Perfect sound-absorbing metasurface using Helmholtz resonators with non-uniformly partitioned cavities by membranes

We propose a perfect sound-absorbing metasurface generating hybrid resonance in a way that membranes non-uniformly divide cavities of adjacent sub-wavelength Helmholtz resonators. The membranes are parallel to the bottom surface of the Helmholtz resonators, which is a horizontal partition. The resonance frequencies of Helmholtz resonators could be decreased by embedding the membranes, indicating that it is possible for perfect sound absorption to be achieved with a thinner metasurface. We perform finite element simulations to investigate the absorption characteristic of the Helmholtz resonators with embedded membranes, and we optimize geometrical parameters and locations of the embedded membranes for the metasurface to absorb over 90% sound energy at single frequency. We further investigate the effect of types of partitions such as horizontal and vertical ones on absorbing performance via finite element simulations.