at the steel/concrete interface. In this paper, the possibility of developing similar guided wave testing techniques for testing glass fiber reinforced polymer/concrete interface delamination is investigated. Developing ultrasonic techniques for glass fiber reinforced polymer/concrete interface testing is more challenging because glass fiber reinforced polymers have high attenuation. Hence, many techniques that are used for steel testing do not work very well for fiber reinforced polymers. Here the ultrasonic guided wave technique is applied to concrete beams reinforced by glass fiber reinforced polymer bars to investigate the effect of high attenuation. This study shows that the ultrasonic guided wave testing technique has potential for both glass fiber reinforced polymer/concrete and steel/concrete interface testing.
• Na, W., Kundu, T., & Ehsani, M. R. (2003). Lamb waves for detecting delamination between steel bars and concrete. Computer-Aided Civil and Infrastructure Engineering, 18(1), 58-63.
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  Abstract: The feasibility of detecting interface degradation and separation of steel bars in concrete beams using Lamb waves is investigated in this paper. The Lamb wave can propagate a long distance along the reinforcing steel bars embedded in concrete as the guided wave and is sensitive to the interface bonding condition between the steel bar and the concrete. The traditional ultrasonic methods for inspecting defects in concrete use reflection, transmission, and scattering of longitudinal waves by internal defects. These methods are good for detecting large voids in concrete, but they are not very efficient for detecting delamination at the interface between concrete and steel bars. In this study, a special coupler between the steel bar and ultrasonic transducers has been used to launch nonaxisymmetric guided waves in the steel bar. This investigation shows that the Lamb wave inspection technique is an efficient and effective tool for health monitoring of reinforced concrete structures.
• Ngwa, W., Wannemacher, R., Grill, W., & Kundu, T. (2003). Phase-sensitive acoustic imaging and micro-metrology of polymer blend thin films. EPL (Europhysics Letters), 64(6), 830.
• Ngwa, W., Wannemacher, R., Grill, W., & Kundu, T. (2003). Phase-sensitive acoustic imaging and micro-metrology of polymer blend thin films. Europhysics Letters, 64(6), 830-836.
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  Abstract: Scanning acoustic microscopy with vector contrast (PSAM) at 1.2 GHz is employed for three-dimensional real-space measurements of structure in PS/PMMA (polystyrene/ poly(methyl methacrylate)) blend films, spun-cast on glass and silicon substrates. Processing of the digitized phase and amplitude images yields information on the surface structure and internal structure of the blend films. The complex V(z) functions render qualitative and quantitative material contrast for each image pixel and, hence, permit the characterization of individual domains. It is shown that PSAM can provide valuable insights regarding the polymer blend film morphology and micro-mechanical properties, not acquirable by other ways.
• Placko, D., Kundu, T., & Ahmad, R. (2003). Ultrasonic Field Computation in Presence of a Scatterer of Finite Dimension. Proceedings of SPIE - The International Society for Optical Engineering, 5047, 169-179.
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  Abstract: A recently developed semi-analytical technique called DPSM (Distributed Point Source Method) is improved and used to model the ultrasonic field in a fluid generated by an ultrasonic transducer and scattered by a solid plate of finite dimension. Earlier works on the ultrasonic field modeling by the DPSM technique have been limited to homogeneous fluids or non-homogeneous media with infinite interfaces. This is the first attempt to model the complete ultrasonic field consisting of incident, reflected, transmitted and diffracted fields by a finite scatterer of any shape or size. No closed form analytical solution exists for ultrasonic field computation in presence of a scatterer and an ultrasonic transducer, both of which can have finite dimensions and any shape. Finite element solution for wave propagation analysis is very time consuming; therefore, the semi analytical technique used here appears to be the method of choice for solving such practical problems. The paper shows how the scattered field varies as the striking angle and dimensions of the scatterer change.
• Towfighi, S., & Kundu, T. (2003). Elastic wave propagation in anisotropic spherical curved plates. International Journal of Solids and Structures, 40(20), 5495-5510.
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  Abstract: Spherical plate-like structures are used in pressure vessels, spherical domes of power plants, and in many other industrial applications. For non-destructive evaluation of such spherical structures, the mechanics of elastic wave propagation in spherical curved plates must be understood. The current literature shows some valuable studies on Rayleigh surface wave propagation in isotropic solids with spherical boundaries. However, the guided wave propagation problem in an anisotropic spherical curved plate, which has not been studied before, is solved for the first time in this paper. The wave propagation, in both isotropic and anisotropic spherical curved plates, is investigated. The differential equations of motion and the stress-free boundary conditions on the inner and outer surfaces of a hollow sphere are approximately solved by a general solution technique. This solution technique was successfully utilized by the authors for solving the wave propagation problem in cylindrical plates, in their earlier works. Dispersion curves for spherical plates made of isotropic aluminum, steel, and anisotropic composite material are presented as well. © 2003 Elsevier Ltd. All rights reserved.
• Desai, C. S., Kundu, T., & Lei, X. (2002). Introductory Finite Element Method. Applied Mechanics Reviews, 55, B2.
• Jorgensen, C. S., & Kundu, T. (2002). Measurement of material elastic constants of trabecular bone: a micromechanical analytic study using a 1 GHz acoustic microscope. Journal of Orthopaedic Research, 20(1), 151--158.
• Jung, Y., Kundu, T., & Ehsani, M. R. (2002). A new nondestructive inspection technique for reinforced concrete beams. ACI Materials Journal, 99(3), 292-299.
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  Abstract: This paper investigated the feasibility of detecting internal defects (cracks, honeycombs, and inclusions) in reinforced concrete (RC) beams using ultrasonic guided waves. Experiments were carried out on full-scale beams. It is shown that for RC beam inspections, the guided wave technique was better than the conventional stress wave techniques. The difference between the ultrasonic signals from the good and defective regions of the concrete beam was found to be much greater for the guided wave technique in comparison to the through-transmission or reflection mode ultrasonic techniques carried out in the same frequency range. Another advantage of the guided wave technique is that the guided waves have multiple modes of propagation. This paper also discusses how to generate the most efficient guided wave mode by adjusting signal frequency and angle of incidence.
• Jung, Y., Kundu, T., & Ehsani, M. R. (2002). A new nondestructive inspection technique for reinforced concrete beams. ARIEL, 129, 31--248.
• Jørgensen, C., & Kundu, T. (2002). Measurement of material elastic constants of trabecular bone: A micromechanical analytic study using a 1 GHz acoustic microscope. Journal of Orthopaedic Research, 20(1), 151-158.
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  PMID: 11853082;Abstract: The propagation speed (C) of surface acoustic waves (SAW), e.g. Rayleigh (R-waves) and longitudinal lateral waves (L-waves), the latter being the surface manifestation of the longitudinal waves, strongly reflect mechanical properties of materials. In view of an increasing interest in ultrasonic methodology in the field of bone biomechanics, we tested the hypothesis that both R- and L-waves can be excited in trabecular bone using an acoustic microscope at 1 GHz and that their speeds (CR and CL) can be extracted from V(z)-curves, i.e. plots of lens output voltage as a function of the lens focal point position with respect to the specimen surface. In accordance with V(z)-curves theoretically synthesized on the basis of incident field theory, experimental curves for canine femoral trabecular bone showed evidence of both R- and L-waves in almost all regions of recording. The measured CR ranged between 1.93 and 2.07 km/s (mean ± SD.: 2.00 ± 0.06 km/s) and the CL ranged between 2.33 and 4.33 km/s (3.37 ± 0.61 km/s). Knowledge of both speeds allowed computation of a number of material constants by means of simple theory of elasticity and assumptions of the material density. We found values of Poisson ratio (v) ranging from 0.14 to 0.32 (0.23 ± 0.07), Young's modulus (E) from 15 to 22.8 GPa (19.9 ± 2.5 GPa) and the shear modulus (G) from 7.6 to 8.9 GPa (8.4 ± 0.5 GPa). Anisotropy in the trabecular bone material was clearly detected at the micrometer level. In conclusion, the V(z)-curve method was successfully used to determine the distribution of material elastic constants of trabecular bone with micrometer resolution. © 2002 Orthopaedic Research Society. Published by Elsevier Science Ltd. All rights reserved.
• Kundu, T. (2002). Erratum: (Smart Non Destructive Evaluation for Health Monitoring of Structural and Biological Systems (18-19 March 2002)). Proceedings of SPIE - The International Society for Optical Engineering, 4702, 466-.
• Kundu, T. (2002). Proceedings of SPIE - The International Society for Optical Engineering: Introduction. Proceedings of SPIE - The International Society for Optical Engineering, 4702, xi.
• Kundu, T., & Jorgensen, C. S. (2002). Measuring elastic properties of bones and silicon from V (z) curve generated by multiply reflected signals. Ultrasonics, 39(7), 515--524.
• Kundu, T., & Jørgensen, C. (2002). Measuring elastic properties of bones and silicon from V(z) curve generated by multiply reflected signals. Ultrasonics, 39(7), 515-524.
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  PMID: 12102395;Abstract: Acoustic microscopes can be used to measure Rayleigh and longitudinal or P-wave speeds in a specimen at microscopic resolution. The wave speeds are obtained from the interference pattern as a function of the defocus distance or V(z) curve. The received signal voltage amplitude V is generated by two beams - the normally reflected central beam and a non-specularly reflected beam that strikes the fluid-solid interface at critical angle. It is shown in this paper that instead of analyzing the interference pattern between these two beams if we consider two other beams that follow the same path but travel through the coupling fluid multiple times before interfering then the V(z) curve generated by this higher order interference gives more accurate values for the material properties. The spacing distance between two successive dips of the V(z) curve is smaller for the higher order interference. The higher order interference, although weaker, gives more accurate results. Justification for the greater accuracy of the higher order interference is given in the paper. Material properties of silicon and bone are obtained by the new technique. Bones are microscopically heterogeneous and anisotropic. Anisotropic properties of homogeneous specimens can be obtained by the line focus acoustic microscope; however, it does not work when the specimen is microscopically heterogeneous. An attempt has been made here to obtain anisotropic properties of bones using point focus lens. © 2002 Elsevier Science B.V. All rights reserved.
• Miller, T., Hauser, C. J., & Kundu, T. (2002). Nondestructive inspection of corrosion and delamination at the concrete-steel reinforcement interface. ASME International Mechanical Engineering Congress and Exposition, Proceedings, 121-128.
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  Abstract: This paper explores the feasibility of detecting and quantifying corrosion and delamination at the interface between reinforcing steel bar and concrete using ultrasonic guided waves. The problem of corrosion and delamination of the reinforcing steel in the aging infrastructure has increased significantly in the last three decades and is likely to keep on increasing. Ultrasonic cylindrical guided waves that can propagate a long distance along the reinforcing steel bar are found to be sensitive to the interface conditions between steel bar and concrete. Ultrasonic transducers are used to launch and detect cylindrical guided waves along the steel bar. The traditional ultrasonic testing methods, for instance the pulse-echo method, where reflection, transmission, and scattering of longitudinal waves are used for detecting large voids in concrete, are not very efficient for detecting corrosion and delamination at the interface between concrete and steel bar. For this study four sets of specimens were prepared. They are rebars and plain steel bars with corrosion and physical separation. Transducers used during the experiment are the Electromagnetic Acoustic Transducer (EMAT) and the Piezoelectric Transducer (PZT). The experiment suggests that the guided wave inspection technique is feasible for the health monitoring of reinforced concrete structures. It also reveals that the ultrasonic guided waves are sensitive to the type of steel used and to the rib patterns on the reformed steel bars. Copyright © 2002 by ASME.
• Miller, T., Hauser, C. J., & Kundu, T. (2002). Nondestructive inspection of corrosion and delamination at the concrete-steel reinforcement interface. American Society of Mechanical Engineers (Publication) NDE, 23, 121-128.
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  Abstract: This paper explores the feasibility of detecting and quantifying corrosion and delamination at the interface between reinforcing steel bar and concrete using ultrasonic guided waves. The problem of corrosion and delamination of the reinforcing steel in the aging infrastructure has increased significantly in the last three decades and is likely to keep on increasing. Ultrasonic cylindrical guided waves that can propagate a long distance along the reinforcing steel bar are found to be sensitive to the interface conditions between steel bar and concrete. Ultrasonic transducers are used to launch and detect cylindrical guided waves along the steel bar. The traditional ultrasonic testing methods, for instance the pulse-echo method, where reflection, transmission, and scattering of longitudinal waves are used for detecting large voids in concrete, are not very efficient for detecting corrosion and delamination at the interface between concrete and steel bar. For this study four sets of specimens were prepared. They are rebars and plain steel bars with corrosion and physical separation. Transducers used during the experiment are the Electromagnetic Acoustic Transducer (EMAT) and the Piezoelectric Transducer (PZT). The experiment suggests that the guided wave inspection technique is feasible for the health monitoring of reinforced concrete structures. It also reveals that the ultrasonic guided waves are sensitive to the type of steel used and to the rib patterns on the reformed steel bars.
• Na, W. B., & Kundu, T. (2002). Underwater pipeline inspection using guided waves. JOURNAL OF PRESSURE VESSEL TECHNOLOGY-TRANSACTIONS OF THE ASME, 124(2), 196-200.
• Na, W. B., & Kundu, T. (2002). Wave attenuation in pipes and its application in determining axial spacing of monitoring sensors. Materials evaluation, 60(5), 635--644.
• Na, W. B., Kundu, T., & Ehsani, M. R. (2002). Ultrasonic guided waves for steel bar concrete interface testing. Ariel, 129, 31--248.
• Na, W. B., Kundu, T., & Ehsani, M. R. (2002). Ultrasonic guided waves for steel bar concrete interface testing. MATERIALS EVALUATION, 60(3), 437-444.
• Na, W., & Kundu, T. (2002). A combination of PZT and EMAT transducers for interface inspection. Journal of the Acoustical Society of America, 111(5 I), 2128-2139.
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  PMID: 12051433;Abstract: A PZT (Lead Zirconate-Titanate) transducer requires a couplant to send and receive mechanical waves. This requirement is a major shortcoming of the PZT technique for use in field applications. In the laboratory environment careful considerations and surface treatments are required to use PZT because the couplant can affect the consistency of experimental results. One alternative to overcome this shortcoming is the use of EMAT (ElectroMagnetic Acoustic Transducer). However, EMAT gives relatively low transmitted ultrasonic energy, with low signal to noise ratio, and the induced energy is critically dependent on the probe proximity to the test object. These are not desirable properties for NDT (nondestructive testing) of civil infrastructures. That is why, in this paper, a combination of PZT and EMAT is introduced for investigating reinforced concrete structures. Interface defects between steel bars and concrete are investigated by this technique. It is shown that the PZT-EMAT combination is very effective for steel bar-concrete interface inspection and the guided waves are useful for nondestructive testing of civil infrastructures. © 2002 Acoustical Society of America.
• Na, W., & Kundu, T. (2002). A combination of PZT and EMAT transducers for interface inspection. The Journal of the Acoustical Society of America, 111(5), 2128--2139.
• Na, W., & Kundu, T. (2002). EMAT-based inspection of concrete-filled steel pipes for internal voids and inclusions. Journal of Pressure Vessel Technology, Transactions of the ASME, 124(3), 265-272.
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  Abstract: Concrete-filled steel pipes have been used as piles for supporting civil and marine structures. These piles provide good bending resistance, and can be easily spliced for long depth installation. However, these piles are usually exposed in hostile environments such as seawater and deicing materials. Thus, the outside corrosion of the steel pipe can reduce the wall thickness and the corrosion-induced delamination of internal concrete can increase internal volume or pressure. In addition, the void that can possibly exist in the pipe reduces the bending resistance. To avoid structural failure due to this type of deterioration, appropriate inspection and repair techniques are to be developed. The acoustic method is attractive for this inspection since it is relatively simple and versatile. Especially, guided wave techniques have strong potentials for this inspection because of long-distance inspection capability. There are different transducer-coupling mechanisms available for the guided wave inspection techniques. Electro-magnetic acoustic transducers (EMATs) give relatively consistent results in comparison to piezoelectric transducers since they do not need any couplant. EMATs are used for transmitting and receiving cylindrical guided waves through concrete-filled steel pipes. It is shown that EMAT-generated cylindrical guided wave techniques have good potential for the interface inspection of concrete-filled steel pipes.
• Na, W., & Kundu, T. (2002). EMAT-based inspection of concrete-filled steel pipes for internal voids and inclusions. Journal of pressure vessel technology, 124(3), 265--272.
• Na, W., & Kundu, T. (2002). Underwater pipeline inspection using guided waves. Journal of Pressure Vessel Technology, Transactions of the ASME, 124(2), 196-200.
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  Abstract: Underwater pipeline inspections are conducted using ultrasonic cylindrical guided waves in the laboratory environment. Three different types of mechanical defects - gouge, removed metal, and dent - are fabricated in small-diameter, 22.22-mm, aluminum pipes and tested. To efficiently propagate the antisymmetric (flexural) cylindrical guided waves through the aluminum pipe in water, a new transducer holder device is designed. The device uses commercially available ultrasonic transducers that generate compressional ultrasonic waves in the water. The device can change the striking angle of the incident beam from 0 to 51 deg. With the help of this device, the incident angle adjustment and frequency sweeping can be carried out. This is necessary for obtaining the time history of the received signals for various incident angles and signal frequencies; then these time histories are converted to V(f) curves, or received signal amplitude versus frequency curves. From the amplitude of these V(f) curves, the type and extent of the mechanical defects can be estimated. This investigation shows that the new coupler device can be effectively used for health monitoring of underwater pipelines using guided waves.
• Na, W., & Kundu, T. (2002). Underwater pipeline inspection using guided waves. Journal of pressure vessel technology, 124(2), 196--200.
• Na, W., & Kundu, T. (2002). Wave attenuation in pipes and its application in determining axial spacing of monitoring sensors. Materials Evaluation, 60(5), 635-644.
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  Abstract: Wave attenuation in empty and water filled steel and concrete pipes is investigated. Several boundary conditions are considered in order to study the characteristics of phase velocity and attenuation dispersion curves. By examining wave attenuation dispersion curves, the axial spacing of monitoring sensors can be determined. This information is important for health monitoring of pipes.
• Na, W., Kundu, T., & Ehsani, M. R. (2002). Ultrasonic guided waves for steel bar concrete interface testing. Materials Evaluation, 60(3), 437-444.
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  Abstract: The feasibility of detecting and quantifying delamination at the interface between steel bar and concrete using ultrasonic guided waves is investigated in this paper. These waves can propagate a long distance along the reinforcing steel bar or concrete beam as guided waves and are sensitive to the interface bonding condition between the steel bar and concrete. The traditional ultrasonic methods are good for detecting large voids in concrete but not very efficient for detecting delamination at the interface between concrete and steel bar since they use reflection, transmission and scattering of longitudinal waves by internal discontinuities. In this study, special solid couplers between the steel bar (or concrete beam) and ultrasonic transducers have been used to launch flexural cylindrical guided waves (or lamb waves) in the steel bar (or concrete). This investigation shows that the guided wave testing technique is an efficient and effective tool for health monitoring of reinforced concrete structures.
• Na, W., Kundu, T., & Ryu, Y. (2002). Underwater inspection of concrete-filled steel pipes using guided waves. KSCE Journal of Civil Engineering, 6(1), 25--31.
• Placko, D., Kundu, T., & Ahmad, R. (2002). Theoretical computation of acoustic pressure generated by ultrasonic sensors in presence of an interface. Proceedings of SPIE - The International Society for Optical Engineering, 4702, 157-168.
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  Abstract: DPSM (Distributed Point Source Method) is a computational technique that can be used to model the pressure field generated by ultrasonic acoustic transducers. This technique involves discretization of the transducer face of any geometrical shape, into a number of elemental surface areas. Point sources are placed at the centroids of the elemental surface areas. The strengths of the point sources are proportional to the surface areas. Pressure field at a given point is the cumulative effect of the pressure fields generated by all point sources. The accuracy of the computational technique depends on the sensor surface discretization. In this paper, circular transducers are modeled using the DPSM technique. This technique is applied to calculate the pressure field distribution in non-homogeneous fluids with interface. The nonhomogeneous fluid is composed of two fluid half-spaces with the interface in front of the transducer face parallel or inclined to the transducer face. Pressure fields in both fluids for normal and angular incidence of the ultrasonic beam have been calculated using DPSM technique.
