Characterization and optimization of the angle dependent acoustic absorption of 2D infinite periodic surfaces of Helmholtz resonators.

Acoustic metamaterials have emerged as alternative solutions to achieve useful physical effects that differ from the ones obtained with traditional materials. In terms of sound absorption, previous works have addressed their potential as compact surfaces with high performance. Nevertheless, studies on their angle-dependent behavior are scarce. In this work, an analytic and a numerical model to estimate the performance of periodic surfaces with unit cells composed of 2D Helmholtz resonators are presented. By making use of these modeling tools, the absorption of surfaces with one and three different resonators is studied both as a function of incidence angle and frequency. Changes in the incidence angle can cause variation of the maximum absorption coefficient, the frequencies at which the maximum performance is observed, and the frequency range of significant absorption. Furthermore, the rate at which the performance changes as a function of the incidence angle is larger as the angle increases. Given the angle-dependency of these absorbers, a strategy to optimize the dimensions of the surfaces’ elements to maximize the absorption performance for predefined ranges of incidence angles and frequencies is presented.