UNDERWATER SOUND TRANSMISSION THROUGH PERIODICALLY VOIDED SOFT ELASTIC MEDIUMS

Periodically voided soft elastic mediums can be used for acoustic coating of underwater vehicles to reduce the chances of detection by sonar. In this work, analytical and numerical models are developed to study sound transmission through a soft elastic medium submerged in water. The soft elastic material contains periodically distributed voids with the aim to minimise transmission of sound waves through the medium. The numerical model is based on the finite element method. The analytical model is based on homogenization theory which allows modelling of the voided material as a homogeneous material using effective material parameters. Attenuation of sound pressure over a broad frequency range is attributed to the monopole type resonance of the voids. A single layer of voids as well as multiple layers of voids along the direction of propagation of sound are considered. Significant change in the resonance frequency of a single void is observed in the presence of voids in close proximity to each other due to resonance coupling. Results obtained from the analytical and numerical models are compared.