• Sen, A., Ghosh, B., Kundu, T. N., Das, S. K., & Sengupta SR, . (2002). Cerebrotendinous xanthomatosis.. The Journal of the Association of Physicians of India, 50, 1196.
• Towfighi, S., Kundu, T., & Ehsani, M. (2002). Elastic wave propagation in circumferential direction in anisotropic cylindrical curved plates. JOURNAL OF APPLIED MECHANICS-TRANSACTIONS OF THE ASME, 69(3), 283-291.
• Towfighi, S., Kundu, T., & Ehsani, M. (2002). Elastic wave propagation in circumferential direction in anisotropic cylindrical curved plates. Journal of Applied Mechanics, Transactions ASME, 69(3), 283-291.
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  Abstract: Ultrasonic nondestructive inspection of large-diameter pipes is important for health monitoring of ailing infrastructure. Longitudinal stress-corrosion cracks are detected more efficiently by inducing circumferential waves; hence, the study of elastic wave propagation in the circumferential direction in a pipe wall is essential. The current state of knowledge lacks a complete solution of this problem. Only when the pipe material is isotropic a solution of the wave propagation problem in the circumferential direction exists. Ultrasonic inspections of reinforced concrete pipes and pipes retrofitted by fiber composites necessitate the development of a new theoretical solution for elastic wave propagation in anisotropic curved plates in the circumferential direction. Mathematical modeling of the problem to obtain dispersion curves for curved anisotropic plates leads to coupled differential equations. Unlike isotropic materials for which the Stokes-Helmholtz decomposition technique simplifies the problem, in anisotropic case no such general decomposition technique works. These coupled differential equations are solved in this paper. Dispersion curves for anisotropic curved plates of different curvatures have been computed and presented. Some numerical results computed by the new technique have been compared with those available in the literature.
• Towfighi, S., Kundu, T., & Ehsani, M. (2002). Elastic wave propagation in circumferential direction in anisotropic cylindrical curved plates. Journal of applied mechanics, 69(3), 283--291.
• Darvennes, C., & Kundu, T. (2001). American Society of Mechanical Engineers (Publication) NDE: Foreword. American Society of Mechanical Engineers (Publication) NDE, 20, iii.
• Desai, C. S., & Kundu, T. (2001). Introductory finite element method.
• Guo, D., & Kundu, T. (2001). A new transducer holder mechanism for pipe inspection. Journal of the Acoustical Society of America, 110(1), 303-309.
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  Abstract: A new transducer holder mechanism has been designed and fabricated for pipe inspection by cylindrical guided waves. Commercially available ultrasonic transducers have been used to generate compressional ultrasonic waves in the coupling medium. Those waves are converted to cylindrical guided waves in the pipe by the new coupling mechanism. A number of advanced coupling mechanisms developed recently for large plate and pipe inspection require the presence of a coupling fluid between the ultrasonic transducer and the pipe or plate specimen. These mechanisms can be used for inspecting horizontal pipes and plates. The new coupling mechanism presented in this article uses solid material as the coupler and can be used equally well for inspecting horizontal as well as inclined or vertical pipes. The new coupling mechanism has been designed to generate efficiently different Lamb modes in the pipe. The new design has been used to inspect different kinds of anomalies in copper and aluminum pipes. The preliminary results show that a number of Lamb modes, when generated properly by the new coupling mechanism, are very sensitive to the pipe defects. These experimental results along with the new design of the coupling mechanism are presented in this article. © 2001 Acoustical Society of America.
• Jung, Y. -., & Kundu, T. (2001). Ultrasonic response to material fatigue. Proceedings of SPIE - The International Society for Optical Engineering, 4335, 180-187.
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  Abstract: In many engineering materials micro-cracks develop when the materials are subjected to repeated loading or fatigue loading. These micro-cracks increase the material attenuation and alter the ultrasonic wave speed. Careful experiments show that as a material is subjected to a greater number of fatigue cycles, its higher order (also known as the nonlinear) acoustic properties change significantly. The percentage change in the nonlinear acoustic properties is greater than the percentage changes in the wave speed and attenuation. However, experimentally it is very difficult to measure these nonlinear acoustic properties. Materials like concrete develop a large number of micro-cracks under fatigue loading and show measurable changes in its attenuation. However, some other materials, such as Plexiglas, apparently do not develop micro-cracks under fatigue loading. They look same, equally transparent, before and after the repeated loading up to the point of its failure. Its longitudinal wave speed and attenuation also do not change by any measurable amount due to the fatigue loading. Changes in the nonlinear ultrasonic properties are too difficult to measure. Can there be any relatively robust ultrasonic measurement to capture the property changes in such materials due to fatigue loading? It is investigated in this paper. It is found that some guided wave propagation characteristics change with fatigue loading. These changes are strong enough to be detected by ordinary ultrasonic measurements without taking help of any highly precise ultrasonic measuring instrument in the experimental setup.
• Jung, Y. C., Kundu, T., & Ehsani, M. (2001). Internal Discontinuity Detection in Concrete by Lamb Waves. Materials Evaluation, 59(3), 418-423.
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  Abstract: The feasibility of detecting anomalies or discontinuities in concrete beams using lamb waves is investigated in this paper. The traditional ultrasonic methods for inspecting discontinuities in concrete use the reflection, transmission and scattering of longitudinal waves by internal discontinuities. Signal amplitude and time of flight measurements provide information about the internal anomalies in concrete. However, these methods are time consuming and, as will be shown in this paper, the traditional techniques often fail to detect honeycombs, dosed cracks and small anomalies. In this paper the potential of the lamb wave technique to detect those anomalies in large concrete beams is investigated. The lamb wave technique is found to be reliable for detecting such anomalies.
• Jung, Y. C., Kundu, T., & Ehsani, M. (2001). Internal discontinuity detection in concrete by Lamb waves. Materials evaluation, 59(3), 418--423.
• Jørgensen, C., Hasenkam, J. M., & Kundu, T. (2001). Measurement of material properties of hard and soft biological tissues by means of V(z) and V(f) curves obtained with acoustic microscopy. Proceedings of SPIE - The International Society for Optical Engineering, 4335, 244-253.
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  Abstract: Measurement of acoustic propagation speed (C) and attenuation (α) in biological tissues serves to enhance our understanding of how tissue composition and structure affects organ function. We applied the V(z)-technique to measurement of C in embedded cancellous bone at 1 GHz using an acoustic microscope and succeeded in recording the Cs of both longitudinal lateral waves (CL) and Rayleigh waves (CR). The former ranged between 2.33 and 4.33 km/s (mean ±SD: 3.37 ±0.61 km/s) and the latter between 1.93 and 2.07 km/s (2.00 ±0.06 km/s), which is in the range expected on the basis of known properties of bone and acoustic field theory. With respect to soft tissue sections, the V(z)-technique is practically impossible to use, and therefore we applied the V(f)-technique to sections of chordae tendineae. Initial measurements of C and α of aortic tissue, which is well characterized, showed a C of 1.59 ±0.04km/s and α of 0.230 ±0.001 dB/μm at signal frequencies 0.95 to 1.02 GHz. These results were in agreement with those of others and the chordae subsequently revealed a mean C of 1.79 ±0.18 km/s and α of 0.220 ±0.010 dB/μm. The distribution of the properties across the chordal sections showed a regularly undulating pattern which followed the undulating pattern of the collagen fiber arrangement. We conclude that the V(z)- and V(f)-technique are both valuable techniques for microelastic characterization of biological tissues.
• Keller, M. S., Kundu, T., & Desai, C. S. (2001). Use of lamb waves to predict current damaged state of mortar. American Society of Mechanical Engineers (Publication) NDE, 21, 9-20.
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  Abstract: This paper describes the experimental and analytical results for the development of a methodology for predicting the current state of simulated concrete (mortar) in infrastructure. The nondestructive Lamb wave technique is used to experimentally identify the disturbance (damage) before and after mechanical testing of mortar specimens, which is used in the initial research as a substitute for concrete. The mortar specimens are tested to measure their stress-strain response under uniaxial compression and tension loading. The results of the nondestructive and mechanical stress-strain testing are correlated to develop the model based on the Disturbed State Concept (DSC), a unified approach for modeling material behavior. This model can allow evaluation of the deformation moduli, strength and degredation (damage) at a given state during the life of the material. This information can be used to design rehabilitation strategies. It can also lead to the development of new computer based equipment that can be used in the field for defining the remaining life. At this time, the research involved one-dimensional testing. The proposed methodology can, however, be extended and improved by conducting two- and three-dimensional testing of concrete specimens.
• Kundu, T. (2001). Advanced nondestructive evaluation for structural and biological health monitoring; Proceedings of the Conference, Newport Beach, CA, Mar. 6-8, 2001. Bellingham, WA, Society of Photo-Optical Instrumentation Engineers(SPIE Procedings., 4335.
• Kundu, T. (2001). Proceedings of SPIE: Advanced Nondestructive Evaluation for Structural and Biological Health Monitoring, Newport Beach, USA, 6-8 March 2001: Introduction. Proceedings of SPIE - The International Society for Optical Engineering, 4335, xi.
• Kundu, T., & Jørgensen, C. S. (2001). Importance of multiply reflected signals in V(z) curve analysis for material characterization by acoustic microscopes. American Society of Mechanical Engineers (Publication) NDE, 20, 99-105.
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  Abstract: Acoustic microscopes can be used to measure Rayleigh and longitudinal or P-wave speeds in a specimen at microscopic resolution. The wave speeds are obtained from the interference pattern as a function of the defocus distance or V(z) curve. The received signal voltage amplitude Vis generated by two beams - the normally reflected central beam and a non-specularly reflected beam that strikes the fluid-solid interface at critical angle. It is shown in this paper that instead of analyzing the interference pattern between these two beams if we consider two other beams that follow the same path but travel through the coupling fluid multiple times before interfering then the V(z) curve generated by this higher order interference gives more accurate values for the material properties. The spacing distance between two successive dips of the V(z) curve is smaller for the higher order interference. The higher order interference, although weaker, gives more accurate results. Justification for the greater accuracy of the higher order interference is given in the paper. Material properties of silicon and bone are obtained by the new technique.
• Kundu, T., Potel, C., & Belleval, J. D. (2001). Importance of the near Lamb mode imaging of multilayered composite plates. Ultrasonics, 39(4), 283-290.
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  PMID: 11432438;Abstract: In recent years Lamb waves are being used for internal defect detection in multilayered composite plates. Different Lamb modes generate various stress levels in different layers. As a result, all Lamb modes are not equally sensitive to internal defects of various layers. A number of studies have been carried out to identify which Lamb mode is most effective for detecting defects in a specific layer. However, one shortcoming of the Lamb wave inspection technique is that in a symmetrically layered composite plate stress and displacement magnitudes and energy distribution profiles for all Lamb modes are symmetric about the central plane of the plate. As a result, the ability of a Lamb mode to detect defects in a specific layer of the plate is identical to its ability to detect defects in the corresponding layer of mirror symmetry. Hence, from the Lamb wave generated image one cannot distinguish between the defects in these two layers of mirror symmetry. In this paper it is investigated how by fine-tuning the frequency and the striking angle of the incident beam in the neighborhood of a Lamb mode one can separately detect internal defects in layers of mirror symmetry in the upper and lower halves of a plate. © 2001 Elsevier Science B.V.
• Na, W., & Kundu, T. (2001). Underwater pipeline inspection using guided waves. American Society of Mechanical Engineers (Publication) NDE, 21, 37-47.
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  Abstract: Underwater pipeline inspections are conducted using ultrasonic cylindrical guided waves in the laboratory environment. Three different types of mechanical defects - gouge, removed metal, and dent, are fabricated in small diameter, 22.22 mm, aluminum pipes and tested. To efficiently propagate the antisymmetric (flexural) cylindrical guided waves through the aluminum pipe in water, a new transducer holder device is designed. The device uses commercially available ultrasonic transducers that generate compressional ultrasonic waves in the water. The device can change the striking angle of the incident beam from 0° to 51°. With the help of this device the incident angle adjustment and frequency sweeping can be carried out. This is necessary for obtaining the time history of the received signals for various incident angles and signal frequencies; then these time histories are converted to V(f) curves, or received signal amplitude vs. frequency curves. From the amplitude of these V(f) curves the type and extent of the mechanical defects can be estimated. This investigation shows that the new coupler device can be effectively used for health monitoring of underwater pipelines using guided waves.
• Na, W., Kundu, T., & Ryu, Y. (2001). Cylindrical guided waves for inspection of clay-steel pile interface. KSCE Journal of Civil Engineering, 5(1), 29--34.
• Placko, D., & Kundu, T. (2001). A theoretical study of magnetic and ultrasonic sensors: Dependence of magnetic potential and acoustic pressure on the sensor geometry. Proceedings of SPIE - The International Society for Optical Engineering, 4335, 52-62.
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  Abstract: In this paper, we describe a model based on a spatial distribution of point sources, called "DPSM" (Distributed Point Sources Method), applied to magnetic and ultrasonic sensors modelling. Magnetic and acoustic fields are theoretically generated for two types of sensors. The sensor surface is discretized into a finite number of elemental surfaces. A point source is placed at the centroid position of every elemental surface. Point source strength is proportional to the elemental surface area for acoustic sensors and it is obtained by inverting a matrix to satisfy the equipotential boundary conditions for magnetic sensors. Total field is computed at a given point by adding fields generated by all sources. The main difference between the magnetic and acoustic field modelling is that for a magnetic sensor the magnetic potential remains constant on the sensor surface and the magnetic flux varies from point to point, while for the acoustic sensor the particle velocity remains constant on the sensor surface and the acoustic pressure varies. This difference causes an additional matrix inversion in the magnetic field modelling, which is not necessary for the acoustic field modelling. Like other numerical modelling schemes, accuracy of the computation depends on the sensor surface discretization or mesh generation. Effect of the spacing between two neighbouring point sources on the accuracy of the field computation is studied and the optimum spacing for accurate numerical computation is given. For accurately modelling acoustic fields the spacing between two neighbouring sources should be less than the acoustic wavelength. Flat sensors with circular and rectangular cross-sections as well as point focused concave sensors have been modelled by this technique.
• Towfighi, S., Kundu, T., & Ehsani, M. (2001). Elastic wave propagation in circumferential direction in anisotropic pipes. American Society of Mechanical Engineers (Publication) NDE, 21, 29-36.
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  Abstract: Ultrasonic nondestructive inspection of large diameter pipes is important for health monitoring of ailing infrastructure. Longitudinal stress-corrosion cracks are detected more efficiently by inducing circumferential waves; hence, the study of elastic wave propagation in the circumferential direction of a pipe is essential. The current state of knowledge lacks a complete solution of this problem. Only when the pipe material is isotropic a solution of the wave propagation problem in the circumferential direction exists. Ultrasonic inspections of reinforced concrete pipes and pipes retrofitted by fiber composites necessitate the development of a new theoretical solution for elastic wave propagation in anisotropic pipes in the circumferential direction. Mathematical modeling of the problem to obtain dispersion curves for anisotropic materials leads to coupled differential equations. Unlike isotropic materials for which the Stokes-Helmholtz decomposition technique simplifies the problem, in anisotropic case no such general decomposition technique works. These coupled differential equations are solved in this paper. Dispersion curves for anisotropic pipes of different curvatures have been computed and presented. Some numerical results computed by the new technique have been compared with those available in the literature.
• Castaings, M., Hosten, B., & Kundu, T. (2000). Inversion of ultrasonic, plane-wave transmission data in composite plates to infer viscoelastic material properties. NDT & E INTERNATIONAL, 33(6), 377-392.
• Castaings, M., Hosten, B., & Kundu, T. (2000). Inversion of ultrasonic, plane-wave transmission data in composite plates to infer viscoelastic material properties. NDT & E International, 33(6), 377--392.
• Castaings, M., Hosten, B., & Kundu, T. (2000). Inversion of ultrasonic, plane-wave transmission data in composite plates to infer viscoelastic material properties. NDT and E International, 33(6), 377-392.
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  Abstract: Stiffness and damping properties of viscoelastic materials are given by the real and imaginary components, respectively, of the material constants. A new technique is proposed to experimentally measure the real and imaginary components of anisotropic (and isotropic) viscoelastic plates. Main advantage of this technique is that material properties of thin plates can be measured where many other techniques fail. Material properties are obtained by numerically inverting the transmitted ultrasonic fields, obtained for different incident angles. Simplex inversion algorithm is applied to initial estimates of plate thickness and plate properties. By this iterative technique the values of the unknown parameters (material properties and plate thickness) are continuously modified to give better agreement between the experimental and theoretical transmitted fields. After a certain number of iterations the speed of convergence of the Simplex scheme is significantly reduced. To improve the accuracy of convergence the Newton-Raphson inversion technique is adopted at that point. By this technique material properties of different types of plates are measured. These is a glass plate (isotropic plate with no damping), a polymer plate (isotropic plate with damping), and glass fiber reinforced epoxy plates with different fiber orientations (anisotropic plates with damping). Both real and imaginary components are successfully measured for all these plates. In a relative scale the measurement error for the imaginary components is higher. Reliability of the measured material constants of fiber reinforced epoxy plates is verified by the method of invariance. All experiments are carried out in the frequency range that is appropriate for satisfying two conditions - the specimen homogeneity and the plane wave conditions.
• Guo, D., & Kundu, T. (2000). A New Sensor for Pipe Inspection by Lamb Waves. Materials Evaluation, 58(8), 991-994.
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  Abstract: Efficient inspection for internal damage of long pipelines in the chemical and power industries is a challenging task. It becomes even more difficult if the pipes are coated with insulating materials. With traditional methods insulation coatings are removed at selected places and the pipe wall thicknesses at these spots are measured using ultrasonic transducers. A sudden drop in the pipe wall thickness indicates the possibility of corrosion damage. This is a time consuming and expensive operation. The lamb wave inspection technique proposed in this paper is a much more efficient technique because it allows long pipes to be inspected by removing insulation at only few places. One can detect anomalies inside the pipe wall at a specific depth by correctly selecting a lamb mode and propagating that mode through the pipe. This technique is described in this paper. A new sensor has been designed and fabricated for efficiently generating different lamb modes in the pipe. Sensitivity of the lamb modes to different types of anomalies in the pipe has been investigated.
• Guo, D., & Kundu, T. (2000). A new sensor for pipe inspection by Lamb waves. Materials Evaluation, 58(8), 991--994.
• Guo, D., & Kundu, T. (2000). Lamb wave sensors for detecting wall defects in pipes. Proceedings of SPIE - The International Society for Optical Engineering, 3995, 610-618.
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  Abstract: A number of sensors have been designed and fabricated for pipeline inspection. These sensors require commercially available ultrasonic transducers but use a new coupling mechanism. Some of these sensors require the presence of a coupling fluid between the ultrasonic transducer and the pipe. These sensors can inspect horizontal pipes. Other sensors use solid coupling medium and can be used equally well for inspecting horizontal, vertical or inclined pipes. Our objective is to generate different modes of the cylindrical guided waves in pipes. The new coupling mechanisms have been designed to generate different axisymmetric and non-axisymmetric Lamb modes in the pipe by changing the excitation frequency, inclination angle and number of transmitters. These Lamb wave sensors have been used to inspect a number of defect-free and defective pipes. The preliminary results show that these sensors can detect the pipe defects even when the defects are located at a distance. A comparison between the degree of damage and the Lamb wave generated received signal shows that a correlation exists between the two. Hence, this technique can be used for detecting the pipe damage as well as for predicting its degree of damage. Experimental results are presented to justify this claim.
• Jung, Y., Na, W., Kundu, T., & Ehsani, M. (2000). Damage detection in concrete using Lamb waves. Proceedings of SPIE - The International Society for Optical Engineering, 3995, 448-458.
