Nonspecular reflection of two- and three-dimensional acoustic beams from fluid-immersed plane-layered elastic structures

Abstract

This paper treats the interaction of two- and three-dimensional acoustic quasi-Gaussian beams with plane-layered elastic configurations. Emphasis is placed on the regime of nonspecular reflection, which is characterized by strong coupling between the specularly reflected beam and leaky waves supported by the structure. The present analysis generalizes previously published studies of these phenomena by allowing for arbitrarily collimated two- and three-dimensional beams as well as simultaneous excitation of multiple leaky waves. The substantially enriched range of nonspecular phenomena encountered under these generalized conditions is explained by examining the spectral content of the reflected and leaky wave constituents that participate in the interaction. By use of the complex source point (CSP) method for modeling quasi-Gaussian beams, the reflection problems are solved rigorously by wave-number spectral decomposition. Subsequent reduction by uniform asymptotic techniques yields physically meaningful wave-field contributions, which explain the phenomenology and also allow efficient computation. The accuracy of the CSP asymptotic algorithms is assessed by comparison with purely numerically generated reference data. The results establish the accuracy and versatility of the CSP strategy for a broad range of beam-interface conditions.