Underwater low-frequency sound absorption performance and broadband absorption design of membrane-type acoustic metamaterials

The underwater low-frequency sound absorption performance of membrane-type acoustic metamaterials (MAM) is investigated in this paper. The MAM unit is composed of a tensioned membrane, an upper cavity frame, a lower cavity frame, a steel backing and a cylindrical mass block located at the geometric center of the membrane. The sound absorption mechanism of MAM and the influence of critical structural parameters are analyzed by numerical simulation. The absorption performance of MAM is further optimized by the parallel combination design of multiple MAM units and the acoustical siphon effect. A design of MAM with 19 units is proposed to improve the absorption bandwidth. The calculation result demonstrates that the structure can effectively absorb sound in the low-frequency range of 250–750 Hz, and the average absorption coefficient is above 0.6. Lastly, the corresponding sample is fabricated, and the underwater sound absorption performance is tested in the standing wave tube. The accuracy of numerical simulation is validated by experiment.