A method is described by which transient ultrasonic Lamb waves may be generated and detected within thin materials, using laser techniques. The material is thin enough that only the two lowest-order modes of Lamb waves need be considered. These are the a0 mode, which is dispersive in the thin plate limit, and the s0 mode, which is not. Signal processing techniques were used to determine the dispersion characteristics of the a0 mode, and the velocity of the s0 mode, in both aluminum and metallic glass samples. From these measurements, it was possible to estimate both the thickness of the samples and their elastic constants. The errors involved in such a measurement are discussed.
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Hutchins et al. (1989) studied this question.