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  Abstract: The feasibility of detecting defects in concrete beams using Lamb waves is investigated in this paper. The Lamb wave can propagate a long distance along the specimen as the guided wave and is sensitive to defects that are smaller than its wavelength. The traditional ultrasonic methods for inspecting defects in concrete use reflection, transmission and scattering of longitudinal waves by internal defects. In traditional techniques signal amplitude and time of flight measurements provide information about the internal defects in concrete. These methods are time consuming and often fail to detect a variety of defects, such as internal corrosion, honeycombs, closed cracks and small inclusions. In this paper Lamb waves are used to detect those defects in concrete beams with and without reinforcement. The Lamb wave technique is found to be reliable for detecting such defects. The effect of separation or delamination between concrete and reinforcing steel bars on the Lamb wave propagation characteristics is also investigated. Corrosion of rebars can cause this delamination. It is found that the cylindrical guided waves propagating along the steel rebars are very sensitive to the degree of delamination between the concrete and the rebars. This investigation shows that the Lamb wave inspection technique is an efficient and effective tool for health monitoring of concrete structures.
• Kundu, T. (2000). FEATURES-ARE SMART PIGS AN ENDANGERED SPECIES?-Details of a report by Tribikram Kundu says a new system may replace smart pigs.. Gas-Utility and Pipeline Industries, 44(12), 24--24.
• Kundu, T. (2000). Techniques for Material. Modeling in geomechanics, 267.
• Kundu, T., & Jorgensen, C. (2000). Acoustic microscopy for bone characterization. American Society of Mechanical Engineers (Publication) NDE, 13-30.
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  Abstract: Characterization of animal bones by acoustic microscopy is a relatively new field of research. Non-uniformity of bones requires a complete analysis of the interaction between the focused acoustic beam and the bone specimens for its characterization. The complete analysis produces the V(z) curve taking into account the lens angle and the elastic properties of the bone. V(z) oscillations may be generated by surface skimming Rayleigh waves and/or P-waves in different parts of the bone depending on the bone properties. In this paper after a short review of different applications of the acoustic microscopy technique a complete theory of the V(z) curve synthesis is briefly presented. A number of V(z) curves are analytically generated following this theory. These curves sometimes show a regular oscillatory shape as predicted by the simple ray theory. However, often the synthesized V(z) curves show irregularities. The synthesized V(z) curve for silicon has been compared with the experimental results to have a confidence on the analytical computation. Then additional numerical exercises are carried out to understand why sometimes the V(z) curve shapes are irregular, and whether the P-wave speed and/or the Rayleigh wave speed of the material can be extracted from such irregular shaped V(z) curves. After understanding the V(z) phenomenon the wave speeds at different points of a bone are experimentally measured from its V(z) curves.
• Kundu, T., & Jorgensen, C. (2000). Acoustic microscopy for bone characterization. American Society of Mechanical Engineers, Applied Mechanics Division, AMD, 240, 13-30.
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  Abstract: Characterization of animal bones by acoustic microscopy is a relatively new field of research. Non-uniformity of bones requires a complete analysis of the interaction between the focused acoustic beam and the bone specimens for its characterization. The complete analysis produces the V(z) curve taking into account the lens angle and the elastic properties of the bone. V(z) oscillations may be generated by surface skimming Rayleigh waves and/or P-waves in different parts of the bone depending on the bone properties. In this paper after a short review of different applications of the acoustic microscopy technique a complete theory of the V(z) curve synthesis is briefly presented. A number of V(z) curves are analytically generated following this theory. These curves sometimes show a regular oscillatory shape as predicted by the simple ray theory. However, often the synthesized V(z) curves show irregularities. The synthesized V(z) curve for silicon has been compared with the experimental results to have a confidence on the analytical computation. Then additional numerical exercises are carried out to understand why sometimes the V(z) curve shapes are irregular, and whether the P-wave speed and/or the Rayleigh wave speed of the material can be extracted from such irregular shaped V(z) curves. After understanding the V(z) phenomenon the wave speeds at different points of a bone are experimentally measured from its V(z) curves.
• Kundu, T., Bereiter-Hahn, J., & Karl, I. (2000). Cell property determination from the acoustic microscope generated voltage versus frequency curves. BIOPHYSICAL JOURNAL, 78(5), 2270-2279.
• Kundu, T., Bereiter-Hahn, J., & Karl, I. (2000). Cell property determination from the acoustic microscope generated voltage versus frequency curves. Biophysical Journal, 78(5), 2270-2279.
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  PMID: 10777725;PMCID: PMC1300818;Abstract: Among the methods for the determination of mechanical properties of living cells acoustic microscopy provides some extraordinary advantages. It is relatively fast, of excellent spatial resolution and of minimal invasiveness. Sound velocity is a measure of the stiffness or Young's modulus of the cell. Attenuation of cytoplasm is a measure of supramolecular interactions. These parameters are of crucial interest for studies of cell motility, volume regulations and to establish the functional role of the various elements of the cytoskeleton. Using a phase and amplitude sensitive modulation of a scanning acoustic microscope (Hillman et al., 1994, J. Alloys Compounds. 211/212:625-627) longitudinal wave speed, attenuation and thickness profile of a biological cell are obtained from the voltage versus frequency or V(f) curves. A series of pictures, for instance in the frequency range 980-1100 MHz with an increment of 20 MHz, allows the experimental generation of V(f) curves for each pixel while keeping the lens-specimen distance unchanged. Both amplitude and phase values of the V(f) curves are used for obtaining the cell properties and the cell thickness profile. The theoretical analysis shows that the thin liquid layer, between the cell and the substrate, has a strong influence on the reflection coefficient and should not be ignored during the analysis. Cell properties, cell profile and the thickness of the thin liquid layer are obtained from the V(f) curves by the simplex inversion algorithm. The main advantages of this new method are that imaging can be done near the focal plane, therefore an optimal signal to noise ratio is achieved, no interference with Rayleigh waves occurs, and the method requires only an approximate estimate of the material properties of the solid substratum where the cells are growing on.
• Kundu, T., Jang, H. S., Cha, Y. H., & Desai, C. S. (2000). A simple model to predict the effect of volume fraction, diameter, and length of fibres on strength of fibre reinforced brittle matrix composites. International Journal for Numerical and Analytical Methods in Geomechanics, 24(7), 655-673.
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  Abstract: A simplified model is presented to predict the strength variations of brittle matrix composites, reinforced by steel fibres, with the variations of fibre parameters-length, diameter and volume fraction. This model predicts that its tensile and flexural strength increase non-linearly with the fibre volume fraction. It also predicts that similar non-linear behaviour should be observed with the reduction of the fibre diameter when other parameters are kept constant. The experimental results support both these theoretical predictions. It is also explained why an increase in the fibre length does not always significantly increase the fracture toughness. The objective of this paper is not to explain and understand in great detail the science of all phenomena responsible for the strength increase of fibre reinforced brittle matrix composites, but to provide a simple engineering explanation as to why its strength increases with the fibre addition, and how this increase can be quantitatively related to the variations in fibre parameters-fibre volume fraction, fibre length and diameter. These simplifying steps are needed to provide a tool that the practicing engineers can use to predict the brittle matrix strength variation with the fibre parameters. In the area of geomechanics, the results presented here can be used to assess and predict the behaviour of fibre-reinforced earth. Copyright (C) 2000 John Wiley and Sons, Ltd.
• Kundu, T., Potel, C., & Belleval, J. d. (2000). Near Lamb mode imaging of multilayered composite plates. Proceedings of SPIE - The International Society for Optical Engineering, 3994, 174-183.
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  Abstract: Lamb waves have been used for internal defect detection in multilayered composite plates. Different Lamb modes generate various stress levels in different layers. As a result, all Lamb modes are not equally sensitive to internal defects located in different layers. A number of studies have been carried out to identify which Lamb mode is most effective for detecting defects in a specific layer. However, one shortcoming of the Lamb wave inspection technique is that in a symmetrically layered composite plate stress and displacement magnitudes and energy distribution profiles for all Lamb modes are symmetric about the central plane of the plate. As a result, the ability of a Lamb mode to detect defects in a specific layer of the plate is identical to its ability to detect defects in the corresponding layer of mirror symmetry. Hence, from the Lamb wave generated image one cannot distinguish between the defects in two layers of mirror symmetry. In this paper it is investigated how by fine-tuning the frequency and the striking angle of the incident beam in the neighborhood of a Lamb mode one can separately detect internal defects in layers of mirror symmetry in the upper and lower halves of a plate.
• Na, W., Kundu, T., & Ehsani, M. R. (2000). Inspection of concrete-metal rod interface using guided waves. American Society of Mechanical Engineers (Publication) NDE, 59-64.
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  Abstract: The feasibility of detecting interface degradation and separation of steel rebars in concrete beams using Lamb waves is investigated in this paper. It is shown that Lamb waves can easily detect these defects. A special coupler between the steel rebar and ultrasonic transducers has been used to launch non-axisymmetric guided waves in the steel rebar. This investigation shows that the Lamb wave inspection technique is an efficient and effective tool for health monitoring of reinforced concrete structures because the Lamb wave can propagate a long distance along the reinforcing steel bars embedded in concrete as the guided wave and is sensitive to the interface debonding between the steel rebar and concrete.
• Na, W., Kundu, T., & Ehsani, M. R. (2000). Inspection of concrete-metal rod interface using guided waves. American Society of Mechanical Engineers, Applied Mechanics Division, AMD, 240, 59-64.
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  Abstract: The feasibility of detecting interface degradation and separation of steel rebars in concrete beams using Lamb waves is investigated in this paper. It is shown that Lamb waves can easily detect these defects. A special coupler between the steel rebar and ultrasonic transducers has been used to launch non-axisymmetric guided waves in the steel rebar. This investigation shows that the Lamb wave inspection technique is an efficient and effective tool for health monitoring of reinforced concrete structures because the Lamb wave can propagate a long distance along the reinforcing steel bars embedded in concrete as the guided wave and is sensitive to the interface debonding between the steel rebar and concrete.
• Jung, Y. C., Kundu, T., & Ehsani, M. (1999). Lamb wave inspection of concrete beams. American Society of Mechanical Engineers, Applied Mechanics Division, AMD, 234, 33-46.
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  Abstract: The feasibility of detecting defects in concrete beams using Lamb waves is investigated in this paper. The traditional ultrasonic methods for inspecting defects in concrete use the reflection and scattering of longitudinal waves by internal defects. Signal amplitude and time of flight measurements provide information about the internal defects in concrete. However, these methods are time consuming and often fail to detect honeycombs, closed cracks and small defects. In this paper the potential of the Lamb wave technique to detect those defects in large concrete beams is investigated. The Lamb wave technique is found to be reliable for detecting such defects in concrete beams.
• Kundu, T. (1999). Sliding Friction Physical Principles and Applications, BNJ Persson, Springer, Berlin, ISBN 1434-4904, ISBN 3-540-63296-4, 462 pp.. International Journal for Numerical and Analytical Methods in Geomechanics, 23(10), 1067--1068.
• Kundu, T., Ehsani, M., Maslov, K. I., & Guo, D. (1999). C-scan and L-scan generated images of the concrete/GFRP composite interface. NDT & E International, 32(2), 61--69.
• Kundu, T., Ehsani, M., Maslov, K. I., & Guo, D. (1999). C-scan and L-scan generated images of the concrete/GFRP composite interface. NDT and E International, 32(2), 61-69.
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  Abstract: Glass Fiber Reinforced Plastics (GFRP) are fast becoming a viable new construction material. They are being used for rehabilitating old concrete structures - columns, beams, slabs and walls - by gluing the composite plate to the concrete surface. Proper attachment between the GFRP plate and the concrete surface is necessary for efficient use of GFRP composites to increase the strength of the rehabilitated structures. Delamination between the rehabilitated structure and the GFRP plate significantly reduces the strength of the reinforced structure. Hence, delamination defects, if present at the interface, should be detected as soon as possible. In this paper, two ultrasonic techniques to detect delamination defects between the GFRP plate and the concrete surface are presented. One technique uses longitudinal waves or P-waves and the second technique uses Lamb waves. It is found that both techniques can detect the defect when used properly. However, Lamb waves give a better image quality of the defect than longitudinal waves. © 1998 Elsevier Science Ltd.
• Basaran, C., Desai, C. S., & Kundu, T. (1998). Thermomechanical Finite Element Analysis of Problems in Electronic Packaging Using the Disturbed State Concept: Part 1 - Theory and Formulation. Journal of Electronic Packaging, Transactions of the ASME, 120(1), 41-47.
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  Abstract: Accurate prediction of the thermomechanical cyclic behavior of joints and interfaces in semiconductor devices is essential for their reliable design. In order to understand and predict the behavior of such interfaces there is a need for improved and unified constitutive models that can include elastic, inelastic, viscous, and temperature dependent microstructural behavior. Furthermore, such unified material models should be implemented in finite element procedures so as to yield accurate and reliable predictions of stresses, strains, deformations, microcracking, damage, and number of cycles to failure due to thermomechanical loading. The main objective of this paper is to present implementation of such an unified constitutive model in a finite element procedure and its application to typical problems in electronic packaging; details of the constitutive model are given by Desai et al. (1995). Details of the theoretical formulation is presented in this Part 1, while its applications and validations are presented in Part 2, Basaran et al. (1998).
• Basaran, C., Desai, C. S., & Kundu, T. (1998). Thermomechanical Finite Element Analysis of Problems in Electronic Packaging Using the Disturbed State Concept: Part 1—Theory and Formulation. Journal of Electronic Packaging, 120(1), 41--47.
• Basaran, C., Desai, C. S., & Kundu, T. (1998). Thermomechanical Finite Element Analysis of Problems in Electronic Packaging Using the Disturbed State Concept: Part 2 - Verification and Application. Journal of Electronic Packaging, Transactions of the ASME, 120(1), 48-53.
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  Abstract: The finite element procedure with the unified disturbed state modeling concept presented in Part I, Basaran et al. (1998), is verified here with respect to laboratory test results for Pb40/Sn60 eutectic solder alloy. This solder alloy is a commonly used interconnection material for surface mount technology packages. It is demonstrated that the proposed procedure provides highly satisfactory correlation with the observed laboratory behavior of materials and with test results for a chip-substrate system simulated in the laboratory.
• Bereiter-Hahn, J., Hetche, R., Karl, I., Molodykh, A., & Kundu, T. (1998). Cellular Responses to Mechanical Stimulation. ASME APPLIED MECHANICS DIVISION-PUBLICATIONS-AMD, 229, 97--98.
• Das, S. K., Sinha, I., Kundu, T. N., Sanyal, K., Santosh, V., & Shankar, S. K. (1998). Two cases of neurosarcoidosis presenting as peripheral neuropathy and stroke in young.. The Journal of the Association of Physicians of India, 46(5), 479.
• Ghosh, T., & Kundu, T. (1998). A new transducer holder mechanism for efficient generation and reception of Lamb modes in large plates. Journal of the Acoustical Society of America, 104(3 I), 1498-1502.
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  Abstract: A new transducer holder mechanism is described in this paper. This mechanism is very useful for inspecting large plates by Lamb waves. The new mechanism allows water coupling between the ultrasonic transducers and the specimen but requires neither a water jet nor a big water tank for immersing the specimen into it. This mechanism allows the transducers to rotate for changing the angle of strike of the incident beam and avoids undesirable multiply-reflected signals between the transducer and the specimen. An aluminum plate with fabricated internal defects has been inspected by the Lamb wave technique using the new transducer holder mechanism. The experimental results clearly show the superiority of the new design when compared with the conventional designs available today.
• Ghosh, T., & Kundu, T. (1998). A new transducer holder mechanism for efficient generation and reception of Lamb modes in large plates. The Journal of the Acoustical Society of America, 104(3), 1498--1502.
• Ghosh, T., Kundu, T., & Karpur, P. (1998). Efficient use of Lamb modes for detecting defects in large plates. ULTRASONICS, 36(7), 791-801.
• Ghosh, T., Kundu, T., & Karpur, P. (1998). Efficient use of Lamb modes for detecting defects in large plates. Ultrasonics, 36(7), 791-801.
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  Abstract: In this paper, Lamb wave propagation in large plates and its use in internal defect detection have been studied. The Lamb modes which are most efficient for detecting different types of internal defects are identified. Stress fields inside the plate for different Lamb modes are computed. From these stress plots one can conclude which Lamb mode should be efficient for detecting which type of material defect. Theoretical predictions are experimentally verified. © 1998 Elsevier Science B.V. All rights reserved.
• Kundu, T. (1998). microscopy. J. Microsc. 158: 95-107 [3] Hillmann K, Bereiter-Hahn J., Grill W.(1994) Acoustic microscopy with phase and amplitude sensitivity.. ASME Applied Mechanics Division Book of Abstracts, 158, 101.
• Kundu, T., Bereiter-Hahn, J., Karl, I., Hillmann, K., & Vesely, F. (1998). Determination of Mechanical Properties of Living Cells by V (f) Characteristics in the GHz Range Using Phase Sensitive Scanning Acoustic Microscopy. ASME APPLIED MECHANICS DIVISION-PUBLICATIONS-AMD, 229, 101--102.
• Kundu, T., Maji, A., Ghosh, T., & Maslov, K. (1998). Detection of kissing bonds by Lamb waves. ULTRASONICS, 35(8), 573-580.
• Kundu, T., Maji, A., Ghosh, T., & Maslov, K. (1998). Detection of kissing bonds by Lamb waves. Ultrasonics, 35(8), 573-580.
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  Abstract: Closed cracks under compressive normal stresses are difficult to detect by the conventional ultrasonic techniques. When the crack surfaces stay in very close contact with each other then the bond between the two surfaces of the crack is called a 'kissing bond'. This is a very dangerous bond. Catastrophic failures can result if the system is subjected to crack opening normal stresses or shear stresses. When the crack surfaces are smooth then kissing bonds cannot transmit shear stress very well but can carry compressive normal stress, these bonds are called 'slip bonds'. Conventional P-wave scans (C-scan or A-scan) are based on the assumptions that P-waves are reflected by the defective interface. However, an interface subjected to a large compressive stress cannot reflect P-waves effectively, hence these bonds remain invisible to the conventional P-wave based C-scan or A-scan techniques. In this paper it is shown that the kissing bonds can be effectively detected by some leaky Lamb mode. Theoretical and experimental results are presented to show that using the Lamb waves is an effective way of detecting kissing bonds. © 1998 Elsevier Science B.V.
• Yang, W., & Kundu, T. (1998). Guided waves in multilayered plates for internal defect detection. Journal of Engineering Mechanics, 124(3), 311-327.
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  Abstract: In this paper, stress and displacement fields inside a multilayered plate are analytically computed. For the theoretical modeling, individual layers of the multilayered plate are assumed to be elastic and homogeneous, but anisotropic. These theoretical computations are then experimentally verified in a qualitative manner. Experimental investigations are carried out on a ceramic composite plate that has 12 plies of fibers going in 0° and 90° directions, [0,90]3s. The incident angles and frequencies of the ultrasonic signal for generating different Lamb wave modes in this plate are obtained experimentally as well as from the theory. Displacement and stress fields inside the plate for some of these Lamb nodes are then computed. Computation of stress and displacement fields inside the plate is useful for studying the internal damage. Internal stress distribution varies significantly from one Lamb mode to another. Hence, different Lamb modes should detect defects in different layers of the plate. The Lamb mode that produces maximum stress in a specific layer should be most sensitive for detecting defects in that layer. This is observed experimentally as well.
• Yang, W., & Kundu, T. (1998). Guided waves in multilayered plates for internal defect detection. Journal of engineering mechanics, 124(3), 311--318.
• Desai, C. S., Chia, J., Kundu, T., & Prince, J. L. (1997). Thermomechanical Response of Materials and Interfaces in Electronic Packaging: Part I -Unified Constitutive Model and Calibration. Journal of Electronic Packaging, Transactions of the ASME, 119(4), 294-300.
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  Abstract: The disturbed state concept (DSC) presented here provides a unified and versatile methodology for constitutive modeling of thermomechanical response of materials and interfaces/joints in electronic chip-substrate systems. It allows for inclusion of such important features as elastic, plastic and creep strains, microcracking and degradation, strengthening, and fatigue failure. It provides the flexibility to adopt different hierarchical versions in the range of simple (e.g., elastic) to sophisticated (thermoviscoplastic with microcracking and damage), depending on the user's specific need. This paper presents the basic theory and procedures for finding parameters in the model based on laboratory test data and their values for typical solder materials. Validation of the models with respect to laboratory test behavior and different criteria for the identification of cyclic fatigue and failure, including a new criterion based on the DSC and design applications, are presented in the compendium paper (Part II, Desai et al., 1997). Based on these results, the DSC shows excellent potential for unified characterization of the stress-strain-strength and failure behavior of engineering materials in electronic packaging problems.
