Vibro-acoustics of porous materials - Waveguide modelling approach

The porous material is considered as a compound multi-layered waveguide (i.e. a fluid layer surrounded with elastic layers) with traction free boundary conditions. The attenuation of the vibro-acoustic waves in such a material is assessed. This approach is compared with a conventional Biot's model and a qualitative agreement in phase velocities as well as damping estimates is found. The waveguide model predicts four waves, out of which two are attenuated when the viscous fluid is considered (while the elastic layer being ideally lossless). One of these waves is found to be significantly controlled by the fluid viscosity, while for the other the effect of viscosity was observed for very small frequencies. The Biot's model predicts only one of these attenuated waves, where the latter one is not predicted. Thus the proposed waveguide approach provide additional information about the wave propagation in porous materials.