A low-frequency short-channel sound absorber with elastic inner wall containing air cavities

Abstract Underwater sound absorption is an important way to ensure their safety performance, and how to achieve low-frequency sound absorption at sub-wavelength thickness is a major challenge. In this paper, a channel-type underwater acoustic metamaterial is designed, which is mainly composed of a water channel and an elastic inner wall with semi-cylindrical air cavities, aiming to change the propagation path of sound using elastic thin-walled vibrations in the structure and to dissipate sound energy. The finite element method is used to calculate the underwater sound absorption performance of the absorber, and the results show that compared with the water channel surrounded by the elastic inner wall, the inclusion of air cavities shifts the sound absorption to lower frequencies, and the thickness of the absorber (H = 40 mm) is 1/120 of the wavelength ( λ ), which achieves a better sub-wavelength effect. The mechanism of action of the absorber was analyzed and parameterized. Based on the above research results, a combined structure with multiple parameter gradients is designed, which achieves effective sound absorption of more than 0.5 in the frequency range of 290–960 Hz and 1200–2000 Hz, and this performance is verified by experiments. It provides a technical approach to improving the safety performance of underwater vehicles.