• Desai, C. S., Chia, J., Kundu, T., & Prince, J. L. (1997). Thermomechanical Response of Materials and Interfaces in Electronic Packaging: Part II -Unified Constitutive Models, Validation, and Design. Journal of Electronic Packaging, Transactions of the ASME, 119(4), 301-309.
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  Abstract: The constitutive modeling approach based on the disturbed state concept (DSC) described in Part I, provides a unified basis for the characterization of thermomechanical response of materials and joints in electronic chip-substrate systems. Using the material constants given in Part I, the DSC model predictions, obtained by integrating the incremental constitutive equations, are shown here to provide satisfactory backpredictions of stress-strain, fatigue, and failure responses of typical solder materials. The DSC also provides a simple criterion based on the critical disturbance to identify cyclic fatigue failure. Model predictions show good correlation with those from previous models. It is also shown how the DSC model can be used for design applications. Overall, based on Papers I and II, it can be stated that the DSC can provide a new and powerful means to characterize the thermomechanical behavior of materials and joints in a number of problems in electronic packaging.
• Desai, C. S., Chia, J., Kundu, T., & Prince, J. L. (1997). Thermomechanical response of materials and interfaces in electronic packaging: Part I—unified constitutive model and calibration. Journal of Electronic Packaging, 119(4), 294--300.
• Ghosh, T., Maslov, K. I., & Kundu, T. (1997). A new method for measuring surface acoustic wave speeds by acoustic microscopes and its application in characterizing laterally inhomogeneous materials. Ultrasonics, 35(5), 357-366.
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  Abstract: The surface acoustic wave (SAW) speed of a material is conventionally measured by an acoustic microscope from the V(z) curve (voltage V versus the defocus distance z). V(z) curves are generated by moving the lens of an acoustic microscope vertically and thus varying its distance from the specimen. Alternate constructive and destructive interferences between two rays received by the receiver produce oscillating patterns in the V(z) curves. The SAW speed is measured from the distance between two successive dips (or peaks) of the V(z) curve. Recently it has been shown that the SAW speed can also be measured from the V(f) curve. V(f) curves are generated by changing the signal frequency while the lens-specimen distance remains constant. In this paper an alternative method of measuring the SAW speed is proposed. Accuracy of different methods used to measure the SAW speed is investigated. In the new method the SAW speed is measured from the first dips of the V(z) or V(f) curves instead of the distance between two successive dips. Hence, the new methods do not need several clearly defined dips and peaks of the V(z) or V(f) curves, unlike the traditional methods. © 1997 Elsevier Science B.V.
• Jung, Y. C., Kundu, T., & Ehsani, M. (1997). Lamb wave inspection of concrete beams. American Society of Mechanical Engineers (Publication) NDE, 17, 33-46.
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  Abstract: The feasibility of detecting defects in concrete beams using Lamb waves is investigated in this paper. The traditional ultrasonic methods for inspecting defects in concrete use the reflection and scattering of longitudinal waves by internal defects. Signal amplitude and time of flight measurements provide information about the internal defects in concrete. However, these methods are time consuming and often fail to detect honeycombs, closed cracks and small defects. In this paper the potential of the Lamb wave technique to detect those defects in large concrete beams is investigated. The Lamb wave technique is found to be reliable for detecting such defects in concrete beams.
• Kundu, T. (1997). Thin film characterization by acoustic microscopy. Integrated Ferroelectrics, 15(1-4), 309-316.
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  Abstract: In this paper a brief review of the recent applications of acoustic microscopes for material property determination of thin films is given. Acoustic microscopes generate Rayleigh waves near the surface (up to one or two wave length depth) of the specimen under inspection. Since the Rayleigh wave speed is sensitive to thin film properties such as Young's modulus, Poission's ratio, longitudinal and shear wave speeds, elastic wave attenuation coefficient and density, these properties, in principle, can be extracted from the acoustic microscope generated signals. In this paper it is discussed how one can extract these properties from the V(z) curve generated by an acoustic microscope using the simplex algorithm. V(z) curve is obtained by vertically moving the microscope lens from the specimen surface, thus varying the distance (z) between the focal point of the lens and the reflecting surface of the specimen and recording the corresponding variation of the voltage (V) with z. Extraction of material properties of a thin film specimen from its V(z) curve requires solving the inversion problem, that has not been done by many investigators. The author does it by the simplex algorithm technique which is an optimization technique for solving one or more unknowns in linear or nonlinear equations. Some theoretical and experimental results involving thin (a few micron thick) metal films on a substrate and thin biological cells are also presented in this paper.
• Kundu, T., & Maslov, K. (1997). Material interface inspection by Lamb waves. INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES, 34(29), 3885-&.
• Kundu, T., & Maslov, K. (1997). Material interface inspection by Lamb waves. International Journal of Solids and Structures, 34(29), 3885-3901.
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  Abstract: In this paper an investigation on the Lamb wave propagation through a two-layered glass plate with different interface conditions between the layers is carried out to study the effectiveness of Lamb waves in detecting defects at the interface as well as estimating the interface strength. To this end the stress field inside the two layered plate is theoretically calculated for different interface conditions and for a number of propagating Lamb modes. It is observed that, for every Lamb mode, the stress field inside the plate varies significantly with depth. Symmetric modes generate maximum normal stress and zero shear stress at the central plane; the situation is reversed for the antisymmetric modes. it is found that the Lamb modes which produce large shear stress at the interface position are most sensitive to the shear stiffness of the interface. Void and delamination type defects that release the interface stress affect those Lamb modes most significantly which produce high stress at the interface position. Theoretical predictions have been experimentally verified. © 1997 Elsevier Science Ltd.
• Maslov, K., & Kundu, T. (1997). Selection of Lamb modes for detecting internal defects in composite laminates. ULTRASONICS, 35(2), 141-150.
• Maslov, K., & Kundu, T. (1997). Selection of Lamb modes for detecting internal defects in composite laminates. Ultrasonics, 35(2), 141-150.
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  Abstract: In this paper an investigation is carried out to predict the most efficient leaky Lamb mode and associated frequency to detect defects in a specific layer of a multilayered composite plate. To this end the stress and displacement fields inside a plate are theoretically calculated for different propagating leaky Lamb modes. It is observed that for every leaky Lamb mode the stress field inside the plate varies significantly with depth. A five-layer fiber reinforced composite plate with pre-existing defects, such as missing or broken fibers, and delamination is ultrasonically scanned with different leaky Lamb modes for which internal stress and displacement fields have been theoretically computed in absence of any defect. In presence of defects such as broken fibers and delamination the stresses on the defective surface are significantly reduced. Hence, if these defects are located in a region where the stress level is high for certain leaky Lamb modes then the presence of the defects will affect these modes significantly by releasing the high stress. These specific modes would then be most effective in producing the image of the defect. Theoretical predictions are then experimentally verified. © 1997 Elsevier Science B.V.
• Kundu, T., Maslov, K., Karpur, P., Matikas, T. E., & Nicolaou, P. D. (1996). A Lamb wave scanning approach for the mapping of defects in [0/90] titanium matrix composites. ULTRASONICS, 34(1), 43-49.
• Kundu, T., Maslov, K., Karpur, P., Matikas, T. E., & Nicolaou, P. D. (1996). A Lamb wave scanning approach for the mapping of defects in [0/90] titanium matrix composites. Ultrasonics, 34(1), 43-49.
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  Abstract: In this paper a new scanning technique using leaky Lamb waves is presented. This technique is applied to detect internal defects in a multilayered fiber-reinforced composite plate specimen (SCS-6 fibers in Ti-6A1-4V matrix). Images generated by this new Lamb wave scanning technique (we will refer it as the L-scan technique) are compared with conventional C-scan images. This comparison shows that the L-scan technique is more effective for detecting some internal defects such as missing fibers and fiber breakage type defects in a multilayered specimen than the conventional C-scan technique.
• Lobkis, O. I., Maslov, K. I., Kundu, T., & Zinin, P. V. (1996). Spherical inclusion characterization by the acoustic microscope: Axisymmetric case. Journal of the Acoustical Society of America, 99(1), 33-45.
• Lobkis, O. I., Maslov, K. I., Kundu, T., & Zinin, P. V. (1996). Spherical inclusion characterization by the acoustical microscope: Axisymmetric case. The Journal of the Acoustical Society of America, 99(1), 33--45.
• Maslov, K. I., Kundu, T., & Lobkis, O. I. (1996). Acoustic microscopy for spherical inclusion characterization. Journal of the Acoustical Society of America, 100(1), 80-85.
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  Abstract: In this paper a new nondestructive ultrasonic technique is developed to distinguish small spherical voids from small spherical elastic and rigid inclusions. In many materials, such as light metal casting alloys, ultrasonic scattered echoes from void-type defects and heavy metal inclusions used for strengthening purposes can give the ultrasonic signal of the same order of magnitude. It is shown in this paper how one can extract the phase information of the reflected signal to distinguish the voids from solid inclusions. When phase-frequency curves are extended to the zero frequency, then voids and solid inclusions meet at two distinct points on the phase axis separated by a distance of approximately 180°. Thus voids and solid inclusions can be clearly distinguished. Experimental results are verified by theoretical predictions.
• Maslov, K. I., Kundu, T., & Lobkis, O. I. (1996). Acoustic microscopy for spherical inclusion characterization. The Journal of the Acoustical Society of America, 100(1), 80--85.
• Awal, M. A., & Kundu, T. (1995). V (z) curve synthesis using two ultrasonic transducers. Journal of applied mechanics, 62(2), 517--522.
• Awal, M. A., & Kundu, T. (1995). V(z) curve synthesis using two ultrasonic transducers. Journal of Applied Mechanics, Transactions ASME, 62(2), 517-522.
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  Abstract: Traditionally V(z) curves are generated by acoustic microscopes. However, because of the high costs of the commercially available acoustic microscopes, their use is rather limited. In this paper it is shown how V(z) curves, which contain quantitative information about the material under inspection, can be generated using two ultrasonic transducers instead of an acoustic microscope. A theoretical analysis is given to synthesize V(z) curves of orthotropic plates by this technique. A basic mechanics problem of the reflection of plane waves by an orthotropic plate immersed in a fluid is solved for this purpose. Theoretically synthesized V(z) values are compared with experimental results.
• Basaran, C., Desai, C. S., Kundu, T., & Prince, J. (1995). Computer simulation of the temperature cycling tests. American Society of Mechanical Engineers, EEP, 12, 77-82.
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  Abstract: Temperature cycling tests are used to determine the number of cycles to failure of the solder joints in the surface mount technology packages. In this paper the thermomechanical fatigue of Pb40/Sn60 solder joint in a leadless ceramic chip carrier package is studied and Hall [1984] temperature cycling test is simulated by using a finite element procedure with the Disturbed State Concept (DSC) constitutive models. The progress of disturbance (damage) and the energy dissipated in the solder joint during thermal cycling are predicted. It is shown that the disturbance criterion used follows a similar path as the energy dissipation in the system. Moreover, the comparisons between the test data and the finite element analysis show that the number of cycles to failure of a solder joint can be accurately predicted by a finite element procedure using the DSC material models. Furthermore, the analysis give a good picture of the progress of the failure mechanism and the disturbance in the solder joint.
• Desai, C. S., Jagannath, S. V., & Kundu, T. (1995). Mechanical and ultrasonic anisotropic response of soil. Journal of Engineering mechanics - ASCE, 121(6), 744-752.
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  Abstract: This paper describes experimental procedures to relate multiaxial mechanical and ultrasonic responses of a cemented sand toward a study of stress-induced anisotropy due to microstructural changes under loading, unloading, and reloading. It is shown that the ultrasonic velocities and attenuation can provide indirect measures of microcracking and resulting induced anisotropy. -from Authors
• Desai, C. S., Jagannath, S. V., & Kundu, T. (1995). Mechanical and ultrasonic anisotropic response of soil. Journal of engineering mechanics, 121(6), 744--752.
• Desai, C., Kundu, T., & Prince, J. (1995). COMPUTER SIMULATION OF THE TEMPERATURE CYCLING TESTS. Structural Analysis in Microelectronics and Fiber Optic Systems, 77.
• Karpur, P., Benson, D. M., Matikas, T. E., Kundu, T., & Nicolaou, P. D. (1995). Approach to determine the experimental transmitter-receiver geometry for the reception of leaky Lamb waves. Materials Evaluation, 53(12), 1348-1352.
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  Abstract: Often, either the swept frequency technique or a combination of swept frequency and geometric analysis is used to produce the experimental Lamb wave dispersion data. This paper describes an approach for constructing dispersion curves in solid plates using Fourier analysis of received leaky Lamb wave signals. The Lamb waves are produced by pulsed ultrasound generated using two broad band transducers positioned in a pitch-catch orientation. The relative distances among the plate and the two transducers are set to specific values as per geometric calculations based on beam diffraction. The transducer defocus is used in conjunction with geometric calculation to determine the phase velocity of the Lamb wave mode being monitored. Subsequent to appropriate positioning of the transducers, the plate wave signals are Fourier transformed to obtain a magnitude versus frequency spectrum. Peaks in the spectrum indicate the presence of a Lamb wave root. The feasibility of this method, tested by successfully constructing dispersion curves for a steel plate, is compared with the `null zone' monitoring method of generation of the dispersion curves. The geometric positioning method is further applied to a metal matrix composite sample wherein the sensitivity of various experimentally generated Lamb wave modes is assessed to detect many types of preprogrammed defects in different layers of the composite plate.
• Kundu, T. (1995). Inverse problems in enginneering mechanics. HD Bui, M. Tanaka, M. Bonnet, H. Maigre, E. Luzzato and M. Reynier (Editors), ISBN 90 54015178, Price US $110, 474 pages. International Journal for Numerical and Analytical Methods in Geomechanics, 19(8), 582--582.
• Lobkis, O. I., Kundu, T., & Zinin, P. V. (1995). A theoretical analysis of acoustic microscopy of spherical cavities. Wave Motion, 21(2), 183-201.
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  Abstract: In this paper a theoretical analysis of acoustic microscopy of spherical cavities in solids is presented. The incident field of the acoustic microscope is modeled as a converging acoustic beam of nonplanar wave front. This beam goes through reflection and transmission at the liquid-solid interface. The transmitted beam is scattered by the spherical cavity in solid. The scattered waves come back to the receiver after going through another transmission at the liquid-solid interface. Voltage curves generated by this signal for small as well as large cavities in different materials are analytically synthesized for both horizontal and vertical movements of the microscope lens. It is also shown in this paper how one can obtain the size and location of a cavity from the acoustic microscope generated voltage curves. © 1995.
• Lobkis, O. I., Maslov, K. I., & Kundu, T. (1995). University of Arizona, Tucson, AZ 85721, USA PV Zinin. Review of Progress in Quantitative Nondestructive Evaluation, 14, 123.
• Maslov, K. I., Zinin, P. V., Lobkis, O. I., & Kundu, T. (1995). V(Z) curve formation of solid spherical microparticles in scanning acoustic microscopy. Journal of Microscopy, 178(2), 125-133.
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  Abstract: Information about the properties of materials in acoustic microscopy can be obtained in the form of the V(Z) curves. The purpose of this paper is to present the theoretical and experimental study of the V(Z) curve formation for solid spheres. It is shown that an investigation of the position of different peaks in the V(Z) curves is useful to determine the size and acoustical properties of a spherical particle.
• Xu, L., & Kundu, T. (1995). Stress singularities at crack corners. Journal of Elasticity, 39(1), 1-16.
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  Abstract: In this paper the stress and displacement fields near an embedded crack corner in a linear elastic medium are analytically computed. The conical-spherical coordinate system is introduced to solve this problem. It is observed that the strength of the stress singularity depends on the angle of the crack corner. The singularity becomes weaker, varying from r-1 to r0, as the angle of the crack corner varies from 360° to 0°. Both symmetric and skew-symmetric loadings give the same variation of the behavior of the stress singularity. It is also found that the order of the singularity is independent of the Poisson's ratio, unlike the corner cracks at a free surface where Poisson's ratio affects the results.
• Xu, L., & Kundu, T. (1995). Stress singularities at crack corners. Journal of elasticity, 39(1), 1--16.
• Kundu, T. (1994). Nondestructive testing techniques and their applications. Computer Meth Geom, 1, 171.
• Kundu, T., & Blodgett, M. (1994). Detection of material defects in layered solids using Lamb waves. Review of Progress in Quantitative Nondestructive Evaluation, 13, 1343--1343.
• Kundu, T., & Maxfield, B. (1994). Erratum: A new technique for measuring Rayleigh and lamb wave speeds (Journal of the Acoustical Society of America (1993) 93 (3066)). Journal of the Acoustical Society of America, 95(1), 566-.
• Kundu, T., & Maxfield, B. (1994). Erratum:‘‘A new technique for measuring Rayleigh and Lamb wave speeds’’[J. Acoust. Soc. Am. 93, 3066 (1993)]. The Journal of the Acoustical Society of America, 95(1), 566--566.
• Romanel, C., & Kundu, T. (1994). A hybrid method for dynamic soil-structure interaction. Applications of computational mechanics in geotechnical engineering. Proc. workshop, Rio de Janeiro, 1991, 439-452.
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  Abstract: A hybrid method is proposed in this paper for dynamic soil-structure interaction analysis of embedded structures within a multilayered elastic half-space. A near field region, containing the structure and a portion of soil surrounding it, is modeled by finite elements while the far field formulation is obtained through the classical wave propagation theory based on the assumption that the actual scattered wave fields can be represented by a set of line sources located at a depth corresponding to the center of mass of the structure under investigation. Traction reciprocity between the two regions is satisfied exactly while the displacement continuity across the common interface is enforced in a least-squares sense. The two-dimensional system is excited by seismic body waves (P and SV) propagating with oblique incidence and harmonic time dependence. -Authors
• Yang, W., & Kundu, T. (1994). Efficient use of lamb waves to characterize multilayered anisotropic plates. American Society of Mechanical Engineers, Applied Mechanics Division, AMD, 188, 109-120.
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  Abstract: In this paper the use of Lamb waves to characterize multilayered anisotropic plates is investigated. Individual layers in the multilayered specimen are elastic, homogeneous and anisotropic. The incident angle and frequency of an ultrasonic signal for the Lamb wave generation in a multilayered composite plate are first obtained. Displacement and stress fields inside the plate associated with different Lamb wave modes are computed for a number of orientations of a two layered fiber reinforced composite plate. It shows that for detecting and imaging defects in a specific layer certain Lamb wave modes are more effective than others. Preliminary results also indicate that Lamb waves are more efficient for characterizing composite plates made of anisotropic layers rather than isotropic layers.
• Chia, J. H., Desai, C. S., Kundu, T., Basaran, C., & Prince, J. L. (1993). Unified constitutive modelling of interfaces and materials in semiconductor devices. American Society of Mechanical Engineers, EEP, 7, 113-119.
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  Abstract: A unified constitutive modelling approach is developed based on the disturbed state concept (DSC) with the hierarchical single surface plasticity (HiSS) based models. With this approach, various factors such as plastic and creep strains effects, and damage due to microcracking and fracture are considered as disturbances, and incorporated in a basic reference model in a progressive manner. As a result, the approach provides flexibility to adopt various versions of the model depending on the need of users. The thermoplastic model, δθ, presented here describes hardening response of materials/interfaces during monotonic as well as cyclic thermomechanical loads. In addition to the thermoplastic model, a thermoviscoplastic model, δθv, presented here was used to simulate creep and stress relaxation mechanisms at elevated temperatures; here the rate effect on the hysteretic response is incorporated in the incremental constitutive equations. This model can allow for any stress-strain history and can be used for investigation of the time dependence of low-cycle fatigue life prediction of solder materials. The temperature dependence of material constants are found using available laboratory tests, and is represented by using simple power functions. These models have the merit of being relatively simple, and they can be readily adapted in nonlinear finite element codes. Preliminary verification of the above two versions of model is obtained for solder materials in semiconductor devices.
