Particle-loaded composites for acoustic anechoic coatings

We consider here composite coating layers to be used as “acoustic absorbers” which are able to attenuate broad-banded acoustic signals and minimize reflection. In order to effectively attenuate the acoustic wave, a loaded composite coating layer is designed with a binder material and loading configuration combination that allows both impedance matching between the fluid and material front face as well as extinction of the signal due to scattering and absorption effects. We discuss in detail the scattering of elastic waves from elastic spheres and employ an exact Mie-scattering solution to this problem. We then develop a new formal hierarchy for the multiple scattering of elastic waves, which is used to calculate the bulk wave properties of the composite coating. Using these results we show the reflection coefficient for a composite coating layer as a function of scatterer size and coating thickness for a variety of cases.