Acoustic metamaterials designed via acoustic impedance optimization for low-frequency quasi-perfect absorption at both low- and high-amplitude excitations

Abstract Cavity-resonant acoustic metamaterials are prone to absorption performance instability at high incident sound pressure levels (ISPLs) owing to nonlinear effects. We first propose an opposed dual-channel coiling-up space (ODC-CUS). The experimental results reveal that the sound absorption performance at the peak frequency varies with the ISPL. To address the absorption instability under high ISPL, an impedance optimization strategy is proposed. With the target acoustic impedance as the optimization objective, the metamaterial structure is inversely designed to achieve quasi-perfect sound absorption at both low and high-amplitude excitations. Using the slit width and the CUS width as optimization variables and the target acoustic impedance as the goal, the structural parameters of the ODC-CUS for single-frequency and multi-frequency targets are inversely determined. Experimental results show that the optimized single-frequency ODC-CUS unit achieves a peak absorption coefficient above 0.95 at low ISPL and maintains quasi-perfect absorption even as the ISPL rises to approximately 130 dB, while the optimized multi-frequency unit retains good absorption stability under varying ISPL. The proposed impedance optimization algorithm bypasses the need for complex nonlinear acoustic impedance modeling, offering a new avenue for the efficient inverse design of nonlinear-robust sound-absorbing metamaterials.