Sound absorption using a two-scale checker-board meta-surface with micro Helmholtz resonators

Abstract

In this study, we propose an acoustic meta-surface consisting of Helmholtz resonators in sub-wavelength scales for the purpose of absorbing the acoustic wave with two distinct frequencies. The meta-surface has a checkerboard pattern of two unit modules: the first unit module has four Helmholtz resonators of two types (A1, B1), and the second unit module has four Helmholtz resonators of two types (A2, B2). We obtain approximately 80% of sound absorption for each frequency, and derive a user-friendly mathematical formula for the practical design of sound ab-sorber. In addition, we propose a modified geometry of meta-surface to minimize the total reflec-tivity when the incident wave has different amplitude for each frequency.