Acoustic wave confinement by chiral waveguide made of Helmholtz resonators

Abstract

Confining sound and controlling acoustic wave propagation is of significant importance for efficient energy harvesting. We propose an acoustic waveguide that exists at the interface between two metamaterials consist of unit cells based on Helmholtz resonators arranged in opposite chirality, which gives good confinement of sound wave in the air for frequencies within the bulk band gap of the metamaterial. The amplitude of pressure attenuates by 3 dB within 1/3 of the lattice constant. This waveguide is shown to be robust to frequency and spatial disorders in the system, as long as the edge mode is situated in the bandgap. An acoustic circuit was formed by introducing disorders at sharp corners. Our simulations demonstrate that the acoustic impedance at the interface, as defined by the ratio of the local pressure to the sound velocity, is 3 orders of magnitude smaller than the bulk impedance of the metamaterial for the frequency of interest, giving rise to confinement of the sound wave.