The influence of backward wave transmission on quantitative ultrasonic evaluation using Lamb wave propagation

In view of the various novel quantitative ultrasonic evaluation techniques developed using Lamb wave propagation, the influence of an important relate d phenomenon, backward transmission, is investigated in this paper. Using t he discrete layer theory and a multiple integral transform method, the surf ace displacement and velocity responses of isotropic plates and cross-ply l aminated composite plates due to the Lamb waves excited by parabolic- and p iston-type transmitting transducers are evaluated. Analytical expressions f or the surface displacement and velocity frequency response functions are d eveloped. Based on this a large volume of calculations is carried out. Thro ugh examining the characteristics of the surface displacement and velocity frequency response functions and, especially, the different propagation mod es' contributions to them, the influence of the backward wave transmission related to quantitative ultrasonic nondestructive evaluation applications i s discussed and some important conclusions are drawn. (C) 2000 Acoustical S ociety of America. [S0001-4966(99)04212-5].