Near-perfect and near-broadband sound absorption using acoustic metasurface

Abstract

A near-perfect and near-broadband sound absorption at low frequencies is achieved by using hybrid resonance in an acoustic metasurface. The metasurface for perfect absorption at N frequencies con-sists of two-dimensional periodic array of unit cells, which are composed of 2N meta-atoms. Each meta-atom is designed to acquire hybrid resonance at a target frequency by using two Helmholtz resonators of sub-wavelength scale whose cavities are coiled up. We design a metasurface exhibit-ing perfect sound-absorption at four different frequencies by using optimization based on a theoret-ical model. The proposed metasurface is fabricated by using 3D printing. The experimental results show near-perfect and near-broadband sound absorption in that the absorption coefficient is 0.91 on average over a broad frequency range between 360Hz to 540Hz. The normalized bandwidth of 80% absorption to the centre frequency is 0.44 since the experimental results show greater absorption coefficients than 0.8 over the frequency range from 360Hz to 540Hz.