• Kundu, T. (1993). Introduction to finite and boundary element methods for engineers (G. Beer and JO Watson, Wiley, New York, 1992. ISBN 0471 928135 522 pp.). International Journal for Numerical and Analytical Methods in Geomechanics, 17(8), 600--600.
• Kundu, T., & Maxfield, B. (1993). A new technique for measuring Rayleigh and Lamb wave speeds. Journal of the Acoustical Society of America, 93(6), 3066-3073.
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  Abstract: A new technique is proposed in this paper to measure Rayleigh and Lamb wave speeds in solid half-spaces and plates. In this technique two transducers are positioned above the specimen in a pitch-catch orientation. The time of flight of the signal from the transmitter to the receiver is recorded. Then the rate of change of this time as the distance between the reflector and the transducer varies is experimentally determined. This rate remains constant when leaky Rayleigh of Lamb waves are generated but it varies when these waves are not generated. Thus surface waves are detected in an indirect manner. An expression is derived to relate the surface wave speed to the signal flight time change rate with the transducer specimen distance. Using this expression Rayleigh and Lamb wave speeds have been accurately determined in isotropic metals and anisotropic composites.
• Romanel, C., & Kundu, T. (1993). A hybrid modelling of soil--structure interaction problems for deeply embedded structures in A multilayered medium. Earthquake engineering & structural dynamics, 22(7), 557--571.
• Romanel, C., & Kundu, T. (1993). Analysis of deeply embedded structures in a layered half-space. Proceedings of the International Conference on Offshore Mechanics and Arctic Engineering - OMAE, 1, 379-386.
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  Abstract: A hybrid method is proposed in this paper for dynamic soil-structure interaction analysis of embedded structures within a multilayered elastic half-space. A near field region, containing the structure and a portion of soil surrounding it, is modeled by finite elements while the far field formulation is obtained through the classical wave propagation theory based on the assumption that the actual scattered wave fields can be represented by a set of line sources located at a depth corresponding to the center of mass of the structure under investigation. Traction reciprocity between the two regions is satisfied exactly while the displacement continuity across the common interface is enforced in a least-squares sense. The two-dimensional system is excited by seismic body waves (P and SV) propagating with oblique incidence and harmonic time dependence.
• Romanel, C., & Kundu, T. (1993). Hybrid modelling of soil-structure interaction problems for deeply embedded structures in a multilayered medium. Earthquake Engineering and Structural Dynamics, 22(7), 557-571.
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  Abstract: Dynamic response of deeply embedded structures, such as underground tunnels and deep foundations, in a multilayered elastic half-space are analyzed when the structure is excited by a plane P or SV wave propagating at some angle. The scattered field is represented by the sum of three Green's functions, corresponding to two oscillating forces and one oscillating moment at the centroid position of the buried structure. The amplitudes of these two forces and one moment are a priori unknown and are obtained by satisfying displacement and stress continuity conditions across the near-field/far-field boundary. The distinguishing feature of this technique from direct or indirect boundary integral techniques is that in these techniques a distribution of sources of unknown amplitude are considered at the near-field/far-field boundary, and a large number of sources are needed for different combinations of source-receiver arrangements. But in this technique the sources of unknown amplitude are placed at the location of the structure, not at the near-field/far-field boundary and, using the Saint Venant's principle, the scattered field is modelled. Thus, the number of sources required is reduced to only three. Two example problems are solved. The first one is for a deeply embedded footing in a three-layer soil mass and the second one is for a rectangular tunnel in a two-layer soil mass.
• Awal, M. A., Mahalanobis, A., & Kundu, T. (1992). Low frequency acoustic microscopy and pattern recognition for studying damaged and anisotropic composites and material defects. Journal of Nondestructive Evaluation, 11(1), 19-28.
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  Abstract: In recent years, acoustic microscopy has been found to be very useful for characterizing engineering as well as biologic materials. With the present state of knowledge on acoustic microscopy, one can obtain the surface wave velocity of a homogeneous specimen or coating thickness of a coated material and produce images of near surface internal defects and inhomogeneities in a specimen. Applications of acoustic microscopy for obtaining material properties of anisotropic specimens and detecting material defects at a greater depth are meager because commercially available acoustic microscopes are insensitive to direction-dependent material properties and they, in general, have poor penetration properties because of high operating frequencies. Recently at the University of Arizona an unconventional low frequency (0.5-2.5 MHz) acoustic microscope has been fabricated where the microscope lens has been replaced by two ultrasonic transducers with cylindrical concave faces; one works as a transmitter and the other one works as a receiver. Using this arrangement, it has been found that it is possible to detect internal damages in a material and identify material anisotropy in fiber-reinforced composite plates. These capabilities of the microscope are demonstrated in this paper by presenting some experimental results along with theoretical justifications. Then pattern recognition techniques are used to solve the inverse problem, that is, to predict the type of material defect from reflected acoustic signals. © 1992 Plenum Publishing Corporation.
• Awal, M. A., Mahalanobis, A., & Kundu, T. (1992). Low frequency acoustic microscopy and pattern recognition for studying damaged and anisotropic composites and material defects. Journal of nondestructive evaluation, 11(1), 19--28.
• Bereiter-Hahn, J., Berghofer, F., Kundu, T., Penzkofer, C., & Hillmann, K. (1992). Evaluation of mechanical properties of cells by scanning acoustic microscopy using V(z) characteristics. American Society of Mechanical Engineers, Applied Mechanics Division, AMD, 140, 71-80.
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  Abstract: Taking advantage of the deviation of the glass V(z) characteristics induced by a thin layer of cytoplasm on top of a plane glass surface we calculated the P-wave velocity, attenuation, thickness of the cytoplasmic layer, and density for a fixed endothelial cell in culture. For the first time the calculations were done for the full projection surface of a cell within the lateral resolution of the scanning acoustic microscope operated at 1 GHz (ca. 0.8 μm). Thus a 2-dimensional image of the stiffness distribution of a single cell was obtained at this resolution. The thickness values obtained were compared with the surface topography revealed by a light microscopic method (reflection interference microscopy) and gave good coincidence of the values. The coincidence of the thickness values achieved by two independent methods are in favor of the reliability of the parameters calculated from the acoustic images. High P-wave velocities appear in some F-actin accumulations.
• Jagannath, S. V., Desai, C. S., & Kundu, T. (1992). Fracture processes. Geotech Test J, 15, P138--157.
• KARIM, M. R., AWAL, M. A., & KUNDU, T. (1992). ELASTIC WAVE SCATTERING BY CRACKS AND INCLUSIONS IN PLATES - INPLANE CASE. INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES, 29(19), 2355-2367.
• Karim, M. R., Awal, M. A., & Kundu, T. (1992). Elastic wave scattering by cracks and inclusions in plates: In-plane case. International Journal of Solids and Structures, 29(19), 2355-2367.
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  Abstract: The scattering of elastic waves in a plate by a distribution of inclusions and/or cracks within a finite zone is studied by a combination of analytical and finite element methods. The incident field is generated by either a time harmonic beam of finite width or guided waves. A part of the plate containing the inclusions/cracks (interior region) is modeled by conventional finite elements. The far-field (exterior region) is approximated by a number of guided (Lamb) wave modes with real wave numbers. The scattered and total fields (displacements and stresses) are obtained by matching the two regions to satisfy the displacement and stress compatibilities at the near field-far field boundary. Numerical results are presented showing the effects of cracks and inclusions in a plate. © 1992.
• Karim, M. R., Awal, M. A., & Kundu, T. (1992). Numerical analysis of guided wave scattering by multiple cracks in plates: SH-case. Engineering Fracture Mechanics, 42(2), 371-380.
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  Abstract: A hybrid finite element method is proposed for the analysis of guided wave scattering in a plate containing multiple subsurface cracks at arbitrary orientations. A part of the plate around the cracks (interior region) is modeled by conventional finite elements. The far-field (exterior region) is approximated by a finite number of guided wave modes. Matching at the interface between the two regions is obtained by satisfying the stress and displacement compatibility conditions. Numerical results showing the effects of cracks in a plate, in the form of changes in spectra and pulse shapes of the displacements on the surface of the plate, are presented. © 1992.
• Karim, M. R., Awal, M. A., & Kundu, T. (1992). Numerical analysis of guided wave scattering by multiple cracks in plates: SH-case. Engineering fracture mechanics, 42(2), 371--380.
• Kundu, T. (1992). A complete acoustic microscopical analysis of multilayered specimens. Journal of applied mechanics, 59(1), 54--60.
• Kundu, T. (1992). Complete acoustic microscopical analysis of multilayered specimens. Journal of Applied Mechanics, Transactions ASME, 59(1), 54-60.
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  Abstract: A theoretical analysis is carried out to synthesize the V(z) curves of multilayered solids immersed in water. Solid layers attenuate ultrasound and change its phase. A liquid layer may be located in between two solid layers. The goal of this analysis is to avoid the three major simplifying assumptions of the presently available techniques, as paraxial approximation, assumption of perfect reflection and ambiguous pupil function or incident field strenght variation in the illuminated region. Presently available techniques developed for conventional acoustic microscopes can avoid some but not all of these assumptions for computing the V(z) curve. In this paper, the analysis is carried out for a spherical cavity lens with a large aperture angle. The V(z) curve for a uniform glass half-space is synthesized analytically and compared with experimental results. Analytical results are also presented for chromium plated glass specimens and biological cells on uniform glass half-space. Such an exact analysis of multilayered specimens is necessary for material science research as well as cell research in biology, because advanced engineering composite materials and biological cells in culture have multiple layers.
• Kundu, T. (1992). Computational aspects of contact, impact and penetration: RF Kulak and LE Schwer (editors) Elmpress International, Switzerland, 1991, 312 pages, ISBN 2-9400941-5. International Journal for Numerical and Analytical Methods in Geomechanics, 16(6), 461--461.
• Kundu, T. (1992). Inversion of acoustic material signature of layered solids. Journal of the Acoustical Society of America, 91(2), 591-600.
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  Abstract: The simplex inversion technique is applied to the acoustic material signature (AMS) of layered solids to obtain thickness and material properties of layers. It is shown in this paper that by careful application of the simplex technique, it is possible to extract much information about a multilayered specimen from its AMS. A brief review of different inversion techniques is also given in the paper from which the relative advantages of using the simplex algorithm over other techniques are derived.
• Kundu, T., & Bostr"om, A. (1992). Elastic wave scattering by a circular crack in a transversely isotropic solid. Wave Motion, 15(3), 285--300.
• Kundu, T., & Boström, A. (1992). Elastic wave scattering by a circular crack in a transversely isotropic solid. Wave Motion, 15(3), 285-300.
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  Abstract: The scattering of arbitrary elastic waves by a circular crack in a tranversely isotropic solid is investigated. The symmetry axis of the solid and the normal to the crack are parallel. The problem is first divided into a symmetric and an antisymmetric part with respect to the plane of the crack. A Fourier-Hankel representation for the scattered field is then assumed and some manipulations using the conditions in the plane of the crack lead to an integral equation for the normal crack opening displacement for the symmetric part and two coupled integral equations for the tangential components of the crack opening displacement for the antisymmetric part. The crack opening displacements are expanded in series of Legendre functions which fulfil the correct edge conditions and the integral equations are projected on the same set of Legendre functions. The far field is calculated with the stationary phase method. Numerical results are given for crack opening displacements for incident quasi P and SV plane waves and compared with corresponding results for an isotropic solid. © 1992.
• Kundu, T., & Maxfield, B. (1992). New technique to detect surface waves and measure their velocities. American Society of Mechanical Engineers, Applied Mechanics Division, AMD, 140, 81-98.
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  Abstract: A low frequency (0.5 - 2.5 Mhz) acoustic microscope is used to generate and detect surface waves in isotropic and anisotropic solids. In this microscope one transducer with a cylindrical concave front face produces a line focused ultrasonic beam which strikes the specimen at any desired angle. The reflected beam is received by another transducer. When the incident angle of the striking beam becomes equal to the critical angle of the reflector, surface waves are generated otherwise the beam is specularly reflected without generating any surface wave. It is shown in this paper that by measuring the change in the arrival time as the distance between the reflecting surface and the transducer changes one can predict if the surface waves have been generated or not. Experiments are carried out with copper and aluminum blocks and graphite-epoxy (graphite fibers in epoxy matrix) composite plate. It is found that it is easier to generate and detect surface waves in isotropic metallic blocks where Rayleigh waves are nondispersive than anisotropic graphite epoxy composite plate where Lamb waves are dispersive.
• Kundu, T., Bereiter-Hahn, J., & Hillmann, K. (1992). Calculating acoustical properties of cells: Influence of surface topography and liquid layer between cell and substrate. Journal of the Acoustical Society of America, 91(5), 3008-3017.
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  PMID: 1629492;Abstract: In this paper, a mathematical formulation is presented to compute the V(z) of a tapering layered solid and applying this formulation to the determination of acoustic properties of biological cells and tissues. The formulation is adopted in the simplex inversion algorithm to obtain the acoustic properties of a tapering cell from its V(z) values. The influence of two parameters had been considered: The tapering angle and the presence of a thin liquid layer present between cells and the substratum to which they adhere. Up to a tapering angle less than 10°, it can be safely neglected. However, if a larger angle is neglected, then the acoustic wave velocity in the cell is overestimated. Cell thickness estimation is not affected significantly when the tapering angle is ignored. The calculations of acoustic properties of cells are considerably influenced by the introduction of a thin fluid layer between the solid substratum and the overlying cell, neglecting the presence of at least a very thin layer (20-30 nm), in general, results in a considerable overestimation of sound velocity. The reliability of the data calculated from V(z) values was ascertained using an independent method to determine cell thickness by calculating it from the interference fringe pattern obtained with the reflection-interference light microscope. The shape of the glutaraldehyde-fixed cells was similar to fried eggs. The highest sound velocities were found close to the periphery of the dome-shaped cell center. In the very center and over most of the area of the thin periphery, sound velocity was close to that in saline.
• Awal, M. A., & Kundu, T. (1991). Material characterization of composites by acoustic microscopy. American Society of Mechanical Engineers (Publication) NDE, 10, 1-7.
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  Abstract: In recent years, acoustic microscopy has been found to be very useful for characterizing engineering as well as biologic materials. With the present state of knowledge on acoustic microscopy, one can obtain the surface wave velocity of a homogeneous specimen or coating thickness of a coated material and produce images of near surface internal defects and inhomogeneities in a specimen. Applications of acoustic microscopy for obtaining material properties of anisotropic specimens and detecting material defects at a greater depth are meager because commercially available acoustic microscopes are insensitive to direction dependent material properties and they, in general, have poor penetration properties because they operate at high frequencies. Recently at the University of Arizona an unconventional low frequency (0.5-2.5 MHz) acoustic microscope has been fabricated where the microscope lens has been replaced by two ultrasonic transducers with cylindrical concave faces; one works as a transmitter and the other one works as a receiver. Using this arrangement it has been found that it is possible to detect internal damages in a material and identify material anisotropy in fiber reinforced composite plates. These capabilities of the microscope are demonstrated in this paper by presenting some experimental results. It can also generate AMS or V(z) curves of any specimen. V(z) curves of isotropic and orthotropic plates are analytically synthesized in this paper and experimental results are compared with analytically synthesized curves.
• Jagannath, S. V., Desai, C. S., & Kundu, T. (1991). Measurements of material anisotropy by ultrasonic technique. Soil Dynamics and Earthquake Engineering V, 223-234.
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  Abstract: Many geologic materials when subjected to sequences of loading, unloading and re-loading, experiences induced anisotropy, due to factors such as microstructural changes and damage. Herein, an experimental procedure has been developed, which enables multi-axial mechanical (destructive) and ultrasonic (non-destructive) testing of geologic materials. The paper describes the experimental scheme, data acquisition system and test results on a cemented sand under hydrostatic stress path of loading, unloading and re-loading. Examination of the stress-strain, stress-velocity and stress-attenuation data provides insight into the material anisotropy, its quantification, and correlation between mechanically defined anisotropy and non-destructively measured anisotropy.
• KUNDU, T., BEREITERHAHN, J., & HILLMANN, K. (1991). MEASURING ELASTIC PROPERTIES OF CELLS BY EVALUATION OF SCANNING ACOUSTIC MICROSCOPY V(Z) VALUES USING SIMPLEX ALGORITHM. BIOPHYSICAL JOURNAL, 59(6), 1194-1207.
• Karim, M. R., & Kundu, T. (1991). Dynamic response of an orthotropic half-space with a subsurface crack. In-plane case. Journal of Applied Mechanics, Transactions ASME, 58(4), 988-995.
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  Abstract: Scattering of elastic waves by a subsurface crack in an orthotropic half-space subjected to a surface line load of arbitrary angle of inclination is studied. Green's functions are developed and used along with the representation theorem to reduce the problem to a set of simultaneous singular integral equations in the Fourier transformed domain. Solution to these equations is then obtained by expanding the unknown crack opening displacement (COD) in terms of Chebyshev polynomials. Numerical results are given for specific examples involving orthotropic materials.
• Kundu, T. (1991). Dynamic Response of an Orthotopic Half-Space With a Subsurface Crack: In-Plane Case.
• Kundu, T., & Bostroem, A. (1991). Axisymmetric scattering of a plane longitudinal wave by a circular crack in a transversely isotropic solid. Journal of Applied Mechanics, Transactions ASME, 58(3), 695-702.
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  Abstract: The scattering of elastic waves by a circular crack situated in a transversely isotropic solid is studied here. The axis of material symmetry and the axis of the crack coincides. The incident wave is taken as a plane longitudinal wave propagating perpendiculr to the crack surface. A Hankel transform representation of the scattered field is used, and after some manipulations using the boundary conditions this leads to an integral equation over the crack for the displacement jump across the crack. This jump is expanded in a series of Legendre polynomials which fulfill the correct edge condition and the integral equation is projected on the same set of Legendre polynomials. The far field is computed by the stationary phase method. A few numerical computations are carried out for both isotropic and anisotropic solids. Results for the isotropic solid compare favorably with those available in the literature.
• Kundu, T., & Bostrom, A. (1991). Axisymmetric scattering of a plane longitudinal wave by a circular crack in a transversely isotropic solid. Journal of applied mechanics, 58(3), 695--702.
• Kundu, T., Bereiter-Hahn, J., & Hillmann, K. (1991). Measuring elastic properties of cells by evaluation of scanning acoustic microscopy V(z) values using simplex algorithm. Biophysical Journal, 59(6), 1194-1207.
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  PMID: 19431793;PMCID: PMC1281200;Abstract: In this paper a new technique is proposed to determine the acoustic properties as well as the thickness (and volume) of biological cells. Variations of thickness, density, acoustic wave velocity, stiffness, and attenuation coefficient of a living or dead cell are obtained by scanning the cell by an acoustic microscope. The distance between the cell and the microscope lens is varied and several voltage curves are thus obtained. These curves are then inverted by simplex optimization technique to obtain the cell parameters. The spatial resolution of the method is limited to the resolution of the scanning acoustic microscope. It allows to take advantage of the full range of frequencies and amplification of the microscope. Characteristic distributions of stiffness are exemplified with an endothelial cell in culture. The main part of the thin, lamellar cytoplasm has high stiffness, which drops close to the lamella/cell body transition region and only slightly increases again through the central part of the cell. Acoustic attenuation seems to be related to two factors, cytoplasm accumulation (in the lamellar parts) and scattering in the central part rich in organelles.
• Kundu, T., Mathur, R. P., & Desai, C. S. (1991). Three dimensional soil-structure interaction analysis. Deformable structures in multilayered soil mass. Engineering computations, 8(2), 153-180.
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  Abstract: A new hybrid method based on three-dimensional finite element idealization in the near field and a semi-analytic scheme using the principles of wave propagation in multilayered half space in the far field is proposed for the dynamic soil-structure interaction analysis. The distinguishing feature of this technique from direct or indirect boundary integral techniques is that in boundary integral techniques a distribution of sources are considered at the near field boundary. Strengths of these sources are then adjusted to satisfy the continuity conditions across the near-field/far-field interface. In the proposed method unknown sources are placed not at the near field boundary but at the location of the structure. Then the Saint-Venant's principle is utilized to justify that at a distant point the effect of the structure's vibration can be effectively modelled by an equivalent vibrating point force and vibrating moment at the structure's position. Thus the number of unknowns can be greatly reduced here. For soil-structure interaction analysis by this method one needs to consider only three unknowns (two force components and one in-plane moment) for a general two-dimensional problem and six unknowns (three force components and three moment components) for a general three-dimensional problem. When a vertically propagating elastic wave strikes a structure which is symmetric about two mutually perpendicular vertical planes the structure can only vibrate vertically for dilatational waves and horizontally for shear waves. Under this situation the number of unknowns is reduced to only one whereas in boundary integral and boundary element techniques the number of unknowns is dependent on the number of nodes at the near field boundary, which is generally much greater than six. Several example problems are solved in this paper using this technique for both flexible and rigid structures in multilayered soil media.
