SINGLE-MODE LAMB WAVE EXCITATION IN THIN PLATES BY HERTZIAN CONTACTS

We present novel techniques to selectively excite the lowest order sym metric (S-0) and antisymmetric (A(0)) Lamb wave modes in thin solid pl ates. Hertzian contacts are formed between the plates and the end of s pecially designed quartz rods which guide extensional waves generated by PZT-SH transducers bended at their other end. Mode selectivity is a chieved by applying shear and/or longitudinal traction at the edge or the surface of the plates according to the results of a two-dimensiona l normal mode theory. In aluminum plates, mode selectivity is measured as a function of frequency for different traction forces. With normal forces, A(0) mode selectivity of more than 46 dB is obtained for fd<0 .4 MHz mm. With antisymmetric shear traction at the edge of the plate, a selectivity exceeding 55 dB is achieved for single mode S-0 operati on. (C) 1996 American Institute of Physics.