Underwater low-frequency sound absorption of water-saturated porous meta-material with metallic chamber

This study proposes a class of absorbers comprising a water-saturated porous meta-material and a metallic chamber for low-frequency underwater sound absorption. A conventional type, cylindrical water-saturated sintered fiber metal (SFM) composites with metallic chamber (CWSFMMC) is selected as a starting point and extensively studied through theoretical analyses, numerical simulations, and experimental measurements, showing outstanding absorption capabilities for underwater sound waves across a broad range of hydrostatic pressures to clarify the absorption mechanism of water-saturated porous material with a metallic chamber. Then, employing the criterion of an equivalent hydraulic radius, a geometric gradient corrugated-core-like channel is utilized to coil the single-layer water-saturated SFM, thus creating a water-saturated porous meta-material. This process establishes an innovative, optimized type of geometric gradient space-coiling porous underwater sound-absorbing metamaterial (GGSPM) through a combined theoretical approach with the impedance-transfer method, Biot's theory, and the SO algorithm. In addition, numerical simulation results indicated that the GGSPM achieves robust underwater sound absorption α≥0.9 within a sub-wavelength regime (∼λ/27 at 1480 Hz), mutually confirming the theoretical analysis. Furthermore, the performance under oblique incident waves (elevation angle γ_ea and azimuth angle γ_aa) and the influence of material-related parameters (porosity φ_s and fiber diameter d_f) and gradient-specific acoustic impedance characteristics-related parameters (numbers of channels n₂, n₃, and n₄) are explored, showing significant potential for the development of next-generation high-performance underwater sound-absorption materials.