ASA 126th Meeting Denver 1993 October 4-8

4pSA2. Retroflective backscattering of sound in water due to leaky waves on facets, plates, and corner truncations: Approximate theory.

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

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

A leaky Rayleigh (or Lamb) wave is known to be launched on a flat elastic surface (or plate) in water when the surface normal lies near a cone whose symmetry axis gives the k vector of the incident sound. If the surface has a corner with edges meeting at angles of 90(degrees), 45(degrees), 30(degrees),..., the wave vector of the leaky wave is exactly reversed due to repeated reflections at the edges that form the corner. The resulting leaky radiation is backscattered toward the source and depends only weakly on the orientation of the corner. The high-frequency cross section is large since the outgoing wave front is flat. For a suitably cut, randomly oriented facet or metal block, this effect is more likely to be observed than the specular reflection since then the normal must lie on a narrow range of angles. An approximate geometric theory for the amplitude is given. The mechanism also applies to circular cylindrical shells with 90(degrees) truncations.