Underwater Acoustic Absorbing Materials with Multiple Air Cavities: Modeling and Validation

An analytical method for calculating the acoustic performance of underwater acoustic absorbing materials with multiple air cavities is derived and verified using numerical method. The underwater acoustic absorbing material consist of a rubber-based absorber with five cylindrical air cavities embedded along the rotating axis. Several geometric configurations of the air cavities are analyzed with both the proposed analytical method and the numerical method. Predictions obtained using the transfer matrix method, developed based on effective medium theory, show strong agreement with the numerical simulations in the low-frequency range, thereby validating the proposed analytical approach. The presence of air cavities significantly improves the absorption coefficient by enhancing local rubber deformation and energy dissipation. Increasing the cavity volume shifts the absorption peak toward lower frequencies due to a reduction in effective wave speed and a resulting slow-wave effect. In addition, reducing the spacing between adjacent cavities further improves absorption, as the gradual impedance transition facilitates wave penetration and enhances overall energy loss. These results demonstrate that the configuration of the air-layer cavity plays a crucial role in optimizing the acoustic performance of underwater acoustic absorbing materials.