Nonspecular reflection of beams from liquid-solid interfaces

Abstract

Nonspecular reflection plays an important role in acoustic beam interaction with fluid-immersed elastic media. Such anomalous reflection is attributed to the strong interaction which occurs when the incident beam is phase-matched to one of the leaky waves supported by the structure. The properties of the incident beam as well as those of the interface geometry exert a marked influence on the observed nonspecular return. Previous investigations have been limited to rather special beam and interface conditions. The present study removes many of these limitations by allowing for arbitrarily collimated beams incident on plane and (cylindrically) curved layered geometries as well as simultaneous excitation of multiple leaky waves. By use of the complex source point (CSP) method for modeling quasi-Gaussian beams, the reflection problems are solved rigorously by wavenumber spectral decomposition. They are then reduced by asymptotic techniques to yield physically meaningful wavefield contributions, which explain the phenomenology and also allow efficient computation. The accuracy of the CSP asymptotic algorithms, and that of more restrictive conventional 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. While the present study is for two-dimensional problems, the method has also been extended to the three dimensional case. The data base generated by this method is the first step toward developing a strategy for extracting from data information about the interface conditions.