Underwater Low-Frequency Sound Absorbing Metamaterials Based on Wave-Mode Transformation and Local Resonance Mechanism

We present a low-frequency sound-absorbing metamaterial for underwater applications and verify that its sound-absorbing coefficient reaches above 0.7 within 45 to 300 Hz bandwidth and remains more than 0.9 within 110 to 300 Hz bandwidth by finite element method.The metamaterial unit structure consists of five groups of conical and cylindrical cavities, a rubber matrix, two metal vibrators and a steel backing.We first analyze that the high sound absorption performance of this structure at low-frequency is the result of two mechanisms of local resonance and wave-mode transformation.The finite element method results prove good sound absorption performance of the structure and explain the influence of changing the geometrical parameters of the structure on the sound absorption coefficient.The combined effect of the local resonance, wave-mode transformation and sound wave scattering mechanism made a great contribution to the structure's high sound absorption efficiency.The innovative design propose in this study has potential value in the research and application fields of underwater sound absorption.