Low acoustic impedance arc-shaped chiral metamaterials for low-frequency and broadband underwater sound insulation

• A novel arc-shaped chiral metamaterial is designed to create strong impedance mismatch with water through its geometry. • It provides broadband low-frequency sound insulation at subwavelength thickness and maintains pressure resistance via enhanced stiffness. • The multifunctional performance is thoroughly validated by simulations and experiments. This work proposes an arc-shaped chiral metamaterial (ACM) for low-frequency underwater sound insulation. The equivalent parameters of the designed arc-shaped chiral lattice (ACL) in the metamaterial are derived and evaluated using homogenization method. It is demonstrated that the arc central angle serves as a key geometric parameter for tuning the ACM’s acoustic and mechanical properties. By strategically adjusting this angle, a continuous reduction in equivalent acoustic impedance can be achieved, thereby significantly enhancing impedance mismatch with water. Numerical results for the transmission loss (TL) demonstrate that the metamaterial, designed according to this principle, exhibits excellent low-frequency broadband performance for underwater sound insulation while maintaining a deep subwavelength thickness. Furthermore, a stiffness recovery mechanism is identified at a specific central angle, enabling the design of pressure-resistant configurations that maintain acoustic functionality under a certain hydrostatic pressure. Experimental measurements agree well with simulations, validating the proposed design methodology for developing high-performance underwater sound insulation metamaterials. The insights from this work offer a practical pathway and may aid in the future development of efficient, lightweight underwater sound-insulating metamaterials.