4aSA2. (Bragg mode)-(leaky mode) coupling due to a finite periodic array of scatterers on a submerged elastic layer.

Session: Thursday Morning, May 16

Time: 8:30

Author: Raymond J. Nagem
Author: Leopold B. Felsen
Author: Brian J. Collins
Location: Dept. of Aerospace and Mech. Eng., Boston Univ., 110 Cummington St., Boston, MA 02215


Coupling of energy into and out of submerged layered elastic topographies via scattering centers on the top surface is of interest for a variety of applications in bottom-interacting acoustics. To understand and parametrize the basic wave phenomena which are operative here, this study was begun with a simple model wherein a finite periodic array of scatterers situated on a single elastic layer is insonified by an incident plane wave. The problem is analyzed rigorously by spectral wave-number decomposition, and the scattered fields are obtained by asymptotic evaluation of the spectral intergrals. The results can be interpreted in terms of array-modified leaky waves and slab-modified Bragg modes, with Bragg-leaky mode coupling occurring due to end effects as well as bulk effects of the array. The coupling effects are optimized when one of the slab-modified modes is phased matched to one of the Bragg modes. The asymptotic algorithms are calibrated against numerically evaluated spectral integral reference solutions. Windowed space-wave-number processing is then applied to extract the above phenomenology from the reference data.

from ASA 131st Meeting, Indianapolis, May 1996