ASA 126th Meeting Denver 1993 October 4-8

1pUW2. Retroreflective backscattering of sound in water due to Lamb waves on plates with corners: Observations.

S. S. Dodd C. M. Loeffler P. L. Marston

Appl. Res. Lab., Univ. of Texas, Austin, TX 78713-8029

A leaky Lamb wave is known to be launched on a flat elastic surface plate in water when the surface normal lies near a cone whose symmetry axis gives the k vector of the incident sound. These water tank experiments with a 600-kHz sonar demonstrate that when the plate has a corner with edges meeting at angles of 90(degrees) and 45(degrees), the wave vector of the Lamb wave is reversed due to repeated reflections at the edges that form the corner. The resulting leaky radiation gives a pronounced enhancement of the backscattering that depends only weakly on the orientation of the corner. Reductions in amplitude with deviations of the corner angle from 90(degrees) and with tilts of the surface normal were observed and they generally support the approximate analysis of P. L. Marston et al. (Abstract 4pSA2 at this meeting). For a suitably cut randomly oriented plate, the retroreflective enhancement is more likely to be observed than the specular reflection since then the normal must lie on a narrow range of angles.