Acoustic metasurface for perfect absorption using helmholtz resonators with non-uniformly partitioned cavities by membranes

We propose an acoustic metasurface consisting of sub-wavelength Helmholtz resonators whose cavities are non-uniformly partitioned by membranes, aiming at perfect absorption of low-frequency sound with the aid of hybrid resonance. Compared to the existing unit cells based on Helmholtz resonators, the proposed ones with embedded membranes have lower resonance frequencies, which implies that it is possible to achieve perfect absorption of sound by using a thinner metasurface. This study provides a theoretical model for fast and accurate design considering the visco-thermal losses in narrow orifices and the higher-order modes of the membrane. By optimizing geometrical parameters and locations of the embedded membranes, we design the metasurface for perfect absorption based on the theoretical model. Experimental validation is performed in impedance tube via fabrication.