Negative and density-near-zero acoustic metamaterials based on quasi-two-dimensional phononic crystals

Abstract

A phononic crystal consisting of an array of cylindrical boreholes in a two dimensional waveguide has been fabricated and characterized. Reflectance and transmittance have been measured in a slab with seven layers of scatterers. The acoustic bands as well as the effective parameters have been extracted from experimental data, showing that the proposed structure behaves as an acoustic metamaterial with negative bulk modulus. In addition it is shown that the inclusion of anisotropic effects through angular-dependent structures inside the boreholes leads to metamaterials with double negative parameters. This feature allows the observation of interesting phenomena such as an acoustic tunneling, which has been predicted through full wave simulations in a density-near-zero metamaterial.