Ultrathin Underwater Sound-Absorbing Metasurface by Coupling Local Resonance with Cavity Resonance

An ultrathin underwater metasurface with low frequency, broadband, high-efficiency absorption, and high-hydrostatic-pressure-resistance performance is proposed based on the integrated principle of local resonance and cavity resonance. The design-parameter complexity is overcome by the global-optimization capability of the genetic algorithm. As a demonstration, an average sound-absorption coefficient of 92.3% at 500-10 000 Hz with an ultrathin thickness of 32 mm is achieved, including more than 99% soundabsorption coefficient at 4670-8630 Hz. In the proposed metasurface, the complex surface impedances of the three subsurfaces provide unique views for the high-efficiency sound-absorption coupling mechanism by the equivalent-circuit model. Further investigation demonstrates that the excellent property of highefficiency sound absorption is maintained under 4.5-MPa hydrostatic pressure. The proposed metasurface provides more possibilities for underwater noise suppression.