An underwater metamaterial for broadband acoustic absorption at low frequency

In order to study and further develop underwater acoustic absorption structures, we present an underwater metamaterial for broadband acoustic absorption in this study, which is composed of viscoelastic rubber, conical cavity, cylindrical oscillator and backing steel. Basis for design is the contribution of local resonance resonators to low frequency absorption of airborne sound. The accuracy of finite element calculation (FEA) is verified by the theoretical model established by transfer matrix (TM) method at radial coordinates. Relative to pure viscoelastic rubber and traditional cavity acoustic absorption structure, the proposed structure could show excellent broadband acoustic absorption performance below 10 kHz. The geometrical size, shape, and position of filler also affect the direction of shear wave propagation after the transformation, which is critical reason behind the broadband underwater acoustic absorption. Different geometries and material parameters also could adjust the acoustic absorption to a great extent. Underwater impedance tube experiment proves the correctness of the FEA and TM calculation results. These conclusions could potentially be used to the underwater acoustic absorption structure.