• Romanel, C., & Kundu, T. (1991). A Hybrid Modeling of Soil Structure Interaction Problems.
• Desai, C. S., Kundu, T., & Wang, G. (1990). Size effect on damage parameters for softening in simulated rock. International Journal for Numerical and Analytical Methods in Geomechanics, 14(7), 509-517.
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  Abstract: Laboratory uniaxial tests on cylindrical specimens of a simulated rock are used to identify the influence of the diameter (D) and height (L) of the specimens on the damage parameters. The relations are expressed in terms of the characteristic parameter C = L2/D.
• Karim, M. R., & Kundu, T. (1990). Scattering of acoustic beams by cracked composites. Journal of Engineering Mechanics, 116(8), 1812--1827.
• Karim, R., & Kundu, T. (1990). Scattering of acoustic beams by cracked composites. Journal of Engineering Mechanics, 116(8), 1812-1827.
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  Abstract: The scattering of elastic waves by a subsurface crack in a fiber-reinforced composite half-space immersed in a liquid is analytically studied in this paper. The composite half-space is subjected to a bounded acoustic beam, propagating at an arbitrary angle of inclination. To solve this problem, two new Green's functions are developed for unit loads acting in horizontal and vertical directions in a flawless submerged orthotropic half-space. The governing equations along with boundary, regularity, and interface conditions are reduced to a coupled set of singular integral equations in terms of the unknown crack opening displacement (COD) by using representation theorem along with Green's function. The solution of these equations is obtained by expanding the unknown COD in terms of Chebychev polynomials. The problem is first solved in the frequency domain. Time histories are then obtained by using fast Fourier transform (FFT) routines.
• Kundu, T. (1990). Scattering of torsional waves by a circular crack in a transversely isotropic solid. Journal of the Acoustical Society of America, 88(4), 1975-1980.
• Romanel, C., & Kundu, T. (1990). Soil-structure interaction in a layered medium. International Journal of Engineering Science, 28(3), 191-213.
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  Abstract: A hybrid method based on the Green's function formalism is proposed for two-dimensional dynamic soil-structure interaction analysis in a multilayered half-space. The method models the near field (structure and surrounding soil) by finite elements and solves the far field problem through a continuum approach based on an adaptation of the Thomson-Haskell matrix formulation. Displacement continuity between the two regions is enforced by least-squares error minimization. The whole system is excited by steady plane waves (P and SV) propagating with oblique incidence and the structure can be assumed either on the surface or embedded at shallow depth. Special consideration of the scattered field permits the discretized region to be kept reasonably small. © 1990.
• Romanel, C., & Kundu, T. (1990). Soil-structure interaction in a layered medium. International journal of engineering science, 28(3), 191--213.
• Awal, M. A., Kundu, T., & Joshi, S. P. (1989). Dynamic behavior of delamination and transverse cracks in fiber reinforced laminated composites. Engineering Fracture Mechanics, 33(5), 753-764.
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  Abstract: In this paper a numerical method is developed to study the dynamic behavior of delamination and transverse cracks in lamianted fiber-reinforced composite plates of finite dimension. The plate is subjected to time dependent antiplane shear stress field which is acting on the plate surfaces. The interaction of waves diffracted at the crack tip with those reflected at the plate boundaries and transmitted at the material interface makes the problem very complicated, so analytical study of this problem cannot be carried out with our present state of knowledge. Hence the problem is solved numerically. A versatile functional is developed which can handle delamination and transverse cracks with any orientation in multilayered composite laminates. The variational principle is adopted in frequency domain to obtain the finite element equations. The numerical difficulty associated with the singular behavior of the stress field near the crack tip has been avoided by using quarter point elements. © 1989.
• Awal, M. A., Kundu, T., & Joshi, S. P. (1989). Dynamic behavior of delamination and transverse cracks in fiber reinforced laminated composites. Engineering fracture mechanics, 33(5), 753--764.
• Karim, M. R., & Kundu, T. (1989). Transient response of three layered composites with two interface cracks due to a line load. Acta mechanica, 76(1-2), 53--72.
• Karim, M. R., Kundu, T., & Desai, C. S. (1989). Detection of delamination cracks in layered fiber-reinforced composite plates. Journal of Pressure Vessel Technology, Transactions of the ASME, 111(2), 165-171.
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  Abstract: In this paper, the dynamic response of delamination cracks in a layered fiber-reinforced composite plate is analytically studied. The plate is subjected to an antiplane loading and its surface response is computed in absence as well as in presence of delamination cracks. To what extent the surface response is influenced by the presence of internal delamination cracks is investigated here. This study is important for nondestructive evaluation of internal damage in composites due to delamination. The problem is formulated in terms of integral equations in frequency domain. These equations are then solved by expanding the unknown crack opening displacement in a complete set of Chebychev's polynomials, whose coefficients are solved by satisfying the traction-free condition at the crack surface.
• Karim, M., & Kundu, T. (1989). Transient response of three layered composites with two interface cracks due to a line load. Acta Mechanica, 76(1-2), 53-72.
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  Abstract: The dynamic response of three layered composites, with two interface cracks, subjected to an antiplane line load is analyzed. The Green's function for the uncreacked medium is used along with the representation theorem to derive the scattered field. Satisfaction of the traction free condition at the crack surfaces gives rise to a system of singular integral equations for determining crack opening displacements (COD), which are then solved by expanding the unknown COD in a complete set of Chebyshev polynomials. Numerical results for two sample problems are presented, for both isotropic and anisotropic materials. Results show how significantly material anisotropy and interaction between two cracks can affect the COD in a three layered plate. © 1989 Springer-Verlag.
• Kundu, T., & Desai, G. S. (1989). Detection of delamination cracks in layered fiber-reinforced composite plates. Journal of pressure vessel technology, 111, 165.
• Desai, C. S., Kundu, T., & Wang, G. (1988). Effect of specimen size on progressive damage and softening in simulated rock. American Society of Mechanical Engineers, Petroleum Division (Publication) PD, 26, 161-163.
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  Abstract: It has been shown previously that the damage accumulation and resulting strain-softening behavior of geologic materials can be modelled by introducing a damage parameter, r, in the hierarchical approach of constitutive modelling. This parameter r, which is a function of deviatoric plastic strain trajectory, varies from zero for no damage condition to unity for maximum damage. Effects of sample size such as diameter and height in laboratory tests on the value of r have not been fully understood. In this paper, the effect of the height of the specimen on the damage parameter is investigated. Attention is restricted to laboratory tests with cylindrical specimens in which the specimen diameter D = 3.0 inch (7.62 cm) is maintained constant, while its height is varied. Since it is difficult to carry out this experimental investigation on real rocks, a rock-like material is simulated from a mixture of plaster of paris, cement, sand and water.
• Karim, M. R., & Kundu, T. (1988). Acoustic material signature of fiber reinforced composites. American Society of Mechanical Engineers, Petroleum Division (Publication) PD, 24, 131-134.
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  Abstract: Potential use of acoustic microscopy at low frequency for determining elastic properties and characterizing internal defects have been recognized in the recent years. In this paper a theory is presented for the calculation of the acoustic material signature of an orthotropic half-space overlain by a fluid. The analysis is carried out for low frequency acoustic waves generated by a cylindrical transducer without a lens rod and the response is measured by a line receiver. Several new features of the material signature and their possible use in fiber reinforced composite material characterization are indicated.
• Karim, M. R., & Kundu, T. (1988). Detection of delamination cracks in layered fibre reinforced composite plates. American Society of Mechanical Engineers, Pressure Vessels and Piping Division (Publication) PVP, 146, 29-35.
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  Abstract: In this paper, the dynamic response of delamination cracks in a layered fiber reinforced composite plate is analytically studied. The plate is subjected to an antiplane loading and its surface response is computed in absence as well as in presence of delamination cracks. It is investigated here to what extent the surface response is influenced by the presence of internal delamination cracks. This study is important for nondestructive evaluation of internal damage in composites due to delamination. The problem is formulated in terms of integral equations in frequency domain. These equations are then solved by expanding the unknown cracks opening displacement in a complete set of Chebychev's polynomials, whose coefficients are solved by satisfying the traction free condition at the crack surface. The time histories are obtained numerically by inverting the spectra via fast fourier transform (FFT) routine. The results show significant influence of delamination crack geometries on the surface response of the plate.
• Karim, M. R., & Kundu, T. (1988). Transient surface response of layered isotropic and anisotropic half-spaces with interface cracks: SH case. International Journal of Fracture, 37(4), 245-262.
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  Abstract: The transient response of the surface of a layered isotropic or anisotropic half-space, with two interface cracks, excited by a plane SH-wave is investigated. The incident field is taken as a bulk wave. The governing equations along with boundary, regularity and continuity conditions across the interface are reduced to a coupled set of singular integral equations. Solutions of these equations are obtained by expanding unknown crack opening displacement (COD) in terms of a complete set of Chebyshev polynomials. As sample problems, the surface response of isotropic as well as anisotropic layered half-spaces with and without crack interactions is computed © 1988 Kluwer Academic Publishers.
• Karim, M. R., & Kundu, T. (1988). Transient surface response of layered isotropic and anisotropic half-spaces with interface cracks: SH case. International journal of fracture, 37(4), 245--262.
• Kundu, T. (1988). A theoretical analysis of acoustic microscopy with converging acoustic beams. Applied Physics B Photophysics and Laser Chemistry, 46(4), 325-331.
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  Abstract: A theoretical analysis is carried out to synthesize acoustic material signatures (AMS) of solid plates immersed in water. The distinctive feature of this analysis is that it avoids three major simplifying assumptions of the presently available techniques, which are, paraxial approximation, assumption of perfect reflection and Gaussian summation of the incident field. Presently available techniques can avoid some but not all of these simplifying assumptions for computing the AMS. In this paper the analysis is carried out for lowfrequency acoustic waves generated by a cylindrical transducer without a lens rod. Reasons for these changes in the conventional acoustic microscope geometry is given. The AMS is synthesized for an aluminium plate in presence as well as in absence of water on its one side. As expected a significant difference is observed between the signatures generated under these two situations. © 1988 Springer-Verlag.
• Kundu, T. (1988). A theoretical analysis of acoustic microscopy with converging acoustic beams. Applied Physics B, 46(4), 325--331.
• Kundu, T. (1988). Acoustic microscopy at low frequency. American Society of Mechanical Engineers (Paper), WA/APM51 6.
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  Abstract: A new design of the acoustic microscopy experimental setup is analyzed. The proposed microscope can operate at low frequency (0.1 to 3 MHz) and can be used in fracture mechanics, structural, and geomechanics applications. There is no buffer rod and the transducer is proposed to have a shape of a cylindrical shell to produce a line focus beam to measure material anisotropy. A line receiver is introduced instead of standard transducer-cum-receiver arrangements. A line receiver can receive only one specularly reflected ray and a few critically reflected rays and thus produces a less complicated interference pattern or acoustic material signature (AMS) which is easier to analyze. The shape of the generated AMS depends on the exact location of the receiver strip. Theoretically synthesized AMS of an aluminum plate for different receiver locations are presented.
• Kundu, T. (1988). Acoustic microscopy at low frequency. Journal of Applied Mechanics, Transactions ASME, 55(3), 545-550.
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  Abstract: A new design of the acoustic microscopy experimental setup is proposed and analyzed in this paper. The proposed microscope can operate at low frequency (0.1 to 3 MHz) and can be efficiently used in fracture mechanics, structural, and geomechanics applications. In the new design there is no buffer rod and the transducer is proposed to have a shape of a cylindrical shell to produce a line focus beam which is necessary to measure material anisotropy. A line receiver is introduced instead of standard transducer-cum-receiver arrangements. A line receiver can receive only one specularly reflected ray and a few critical reflected rays and thus produces less complicated interference pattern or acoustic material signature (AMS) which is easier to analyze.
• Kundu, T. (1988). Acoustic microscopy at low frequency. Journal of Applied Mechanics, 55(3), 545--550.
• Kundu, T. (1988). Dynamic interaction between two interface cracks in a three-layered plate. International Journal of Solids and Structures, 24(1), 27-39.
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  Abstract: In this paper, the dynamic interaction between two interface cracks, in a three-layered plate subjected to antiplane stress fields, is analytically studied. The problem is formulated in terms of a coupled set of integral equations, which are then solved by expanding the unknown crack opening displacements in a complete set of Chebyshev polynomials. The method is coded in a FORTRAN program and numerical results for a sample problem are presented. The results show that for the problem studied here one crack always reduces the crack opening displacement of its neighboring crack. © 1988.
• Kundu, T. (1988). On the nonspecular reflection of bounded acoustic beams. The Journal of the Acoustical Society of America, 83(1), 18--24.
• Pratap, R., & Kundu, T. (1988). A least squares finite element formulation for elastodynamic problems. International journal for numerical methods in engineering, 26(8), 1883--1891.
• Pratap, R., & Kundu, T. (1988). LEAST SQUARES FINITE ELEMENT FORMULATION FOR ELASTODYNAMIC PROBLEMS.. International Journal for Numerical Methods in Engineering, 26(8), 1883-1891.
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  Abstract: A residual finite element formulation is developed in this paper to solve elastodynamic problems in which body wave potentials are primary unknowns. The formulation is based on minimizing the square of the residuals of governing equations as well as all boundary conditions. Since the boundary conditions in terms of wave potentials are neither Dirichlet nor Neumann type it is difficult to construct a functional to satisfy all governing equations and boundary conditions following the variational principle designed for conventional finite element formulation. That is why the least squares technique is sought. All boundary conditions are included in the functional expression so that the satisfaction of any boundary condition does not become a requirement of the trial functions, but they should satisfy some continuity conditions across the interelement boundary to guarantee proper convergence. In this paper it is demonstrated that the technique works well for elastodynamic problems; however, it is equally applicable to any other field problem.
• Desai, C. S., Krempl, E., Kiousis, P. D., & Kundu, T. (1987). Constitutive Laws for Engineering Materials: Theory and Applications. Vol. I. Tucson, 1987.
• Kundu, T. (1987). Closure to``Discussion ofTransient Response of an Interface-Crack in a Layered Plate'''(1987, ASME J. Appl. Mech., 54, p. 245). Journal of Applied Mechanics, 54, 245.
• Kundu, T. (1987). The transient response of two cracks at the interface of a layered half space. International Journal of Engineering Science, 25(11-12), 1427-1439.
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  Abstract: In this paper, the transient response of two interface cracks, in a layered half space subjected to antiplane stress fields, is analytically studied. The problem is formulated in terms of a coupled set of integral equations, which are then solved by expanding the unknown crack opening displacements in a complete set of Chebyshev's polynomials. The method is coded in FORTRAN program and numerical results for a sample problem are presented. The results show that the response of one crack is significantly influenced by the presence of a bigger neighboring crack. © 1987.
• Kundu, T., & Hassan, T. (1987). A numerical study of the transient behavior of an interfacial crack in a bimaterial plate. International Journal of Fracture, 35(1), 55-69.
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  Abstract: In this paper we developed a numerical method to determine the transient stress intensity factor and crack opening displacement of an interfacial stationary crack in a bimaterial plate subjected to time dependent anti-plane shear stress on the surfaces of the plate. A bimaterial plate of finite length of dissimilar elastic, isotropic laminae with Griffith type of crack at the interface is analyzed. For the numerical method the finite element equations are derived in the frequency domain from a variational principle. The stress intensity factors in the frequency domain are evaluated from the displacements, which are obtained upon solving the finite element equations. The transient stress intensity factor is then obtained by numerical Fourier inversion technique using the Fast Fourier Transform (FFT) routine. Quarter point elements and transition elements are used to model the crack tip singularity. © 1987 Martinus Nijhoff Publishers.
• Kundu, T., & Hassan, T. (1987). A numerical study of the transient behavior of an interfacial crack in a bimaterial plate. International journal of fracture, 35(1), 55--69.
• Kundu, T. (1986). TRANSIENT RESPONSE OF AN INTERFACE-CRACK IN A LAYERED PLATE.. American Society of Mechanical Engineers (Paper).
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  Abstract: In this paper, the transient response of an interface crack, in a two layered plate subjected to an antiplane stress field, is analytically computed. The problem is formulated in terms of semi-infinite integrals following the technique developed by Neerhoff (1979). It has been shown that the major steps of Neerhoff's technique, which was originally developed for layered half-spaces, can also be applied to layered plate problems. An improved method for manipulation of semi-infinite singular integrals is also presented here. Finally, the new method is coded in FORTRAN program and numerical results for a sample problem are presented.
• Kundu, T. (1986). TRANSIENT RESPONSE OF AN INTERFACE-CRACK IN A LAYERED PLATE.. Journal of Applied Mechanics, Transactions ASME, 53(3), 579-586.
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  Abstract: In this paper, the transient response of an interface crack, in a two layered plate subjected to an antiplane stress field, is analytically computed. The problem is formulated in terms of semi-infinite integrals following the technique developed by Neerhoff (1979). It has been shown that the major steps of Neerhoff's technique, which was originally developed for layered half-spaces, can also be applied to layered plate problems. An improved method for manipulation of semi-infinite singular integrals is also presented here. Finally, the new method is coded in FORTRAN program and numerical results for a sample problem are presented.
• Kundu, T. (1986). Transient response of an interface-crack in a layered plate. Journal of Applied Mechanics, 53(3), 579--586.
• Kundu, T., & Mal, A. K. (1986). Acoustic material signature of a layered plate. International Journal of Engineering Science, 24(12), 1819-1829.
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  Abstract: A technique is presented for the theoretical calculation of the acoustic material signature (AMS) of a multilayered plate with its bottom surface free of traction. The layers are composed of homogeneous isotropic linearly elastic materials and are assumed to be firmly bonded at the interfaces. The plate model can serve to represent either a self supporting membrane, or a multilayered composite with extensive debonding on a plane parallel to the layers. Calculated AMS curves are presented for a uniform plate, a two layered plate and a two layered half-space at 60 MHz exciting frequency. The striking differences in these curves indicate the possibility of using them as quantitative diagnostics for extensive debonding in a layered specimen. © 1986.
• KUNDU, T., & MAL, A. K. (1985). ELASTIC-WAVES IN A MULTILAYERED SOLID DUE TO A DISLOCATION SOURCE. WAVE MOTION, 7(5), 459-471.
• Kundu, T., & Mal, A. K. (1985). Elastic waves in a multilayered solid due to a dislocation source. Wave Motion, 7(5), 459-471.
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  Abstract: A modified version of the wave number integral approach is applied to the calculation of the motion produced in a multilayered solid by dynamic sources. A new method of pole removal is introduced to facilitate separation of the continuous and the discrete spectral responses of the medium. The well-known numerical difficulties associated with the calculation of the integrands of the continuous spectra and the mode shapes of the discrete spectra are avoided through the use of delta matrices. Special numerical integration schemes are used to calculate the body wave integrals accurately at smaller distances and higher frequencies. © 1985.
• Kundu, T., & Mal, A. K. (1985). Elastic waves in a multilayered solid due to a dislocation source. Wave motion, 7(5), 459--471.
• Kundu, T., Mal, A. K., & Weglein, R. D. (1985). CALCULATION OF THE ACOUSTIC MATERIAL SIGNATURE OF A LAYERED SOLID.. Journal of the Acoustical Society of America, 77(2), 353-361.
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  Abstract: A theory is presented for the calculation of the acoustic material signature of a multilayered elastic half-space overlain by a fluid. The solid layers are composed of homogeneous isotropic linearly elastic materials and are firmly bonded at the interfaces. The calculation procedure is valid at an arbitrarily high frequency of excitation. Results are presented for a uniform, a single layered and a four layered model of the half-space at two frequencies of excitation; one moderate (35 MHz) and the other relatively high (370 MHz). Several new features of the material signatures and their possible use in the material characterization of layered specimen are indicated.
