A skin made of micro floating raft arrays for low-frequency broadband underwater sound absorption

To improve the acoustic stealth performance of underwater vehicles, a novel skin is proposed by combining miniaturized floating raft arrays with viscoelastic surfaces. A mathematical model of the skin for studying the sound absorption characteristics is established by employing the effective medium theory, which is mutually verified with the finite element simulation model. The simulation results show that the normal impedance of the skin matches water, and the lateral deformation of the micro floating raft element promotes the conversion of longitudinal waves to transverse waves. Therefore, a perfect sound absorption state with an absorption coefficient of 1 is generated at a low frequency of 350 Hz. Through optimizing and recombing the micro floating raft elements, the average absorption coefficient attains 0.88 from 10 Hz to 30 kHz, where the high-efficiency frequency band with a sound absorption rate greater than 0.7 accounts for 91%. Additionally, the sound absorption performance of the skin in the sub-wavelength frequency range of 10 Hz∼2.1 kHz is significantly better than that of a uniform layer with equal thickness, while the mass of the skin is only about half that of the uniform layer. In general, the skin made of micro floating raft arrays provides a potential approach for achieving low-frequency broadband sound absorption and is great significance for the lightweight design of anechoic coatings.