Determination of effective medium parameters of an in-line cavity based acoustic metamaterials with visco-thermal losses

Abstract

The study concerns with defining effective medium parameters- such as refraction index, impedance, mass density and compressibility- of acoustic metamaterials via an inverse method with and without taking of visco-thermal effects into account. This is realized by transfer matrix method using effective medium theory through the homogenization of an acoustic metamaterial by means of a passive material. Visco-thermal effects are approximately defined in the transfer matrix equations by using Zwicker-Kosten model. The model is verified by finite element method in cases with and without visco-thermal effects. In the study, as an example, an in-line spherical cavity based acoustic metamaterial with and without visco-thermal losses is considered. The effect of visco-thermal losses on effective parameters and also on acoustic parameters such as transmission and absorption coefficients is clearly shown for the considered acoustic metamaterial.