OBSERVATION AND ANALYSIS OF ACOUSTIC-SIGNALS FOLLOWING THE 2ND OR 3RDFRONT SURFACE REFLECTIONS IN AN ACOUSTIC MICROSCOPE

In the normal mode of operation of an acoustic microscope, the propert ies of the sample are inferred from the time delay of the leaky Raylei gh wave signal with respect to the first specular reflection from the sample surface. In this paper, observations of similar leaky Rayleigh wave signals following the second and third front surface signals from the sample are reported. Included is a ray analysis of their origin, which identifies the second front surface as involving a Rayleigh wave in the lens and the third as involving a Rayleigh wave in the sample. It is suggested that the latter could be of significant practical int erest since, for a given lens, leaky Rayleigh waves can be excited on samples with lower velocities than those following the first specular reflection.