Effective acoustic properties of a soft viscoelastic material layered with ideal or viscous fluids

This paper deals with the analysis of quasicompressional wave propagation in periodically layered fluid-solid systems, where the waves propagate parallel to the layers. Specifically, we consider a compliant solid material, such as a polymer, layered with fluids with significant density contrast, such as air, water, or mercury. The well-known Rytov system of equations is used to derive numerical wave mode solutions for arbitrary frequency. These numerical solutions are then compared with analytical asymptotic results derived by the authors (e.g., Krauklis waves and Scholte waves in soft materials) as well as results from the literature. Different mechanisms of frequency-dependent wave damping associated with the viscosity of the fluid, softness of the compliant material, and density contrast between the solid and fluid layers are identified. The results of these studies, such as the frequency-dependent phase velocity and attenuation, are interpreted by invoking the phenomenological framework of Biot theory of wave propagation in a fluid-saturated porous medium, for which the fast and the slow modes have been identified. Overall, convincing agreement between analytical and numerical results is obtained.