• Kundu, T., Mal, A. K., & Weglein, R. D. (1985). Calculation of the acoustic material signature of a layered solid. The Journal of the Acoustical Society of America, 77(2), 353--361.
• Kundu, T. (1984). COMPUTATION OF SURFACE MOTION IN A STRATIFIED HALF SPACE..
• Mal, A. K., & Kundu, T. (1984). CALCULATION OF THE ACOUSTIC MATERIAL SIGNATURE OF A LAYERED SOLID.. Review of Progress in Quantitative Nondestructive Evaluation, 3 B, 1027-1033.
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  Abstract: One of the newer techniques that has been used to study simple solid specimens, viz. the focused-beam, reflection mode acoustic microscopy (FRAM) is described. In an effort to provide a better understanding of the FRAM approach a comprehensive theoretical model of the system is developed in which all of the wave phenomena occurring within the solid are fully accounted for. In this paper the basic ingredients of the theory are briefly described and representative new results obtained are presented.
• Mal, A. K., Kundu, T., & Xu, P. -. (1984). ON THE SURFACE RESPONSE OF A MULTILAYERED SOLID TO A DISLOCATION SOURCE.. American Society of Mechanical Engineers, Pressure Vessels and Piping Division (Publication) PVP, 80, 29-48.
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  Abstract: A modified version of the wavenumber integral approach is applied to the calculation of the surface motion produced in a multilayered half space by a point dislocation. A new method of pole removal is introduced to facilitate separation of the continuous (body wave) and the discrete (surface wave) spectral responses of the medium.
• Kundu, T., & Mal, A. K. (1981). DIFFRACTION OF ELASTIC WAVES BY A SURFACE CRACK ON A PLATE.. Journal of Applied Mechanics, Transactions ASME, 48(3), 570-576.
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  Abstract: The interaction of time harmonic elastic waves with an edge crack in a plate is studied. The crack is assumed to be normal to the plate surface and its depth small compared to plate thickness. Only plane strain deformations are considered. The incident waves are assumed to be either plane body waves (compressional (P) or inplane shear (SV)) of arbitrary angle of propagation or surface Rayleigh waves propagating at right angles to the crack. For each incident wave type the complete high frequency diffracted field on the plate surface is calculated. Solution is obtained by the application of an asymptotic theory of diffraction. Application to ultrasonic inspection techniques is indicated.
• Kundu, T., & Mal, A. K. (1981). Diffraction of elastic waves by a surface crack on a plate. Journal of Applied Mechanics, 48(3), 570--576.

Proceedings Publications

• Alnuaimi, H., Amjad, U., & Kundu, T. (2023). Acoustic source localization in composite plates using non-linear ultrasonic technique-SPC-I. In Health Monitoring of Structural and Biological Systems XVII, 12488.
• Alnuaimi, H., Amjad, U., Russo, P., Lopresto, V., & Kundu, T. (2023). A Non-Linear Ultrasonic Approach Using a Fine-Tuned Experimentally Defined Frequency for Structural Health Monitoring of Composite Plates. In 49th Annual Review of Progress in Quantitative Nondestructive Evaluation, 86595.
• Amjad, U., Alnuaimi, H., Nikvar-Hassani, A., Bokhari, I., Zhang, L., & Kundu, T. (2023). Real-Time Structural Health Monitoring of Concrete Using the Non-Linear Ultrasonic SPC-I Technique. In 49th Annual Review of Progress in Quantitative Nondestructive Evaluation, 86595.
• Hu, B. o., Che, R., Wang, J., He, X., Li, L., & Kundu, T. (2023). Analytical investigation into the flexural behavior of steel tubular truss-and-concrete (STTC) composite beams. In Structures, 50.
• Li, Z., Liu, J., Fu, L., Cui, Z., & Kundu, T. (2023). Effect of axial stresses on longitudinal guided waves in pipe structures. In Health Monitoring of Structural and Biological Systems XVII, 12488.
• Castellano, A., Fraddosio, A., Kundu, T., & Piccioni, M. D. (2022). SPC non-linear ultrasonic technique for detecting adhesion defects in FRCM reinforcements for masonry constructions. In Health Monitoring of Structural and Biological Systems XVI, 12048.
• Park, S., Bokhari, I., Alnuaimi, H., Amjad, U., Fleischman, R., & Kundu, T. (2022). Inspection of steel tube welded joint using nonlinear ultrasonic technique. In Health Monitoring of Structural and Biological Systems XVI, 12048.
• Zhou, Z., Cui, Z., Yin, S., & Kundu, T. (2022). A rapid acoustic source localization technique in early warning of building material damage-a numerical study. In Health Monitoring of Structural and Biological Systems XVI, 12048.
• Castellano, A., Fraddosio, A., Kundu, T., & Piccioni, M. D. (2021). Non-destructive assessment of the adhesion at the interface between FRCM reinforcements and masonry substrates by non-linear ultrasonic technique. In 12th International Conference on Structural Analysis of Historical Constructions-SAHC.
• Park, S., Alnuaimi, H., Amjad, U., & Kundu, T. (2021). Evaluating the Degree of Nonlinearity by Applying the Nonlinear SPC-I Technique in the FEM Simulation of Materials With Breathing Cracks. In Quantitative Nondestructive Evaluation, 85529.
• Park, S., Alnuaimi, H., Hayes, A., Sitkiewicz, M., Amjad, U., Muralidharan, K., & Kundu, T. (2021). Linear and nonlinear analysis of additively manufactured material with different porosity induced by varying material printing speed using guided acoustic waves. In Quantitative nondestructive evaluation, 85529.
• Zhou, Z., Cui, Z., & Kundu, T. (2021). Acoustic source localization on a thin isotropic spherical shell. In Health Monitoring of Structural and Biological Systems XV, 11593.
• Fu, J., Cui, Z., Yin, S., & Kundu, T. (2020). Acoustic source localization on the surface of a cylindrical pressure vessel. In Health Monitoring of Structural and Biological Systems XIV, 11381.
• Kundu, T. (2019). Smart nondestructive evaluation and health monitoring of structural and biological systems II(San Diego CA, 3-5 March 2003). In SPIE proceedings series.
• Kundu, T. (2019, July 28-August 1, 2019). Experimental Verification of Acoustic Source Localization Technique in Heterogeneous Plates. In 14th International Conference of Theory and Computation of Acoustics.
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  Yin, S., J. Fu, T. Kundu and Z. Cui, “Experimental Verification of Acoustic Source Localization Technique in Heterogeneous Plates”, the 14th International Conference of Theory and Computation of Acoustics, Beijing, China, July 28-August 1, 2019.
• Kundu, T. (2019, September, 2019). Feasibility of a new nonlinear ultrasonic technique for monitoring damage in composite plates. In 12th International Workshop on Structural Health Monitoring.
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  Alnuaimi, H. U. Amjad, P. Russo, V. Lopresto and T. Kundu, “Feasibility of a new nonlinear ultrasonic technique for monitoring damage in composite plates” Proceedings of the 12th International Workshop on Structural Health Monitoring, Stanford University, September 10-12, 2019.
• Amjad, U., Yadav, S. K., Dao, C. M., Dao, K., & Kundu, T. (2016). Advanced signal processing technique for damage detection in steel tubes. In Health Monitoring of Structural and Biological Systems 2016, 9805.
• Amjad, U., Yadav, S. K., Dao, C. M., Dao, K., & Kundu, T. (2016). Advanced signal processing technique for damage detection in steel tubes. In SPIE Smart Structures and Materials+ Nondestructive Evaluation and Health Monitoring.
• Hafezi, M. H., Alebrahim, R., & Kundu, T. (2016). Crack propagation modeling using Peridynamic theory. In Health Monitoring of Structural and Biological Systems 2016, 9805.
• Hafezi, M. H., Alebrahim, R., & Kundu, T. (2016). Crack propagation modeling using Peridynamic theory. In SPIE Smart Structures and Materials+ Nondestructive Evaluation and Health Monitoring.
• Park, W. H., Packo, P., & Kundu, T. (2016). Acoustic source localization in an anisotropic plate without knowing its material properties: a new approach. In Health Monitoring of Structural and Biological Systems 2016, 9805.
• Amjad, U., Yadav, S. K., Nguyen, C. H., Ehsani, M., & Kundu, T. (2015). Guided wave technique for non-destructive testing of StifPipe. In Health Monitoring of Structural and Biological Systems 2015, 9438.
• Amjad, U., Yadav, S. K., Nguyen, C. H., Ehsani, M., & Kundu, T. (2015). Guided wave technique for non-destructive testing of StifPipe. In SPIE Smart Structures and Materials+ Nondestructive Evaluation and Health Monitoring.
• Eiras, J. N., Kundu, T., Popovics, J. S., Monz'o, J., Borrachero, M. V., & Pay'a, J. (2015). Monitoring accelerated carbonation on standard Portland cement mortar by nonlinear resonance acoustic test. In Health Monitoring of Structural and Biological Systems 2015, 9438.
• Eiras, J. N., Kundu, T., Popovics, J. S., Monz'o, J., Borrachero, M. V., & Pay'a, J. (2015). Monitoring accelerated carbonation on standard Portland cement mortar by nonlinear resonance acoustic test. In SPIE Smart Structures and Materials+ Nondestructive Evaluation and Health Monitoring.
• Grabowski, K., Gawronski, M., Nakatani, H., Packo, P., Baran, I., Spychalski, W. L., Staszewski, W. J., Uhl, T., & Kundu, T. (2015). Distance-domain based localization techniques for acoustic emission sources: a comparative study. In Health Monitoring of Structural and Biological Systems 2015, 9438.
• Grabowski, K., Gawronski, M., Nakatani, H., Packo, P., Baran, I., Spychalski, W., Staszewski, W., Uhl, T., & Kundu, T. (2015). Distance-domain based localization techniques for acoustic emission sources: a comparative study. In SPIE Smart Structures and Materials+ Nondestructive Evaluation and Health Monitoring.
• Grabowski, K., Nakatani, H., Gawronski, M., Packo, P., Staszewski, W. J., Uhl, T., & Kundu, T. (2015). Optimization of acoustic source localization in large plates. In 10th International Workshop on Structural Health Monitoring: System Reliability for Verification and Implementation, IWSHM 2015.
• Hafezi, M. H., & Kundu, T. (2015). A new model for predicting fatigue damage. In 10th International Workshop on Structural Health Monitoring: System Reliability for Verification and Implementation, IWSHM 2015.
• Kundu, T. (2015). Health Monitoring of Structural and Biological Systems 2015. In Proc. of SPIE Vol, 9438.
• Radzie'nski, M., Mieloszyk, M., Rahani, E. K., Kundu, T., & Ostachowicz, W. (2015). Heat induced damage detection in composite materials by terahertz radiation. In Health Monitoring of Structural and Biological Systems 2015, 9438.
• Radzie'nski, M., Mieloszyk, M., Rahani, E. K., Kundu, T., & Ostachowicz, W. (2015). Heat induced damage detection in composite materials by terahertz radiation. In SPIE Smart Structures and Materials+ Nondestructive Evaluation and Health Monitoring.
• Eiras, J. N., Kundu, T., Popovics, J. S., Monz'o, J., Soriano, L., & Pay'a, J. (2014). Evaluation of frost damage in cement-based materials by a nonlinear elastic wave technique. In Health Monitoring of Structural and Biological Systems 2014, 9064.
• Eiras, J. N., Kundu, T., Popovics, J. S., Monz'o, J., Soriano, L., & Pay'a, J. (2014). Evaluation of frost damage in cement-based materials by a nonlinear elastic wave technique. In SPIE Smart Structures and Materials+ Nondestructive Evaluation and Health Monitoring.
• Habib, A., Pluta, M., Amjad, U., Shelke, A., Pietsch, U., Kundu, T., Wannemacher, R., & Grill, W. (2014). 2E4-1. In Proceedings of Symposium on Ultrasonic Electronics, 35.
• Mahmoudabadi, E., Amjad, U., Kundu, T., & Saadatmanesh, H. (2014). Effect of applied load on the nondestructive measurement of concrete strength. In Health Monitoring of Structural and Biological Systems 2014, 9064.
• Mahmoudabadi, E., Amjad, U., Kundu, T., & Saadatmanesh, H. (2014). Effect of applied load on the nondestructive measurement of concrete strength. In SPIE Smart Structures and Materials+ Nondestructive Evaluation and Health Monitoring.
• Mahmoudabadi, E., Amjad, U., Kundu, T., Saadatmanesh, H., & Kundu, T. (2014). Effect of applied load on the non-destructive measurement of concrete strength. In HEALTH MONITORING OF STRUCTURAL AND BIOLOGICAL SYSTEMS 2014, 9064.
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  Nondestructive measurement of the concrete strength is an important topic of research. Among different nondestructive testing (NDT) methods the ultrasonic pulse velocity (UPV) technique is the most popular method for concrete strength estimation. While measuring concrete strength by this method almost all researchers have neglected the effect of applied stress or load on the concrete member. In this investigation attempts were made to properly incorporate the effect of the applied load on the strength prediction of concrete specimens from UPV value. To achieve this goal, 4 groups of concrete specimens with different values of final strength were made. Materials used for making cylindrical specimens of 3 inch diameter and 6 inch height included regular Portland cement, water and two types of aggregate - fine and coarse. After applying the load on the specimen in multiple steps - up to 70% of its failure strength f(c)'-the time of flight (TOF) value was measured for every loading step. The recorded results showed that applied load on the member has significant effect on the measured UPV value on concrete specimens. Therefore, to find the strength of the concrete from the UPV value, the applied load on the sample should be considered as an important factor that cannot be neglected.
• Amjad, U., Chi Hanh Nguyen, ., Yadav, S. K., Mahmoudabadi, E., Kundu, T., & Kundu, T. (2013). Change in Time-of-Flight of Longitudinal (axisymmetric) wave modes due to Lamination in Steel pipes. In HEALTH MONITORING OF STRUCTURAL AND BIOLOGICAL SYSTEMS 2013, 8695.
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  Investigations with the aid of longitudinal guided waves in cylindrical structures have been regularly carried out for non-destructive evaluation (NDE) and structural health monitoring (SHM). While earlier works concentrated on the amplitude reduction of the propagating waves due to structural anomalies in this work the change in time-of-flight is investigated. Longitudinal (axisymmetric) modes are excited by a PZT (Lead Zirconate Titanate) transducer for detection of any fluctuation or change in the surface of a steel pipe. Propagating waves are analyzed after proper signal processing. To observe the small change in TOF due to lamination on the surface of a steel pipe, cross-correlation technique is used to attain a higher temporal resolution. The experimental technique is discussed and the obtained results are presented in this paper.
• Amjad, U., Nguyen, C. H., Yadav, S. K., Mahmoudabadi, E., & Kundu, T. (2013). Change in time-of-flight of longitudinal (axisymmetric) wave modes due to lamination in steel pipes. In Health Monitoring of Structural and Biological Systems 2013, 8695.
• Eiras, J. N., Amjad, U., Mahmoudabadi, E., Pay'a, J., Bonilla, M., & Kundu, T. (2013). Monitoring ageing of alkali resistant glass fiber reinforced cement (GRC) using guided ultrasonic waves. In Health Monitoring of Structural and Biological Systems 2013, 8695.
• Eiras, J. N., Kundu, T., Popovics, J. S., Monz'o, J., Borrachero, M. V., & Paya, B. (2013). Monitoring material nonlinearity and attenuation variations in mortar subjected to freezing-thawing cycles. In Proceedings of Meetings on Acoustics 166ASA, 20.
• Mahmoudabadi, E., Eiras, J. N., Amjad, U., Pay'a, J., Saadatmanesh, H., & Kundu, T. (2013). Nondestructive detection of nonlinear behavior of plain and polymer concrete under cycling loading. In 9th International Workshop on Structural Health Monitoring: A Roadmap to Intelligent Structures, IWSHM 2013.
• Mahmoudabadi, E., Eiras, J. N., Amjad, U., Paya, J., Saadatmanesh, H., Kundu, T., & Chang, F. (2013). Nondestructive Detection of Nonlinear Behavior of Plain and Polymer Concrete Under Cycling Loading. In STRUCTURAL HEALTH MONITORING 2013, VOLS 1 AND 2, 1928-1935.
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  Polymer concrete is a composite material that uses polymeric resin as aggregate filler. This type of concrete is strong, durable, non-absorbent and chemical resistant. Under cyclic loadings pre-existing cracks inside both conventional concrete and polymer concrete may grow and cause catastrophic failure of the structure. Structural failure under cyclic loading is also known as the fatigue failure. This study aims to investigate the behavior of plain and polymer concrete under the cyclic loading or fatigue. The specimens used for this study included cylindrical specimens of 3 inch diameter and 6 inch in length. They were subjected to compressive load for various numbers of cycles. The applied load was gradually increased. After the loading-unloading cycles, nonlinear impact resonance acoustic spectroscopy (NIRAS) test was carried out on the samples using instrumented impact hammer. The degree of nonlinearity in the concrete specimens was measured by recording the shift in the resonance frequency as the impact energy increased. The results indicated that for conventional concrete specimens the material nonlinearity increased with the number of loading cycles and the applied load magnitude. However, for polymer concrete it remained almost unchanged. Experimental results from conventional plain concrete and polymer concrete specimens were compared.
• Nakatani, H., Hajzargarbashi, T., Ito, K., Kundu, T., & Takeda, N. (2013). Locating point of impact on an anisotropic cylindrical surface using acoustic beamforming technique. In Key Engineering Materials, 558.
• Habib, A., Shelke, A., Pietsch, U., Kundu, T., & Grill, W. (2012). Determination of the transport properties of ultrasonic waves traveling in piezoelectric crystals by imaging with Coulomb coupling. In Health Monitoring of Structural and Biological Systems 2012, 8348.
• Habib, A., Shelke, A., Pietsch, U., Kundu, T., & Grill, W. (2012, January). Determination of the transport properties of ultrasonic waves traveling in piezo-electric crystals by imaging with Coulomb coupling. In Proceedings of SPIE - The International Society for Optical Engineering, 8348.
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  Abstract: Coulomb coupling has been applied for imaging of bulk and guided acoustic waves propagating in a 0.5 mm thick, z cut Lithium Niobate single-crystal. The excitation and detection of acoustic waves was performed by localized electrical field probes. The developed scheme has been applied to imaging of the transport properties of skimming longitudinal and guided acoustic waves. A short pulse of 20 ns has been used for the excitation of acoustic waves. Broadband coupling is achieved since neither mechanical nor electrical resonances are involved. The attenuation of acoustic waves in piezoelectric crystals is studied by this method. A thin film of conductive silver paint was deposited on the surface of the crystal acting as an acoustic attenuator inducing also mass loading effects and shortening of electrical fields. The group velocities of the propagating acoustic waves for both conditions, with and without the conductive silver paint film, are determined from the propagation of the acoustic wave fronts. © 2012 SPIE.
• Habib, A., Shelke, A., Pluta, M., Pietsch, U., Kundu, T., & Grill, W. (2012). Scattering and attenuation of surface acoustic waves and surface skimming longitudinal polarized bulk waves imaged by Coulomb coupling. In AIP Conference Proceedings, 1433.
• Korde, N., & Kundu, T. (2012). Guided waves for monitoring heat treatment duration and material hardness. In Health Monitoring of Structural and Biological Systems 2012, 8348.
• Korde, N., & Kundu, T. (2012, January). Guided waves for monitoring heat treatment duration and material hardness. In Proceedings of SPIE - The International Society for Optical Engineering, 8348.
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  Abstract: Elastic properties of materials can be easily determined from the ultrasonic wave velocity measurement. However, material hardness cannot be obtained from the ultrasonic wave speed. Heat treatment and aging affect the microstructure of materials changing their hardness and strength. In this study it is investigated how the attenuation of ultrasonic guided waves is affected by the duration of heat treatment and varying material hardness. To this aim six identical Aluminum 2024 alloy plate specimens were subjected to different durations of heat treatment at 150oC and were inspected nondestructively propagating Lamb waves through the specimens. Attenuation of the Lamb wave was found to be inversely related to the hardness. Rockwell Hardness test was performed to corroborate the ultrasonic observations. In comparison to Rockwell hardness test the ultrasonic inspection was found to be more sensitive to the heat treatment duration. From these results it is concluded that guided wave inspection method is a reliable and probably more desirable alternative for characterizing the hardness of heat treated materials. © 2012 SPIE.
