Acoustic Characterization of Inhomogenous Layers using Finite Element Method

This study presents a finite element approach to estimate acoustic parameters of layers of arbitrary compositions using 2D and 3D models. In this approach the resonance frequency of a layer to be investigated is found by exciting the layer with plane waves and studying the reflected and transmitted sound pressure from the layer. Compressional and shear modes can be excited separately by varying the angle of incidence. A script for generating inhomogeneous layers with randomly distributed inclusions of arbitrary shape and size was developed for this study. A Matlab application was built for processing the result and comparison with analytical calculations. The 2D and 3D models were validated by comparing derived acoustic parameters of known materials with no more than 0.06% deviation from expected values. Estimated parameters for a layer of gold with 10.6% volume fraction of spherical inclusions of voids of 3 µm and 5 µm diameter was found to range from 2540 m/s to 2652 m/s for compressional sound speed and from 1039 m/s to 1067 for shear speed of sound.