Superior underwater sound-absorbing metasurface based on wave mode conversion and cavity-plate coupling resonance

Underwater sound-absorbing metasurfaces are critical for applications like underwater acoustic stealth and noise control. However, achieving both broadband and low-frequency absorption remains a significant challenge. In this work, we present a novel design of underwater sound-absorbing metasurface based on two mechanisms: wave mode conversion and cavity-plate coupling resonance. The optimized design achieves broadband (0.47-10 kHz) and low-frequency (down to sub-kilohertz, i.e., 0.47 kHz) absorption with a deep subwavelength thickness (50 mm, 1/63 wavelength at 0.47 kHz). We experimentally verify the design using various viscoelastic materials, and the results are highly consistent with simulations, demonstrating the excellent absorption performance of our design. Then, we conduct parametric sweeps to assess the contribution of each design parameter, providing further validation of the two underlying mechanisms. Our findings suggest that this novel design has great potential for engineering applications, facilitating the development of underwater sound-absorbing technologies.