• Korde, N., Kundu, T., & Kundu, T. (2012). Guided Waves for Monitoring Heat Treatment Duration and Material Hardness. In HEALTH MONITORING OF STRUCTURAL AND BIOLOGICAL SYSTEMS 2012, 8348.
  More info

  Elastic properties of materials can be easily determined from the ultrasonic wave velocity measurement. However, material hardness cannot be obtained from the ultrasonic wave speed. Heat treatment and aging affect the microstructure of materials changing their hardness and strength. In this study it is investigated how the attenuation of ultrasonic guided waves is affected by the duration of heat treatment and varying material hardness. To this aim six identical Aluminum 2024 alloy plate specimens were subjected to different durations of heat treatment at 150 degrees C and were inspected nondestructively propagating Lamb waves through the specimens. Attenuation of the Lamb wave was found to be inversely related to the hardness. Rockwell Hardness test was performed to corroborate the ultrasonic observations. In comparison to Rockwell hardness test the ultrasonic inspection was found to be more sensitive to the heat treatment duration. From these results it is concluded that guided wave inspection method is a reliable and probably more desirable alternative for characterizing the hardness of heat treated materials.
• Kundu, T. (2012). A new technique for acoustic source localization in an anisotropic plate without knowing its material properties. In 6th European Workshop on Structural Health Monitoring, Dresden, Germany.
• Kundu, T. (2012). Health Monitoring of Structural and Biological Systems 2012.
• Nakatani, H., Hajzargarbashi, T., Ito, K., Kundu, T., & Takeda, N. (2012). Impact localization on a cylindrical plate by near-field beamforming analysis. In Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems 2012, 8345.
• Shelke, A., Brand, S., Kundu, T., Bereiter-Hahn, J., & Blase, C. (2012). Mechanical property quantification of endothelial cells using scanning acoustic microscopy. In Health Monitoring of Structural and Biological Systems 2012, 8348.
• Blase, C., Shelke, A., Kundu, T., & Bereiter-Hahn, J. (2011). Elastic characterization of swine aorta by scanning acoustic microscopy at 30 MHz. In Health Monitoring of Structural and Biological Systems 2011, 7984.
• Habib, A., Shelke, A., Pouta, M., Kundu, T., Pietsch, U., & Grill, W. (2011). 3E2-2 Holographic imaging of acoustic waves in piezoelectric ceramics by local electric field probes (Measurement Techniques, Imaging, Nondestructive Evaluation). In Proceedings of Symposium on Ultrasonic Electronics, 32.
• Hajzargarbashi, T., Nakatani, H., Kundu, T., & Takeda, N. (2011). Detecting the point of impact on a cylindrical plate by the acoustic emission technique. In Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems 2011, 7981.
• Koabaz, M., Hajzargarbashi, T., Kundu, T., & Deschamps, M. (2011). Prediction of the point of impact in an anisotropic plate. In Journal of Physics: Conference Series, 269.
• Rahani, E. K., Hajzargarbashi, T., & Kundu, T. (2011). Distributed Point Source Method and its Applications in Solving Acoustic Wave Scattering Problems. In Proceedings of Meetings on Acoustics 162ASA, 14.
• Rivollet, A., Placko, D., & Kundu, T. (2011). Introducing a user-friendly MATLAB-based application interface software (AIS) for DPSM modeling: applied to ultrasonic problems. In Health Monitoring of Structural and Biological Systems 2011, 7984.
• Shelke, A., Habib, A., Amjad, U., Pluta, M., Kundu, T., Pietsch, U., & Grill, W. (2011). Metamorphosis of bulk waves to Lamb waves in anisotropic piezoelectric crystals. In Health Monitoring of Structural and Biological Systems 2011, 7984.
• Yadav, S. K., Banerjee, S., & Kundu, T. (2011). Advanced DPSM approach for modeling ultrasonic wave scattering in an arbitrary geometry. In Health Monitoring of Structural and Biological Systems 2011, 7984.
• Yadav, S. K., Banerjee, S., & Kundu, T. (2011). On suitability of feature extraction techniques for local damage detection. In Nondestructive Characterization for Composite Materials, Aerospace Engineering, Civil Infrastructure, and Homeland Security 2011, 7983.
• Amjad, U., Tarar, K. S., Shelke, A., Kundu, T., Pluta, M., & Grill, W. (2010). Generalized representations and universal aspects of Lamb wave dispersion relations. In Health Monitoring of Structural and Biological Systems 2010, 7650.
• Das, S., Banerjee, S., & Kundu, T. (2010). Transient ultrasonic wave field modeling in an elastic half-space using distributed point source method. In Health Monitoring of Structural and Biological Systems 2010, 7650.
• Hajzargarbashi, T., Kundu, T., & Bland, S. (2010). A new algorithm for detecting impact point in anisotropic plates by the acoustic emission technique. In Health Monitoring of Structural and Biological Systems 2010, 7650.
• Banerjee, S., & Kundu, T. (2009). Modeling of energy transmission by piezoelectric wafer active sensors through Gaussian contact. In Health Monitoring of Structural and Biological Systems 2009, 7295.
• Bhise, P., Mukherjee, A., & Kundu, T. (2009). Adapative DPSM Technique. In tbc.
• Ghosh, B., Chakraborty, P., Singh, B. P., & Kundu, T. (2009). Anti-Resonant Interferometric Nonlinear Spectroscopy (ARINS) study of metal nanocluster-glass composites. In Journal of Physics: Conference Series, 185.
• Kundu, T., Placko, D., Yanagita, T., & Sathish, S. (2009). Micro intereferometric acoustic lens: mesh-free modeling with experimental verification. In Health Monitoring of Structural and Biological Systems 2009, 7295.
• Miller, T. H., Yanagita, T., Kundu, T., Grill, J., & Grill, W. (2009). Nondestructive inspection of reinforced concrete structures. In Health Monitoring of Structural and Biological Systems 2009, 7295.
• Bhise, P., Mukherjee, A., & Kundu, T. (2008). Distributed Point Source Model for Wave Propagation. In Proceedings of the 8th World Congress on Computational Mechanics.
• Dao, C. M., Das, S., Banerjee, S., & Kundu, T. (2008). Bounded Acoustic Beam in a Fluid Wedge Over a Solid Half Space: a Combined Theoretical/experimental Investigation. In AIP Conference Proceedings, 975.
• Das, S., Banerjee, S., & Kundu, T. (2008). Modeling of elastic wave scattering by a hole in a half-space. In Health Monitoring of Structural and Biological Systems 2008, 6935.
• Kundu, T., Das, S., & Jata, K. V. (2008). Point of impact prediction in anisotropic fiber reinforced composite plates from the acoustic emission data. In AIP Conference Proceedings, 975.
• Vasiljevic, M., Kundu, T., Grill, W., & Twerdowski, E. (2008). Recent advances on pipe inspection using guided waves generated by electromagnetic acoustic transducers. In Health Monitoring of Structural and Biological Systems 2008, 6935.
• Yanagita, T., Placko, D., & Kundu, T. (2008). Effect of transducer boundary conditions on the generated ultrasonic field. In Health Monitoring of Structural and Biological Systems 2008, 6935.
• Ahmad, R., & Kundu, T. (2007). Application of Gabor transform on cylindrical guided waves to detect defects in underground pipes. In Health Monitoring of Structural and Biological Systems 2007, 6532.
• Banerjee, S., Kundu, T., & Placko, D. (2007). An improved DPSM technique for modelling ultrasonic fields in cracked solids. In Health Monitoring of Structural and Biological Systems 2007, 6532.
• Kamanyi, A. E., Ngwa, W., Kundu, T., & Grill, W. (2007). Soft matter acoustics: non-destructive health monitoring of polymer blend films. In Nondestructive Characterization for Composite Materials, Aerospace Engineering, Civil Infrastructure, and Homeland Security 2007, 6531.
• Kundu, T., Banerjee, S., Das, S., & Dao, C. M. (2007, Sept. 11-13). Effect of a Fluid Wedge on the Wave Propagation along a Fluid-Solid Interface: A Modeling Approach. In Proceedings of the 6th Int. Workshop on Structural Health Monitoring, 1, 919-926.
• Kundu, T., Das, S., & Jata, K. V. (2007). An improved technique for locating the point of impact from the acoustic emission data. In Health Monitoring of Structural and Biological Systems 2007, 6532.
• Ahmad, R., Banerjee, S., & Kundu, T. (2006). Cylindrical guided waves for damage detection in underground pipes using wavelet transforms. In Smart Structures and Materials 2006: Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems, 6174.
• Banerjee, S., & Kundu, T. (2006). Scattering of ultrasonic waves by internal anomalies in plates immersed in a fluid. In Health Monitoring and Smart Nondestructive Evaluation of Structural and Biological Systems V, 6177.
• Kundu, T. (2006). Health monitoring and smart nondestructive evaluation of structural and biological systems V(27 February-1 March 2006, San Diego, California, USA). In Proceedings of SPIE, the International Society for Optical Engineering.
• Kundu, T., Reibel, R., & Jata, K. V. (2006). Fundamental ultrasonic wave propagation studies in a model thermal protection system (porous tiles bonded to aluminum bulkhead). In Health Monitoring and Smart Nondestructive Evaluation of Structural and Biological Systems V, 6177.
• Banerjee, S., & Kundu, T. (2005). Elastic wave propagation in corrugated plates. In Health Monitoring and Smart Nondestructive Evaluation of Structural and Biological Systems IV, 5768.
• Kundu, T., Blase, C., & Bereiter-Hahn, J. (2005). Determination of cell properties from single and multi layered cell models. In Health Monitoring and Smart Nondestructive Evaluation of Structural and Biological Systems IV, 5768.
• Na, W., Kundu, T., Ryu, Y., & Kim, J. (2005). Concrete filled steel pipe inspection using electro magnetic acoustic transducer (EMAT). In Smart Structures and Materials 2005: Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems, 5765.
• Ngwa, W., Luo, W., Kundu, T., & Grill, W. (2005). Acoustic phase micrographs in mesoscale materials characterization. In Health Monitoring and Smart Nondestructive Evaluation of Structural and Biological Systems IV, 5768.
• Panergo, R., Liu, C., Estroff, B., & Wang, W. (2005). Polymeric waveguide design of a 2D scanner. In Health Monitoring and Smart Nondestructive Evaluation of Structural and Biological Systems IV, 5768.
• Ahmad, R., & Kundu, T. (2004). Guided wave technique to detect defects in pipes using wavelet transform. In Proceedings of the Second European Workshop on Structural Health Monitoring.
• Banerjee, S., & Kundu, T. (2004). Elastic wave propagation in symmetrically periodic sinusoidal waveguide. In Health Monitoring and Smart Nondestructive Evaluation of Structural and Biological Systems III, 5394.
• Ngwa, W., Grill, W., & Kundu, T. (2004). Bio-soft-matter imaging and micrometrology by phase-sensitive ultrasonic microscopy. In Health Monitoring and Smart Nondestructive Evaluation of Structural and Biological Systems III, 5394.
• Kundu, T. (2003). Smart Nondestructive Evaluation and Health Monitoring of Structural and Biological Systems II. In Smart Nondestructive Evaluation and Health Monitoring of Structural and Biological Systems II, 5047.
• Placko, D., Kundu, T., & Ahmad, R. (2003). Ultrasonic field computation in the presence of a scatterer of finite dimension. In Smart Nondestructive Evaluation and Health Monitoring of Structural and Biological Systems II, 5047.
• Kundu, T. (2002). Smart Nondestructive Evaluation for Health Monitoring of Structural and Biological Systems, San Diego, CA, Mar. 18-19, 2002. In Proceedings of SPIE, the International Society for Optical EngineeringProceedings of SPIE, the International Society for Optical Engineering.
• Placko, D., Kundu, T., & Ahmad, R. (2002). Theoretical computation of acoustic pressure generated by ultrasonic sensors in the presence of an interface. In Smart Nondestructive Evaluation for Health Monitoring of Structural and Biological Systems, 4702.
• Xu, Y., McDonough, J. M., & Mengüç, M. P. (2002). Turbulence-radiation interactions in flames: A chaotic-map based formulation. In ASME 2002 International Mechanical Engineering Congress and Exposition.
• Jorgensen, C. S., Hasenkam, J. M., & Kundu, T. (2001). Measurement of material properties of hard and soft biological tissues by means of V (z) and V (f) curves obtained with acoustic microscopy. In Advanced Nondestructive Evaluation for Structural and Biological Health Monitoring, 4335.
• Jung, Y., & Kundu, T. (2001). Ultrasonic response to material fatigue. In Advanced Nondestructive Evaluation for Structural and Biological Health Monitoring, 4335.
• Keller, M. S., Kundu, T., & Desai, C. S. (2001). Use of lamb waves to predict current damaged state of mortar. In 2001 ASME International Mechanical Engineering Congress and Exposition.
• Kundu, T. (2001). Advanced Nondestructive Evaluation for Structural and Biological Health Monitoring. In Advanced Nondestructive Evaluation for Structural and Biological Health Monitoring, 4335.
• Kundu, T. (2001). Recent Advances of the Use Of Lamb Waves for Material Characterization. In IUTAM Symposium on Mechanical Waves for Composite Structures Characterization.
• Kundu, T., & Jorgensen, C. S. (2001). Importance of multiply reflected signals in V (z) curve analysis for material characterization by acoustic microscopes. In Proceedings of the 7th ASME NDE Tropical Conference-2001.
• Placko, D., & Kundu, T. (2001). Theoretical study of magnetic and ultrasonic sensors: dependence of magnetic potential and acoustic pressure on the sensor geometry. In Advanced Nondestructive Evaluation for Structural and Biological Health Monitoring, 4335.
• Towfighi, S., Kundu, T., & Ehsani, M. (2001). Elastic wave propagation in circumferential direction in anisotropic pipes. In 2001 ASME International Mechanical Engineering Congress and Exposition.
• Guo, D., & Kundu, T. (2000). Detection of Mechanical Damages in Pipes by Lamb Waves Generated by a New Sensor. In Proceedings of the, 5.
• Guo, D., & Kundu, T. (2000). Lamb wave sensors for detecting wall defects in pipes. In Nondestructive Evaluation of Highways, Utilities, and Pipelines IV, 3995.
• Jung, Y. C., Kundu, T., & Ehsani, M. (2000). Detection of internal defects in concrete panels by Lamb waves. In AIP Conference Proceedings, 509.
• Jung, Y., Na, W., Kundu, T., & Ehsani, M. R. (2000). Damage detection in concrete using Lamb waves. In Nondestructive Evaluation of Highways, Utilities, and Pipelines IV, 3995.
• Kundu, T., Potel, C., & Belleval, J. (2000). Near Lamb mode imaging of multilayered composite plates. In Nondestructive Evaluation of Aging Aircraft, Airports, and Aerospace Hardware IV, 3994.
• Kundu, T., Ehsani, M. R., Maslov, K. I., & Guo, D. (1998). Detection of Delamination Defects at the Concrete/FRP Composite Interface of Longitudinal and Lamb Waves. In Second International Conference on Composites in InfrastructureNational Science Foundation, 2.
• Kundu, T. (1996). Acoustic microscopy and lamb wave imagine.. In MICROSCOPY RESEARCH AND TECHNIQUE, 33.
• Yang, W., Kundu, T., & Ghosh, T. (1996). LAMB WAVE SCANNING FOR DETECTING MATERIAL DEFECTS IN MULTILAYERED CONPOSITE PLATES. In First International Conference on Composites in InfrastructureNational Science FoundationNational Sicence Foundation.
• Yang, W., & Kundu, T. (1994). Efficient use of lamb waves to characterize multilayered anisotropic plates. In Proceedings of the 1994 International Mechanical Engineering Congress and Exposition.
• Chia, J. H., Desai, C. S., Kundu, T., Basaran, C., & Prince, J. L. (1993). Unified constitutive modelling of interfaces and materials in semiconductor devices. In Proceedings of the 1993 ASME Winter Annual Meeting.
• Romanel, C., & Kundu, T. (1993). Analysis of deeply embedded structures in a layered half-space. In Proceedings of the 12th International Conference on Offshore Mechanical and Arctic Engineering (OMAE 1993).
• Bereiter-Hahn, J., Berghofer, F., Kundu, T., Penzkofer, C., & Hillmann, K. (1992). Evaluation of mechanical properties of cells by scanning acoustic microscopy using V (z) characteristics. In Winter Annual Meeting of the American Society of Mechanical Engineers.
• Gracewski, S. M., & Kundu, T. (1992). Acousto-optics and Acoustic Microscopy: Presented at the Winter Annual Meeting of the American Society of Mechanical Engineers, Anaheim, California, November 8-13, 1992.
• Kundu, T., & Maxfield, B. (1992). New technique to detect surface waves and measure their velocities. In Winter Annual Meeting of the American Society of Mechanical Engineers.
• Awal, M. A., & Kundu, T. (1991). Acoustic material signature of an orthotropic plate. In Proe. Int. Conf. Constitutive Laws for Engr. Mat., Tucson, Az.
• Awal, M. A., & Kundu, T. (1991). Material characterization of composites by acoustic microscopy. In Winter Annual Meeting of the American Society of Mechanical Engineers.
• Kundu, T., & Karim, M. R. (1989). Interface cracks in an orthotropic layered half-space under impact loading. In Twelfth Canadian Congress of Applied Mechanics.
• Desai, C. S., Kundu, T., & Wang, G. (1988). Effect of specimen size on progressive damage and softening in simulated rock. In Offshore and Arctic Operations Synposium 1989.
• Kundu, T. (1988). ACOUSTIC MATERIAL SIGNATURE OF FIBER REINFORCED COMPOSITES. In Composite Material Technology, 1989: Presented at the Twelfth Annual Energy-Sources Technology Conference and Exhibition, Houston, Texas, January 22-25, 1989, 24.

Others

• Desai, C. S., Fishman, K. L., Ma, Y., Rigdy, D., & Kundu, T. (2019). Constitutive Modelling of Joints under Cyclic Loading. Part 1. Modelling and Testing of Idealized Rock Joints.
• Kundu, T. (2019). Modeling of Ultrasonic and Terahertz Radiations in Defective Tiles for Condition Monitoring of Thermal Protection Systems.
• Kundu, T., Banerjee, S., & Jata, K. V. (2019). An Experimental Investigation of Guided Wave Propagation in Corrugated Plates Showing Stop Bands and Pass Bands (PREPRINT).
• Yang, W., Kundu, T., & Guba, S. (2019). An improved design for joints between CC composites and glidcop copper using three dimensional stress analysis.
• Placko, D. (2013). Advanced ultrasonic methods for material and structure inspection.
• Placko, D., Kundu, T., Cruau, A., & Liebeaux, N. (2012). Universal method for modeling the interactions between at least one wave and at least one object, the surface of each object defining an interface between at least two media.
• Kundu, T. (2008). Fundamentals of fracture mechanics.
• Placko, D. M., Liebeaux, N., & Kundu, T. (2008). Method of evaluating a physical quantity representative of an interaction between a wave and an obstacle.
• Kundu, T. (2007). Health monitoring of structural and biological systems 2007: 19-22 March 2007, San Diego, California, USA.
• Placko, D., & Kundu, T. (2007). DPSM for modeling engineering problems.
• Kundu, T. (2003). Ultrasonic nondestructive evaluation: engineering and biological material characterization.
• Desai, C. S. (2001). Computer Methods and Advances in Geomechanics: Proceedings of the Tenth International Conference on Computer Methods and Advances in Geomechanics: Tucson/Arizona/USA/7-12 January 2001.
• Mal, A. K. (1999). On the Recent Advances of the Ultrasonic Nondestructive Evaluation and Composite Material Characterization: Presented at the 1999 ASME International Mechanical Engineering Congress and Exposition, November 14-19, 1999, Nashville, Tennessee.
• Kundu, T. (1980). Diffraction pattern of elastic waves by a surface crack.