Compressibility-near-zero acoustic metamaterial

This letter theoretically analyzes and experimentally demonstrates a novel class of compressibility-near-zero (CNZ) acoustic metamaterials, achieved by using resonant-type metamaterials, namely the Helmholtz resonator. We first present a closed analytical formula for the effective compressibility of the proposed unit cell and then show that two frequencies exist which may support CNZ propagation. We demonstrate how the choice of the actual operating CNZ frequency depends on the properties of the host and finally experimentally verify CNZ propagation of acoustic waves.