Underwater acoustic absorption using a periodically voided soft elastic medium

Abstract

A coating comprising periodic cavities in a soft rubber medium can significantly reduce the reflection of acoustic waves from a steel plate. In this work, analytical and numerical models are developed to study acoustic reflection and transmission through a single layer of periodic cylindrical voids embedded in a soft elastic medium with steel backing. The analytical model is based on effective medium approximation theory which allows modeling of a composite material as a homogeneous material using effective material properties. The numerical model is based on the finite element method and developed using commercial finite element code COMSOL Multiphysics. Minimal reflection and transmission and maximal absorption of sound waves in a broad frequency range is attributed to the monopole type resonance of voids. The monopole resonance frequency of voids in an array is shown to be significantly higher compared to the monopole resonance of a single void in an infinite medium due to resonance coupling. An analytical framework to predict the resonance frequency of voids in an array is presented. The effect of strong and weak coupling of void resonances on reflection and transmission characteristics is investigated. Non-dimensionalized results obtained from the analytical and numerical models are compared.