Acoustic waves in alternating fluid/solid layers

Abstract

This article describes the results of ultrasonic experiments made to investigate several features of wave propagation in parallel fluid/solid layer systems and compares the results to theory. Immersion experiments were made at frequencies from 0.2–2 MHz on systems composed of water/Plexiglas and water/aluminum parallel layers. The one wave normal to the layering, and the two waves that can propagate parallel to the layering were both observed. Key experimental results demonstrating anisotropy, wavenumber and frequency stop bands, and phase velocity dispersion are shown that are in agreement with theory. The exact analytical theory based on first principles and the corresponding model experiments have implications leading to a better understanding of Biot’s theory of long wavelength propagation in a fluid saturated porous elastic medium.