Effect of micro-slit entries on the sound absorption and size of a labyrinthine acoustic metamaterial

Abstract

Low frequency noise attenuation is a pressing issue in the field of acoustics and noise control. In this regard, labyrinthine acoustic metamaterials have shown high potential in achieving low frequency sound absorption. This paper presents two new acoustic metamaterial designs consisting of a labyrinthine of sub-wavelength straight folded air channels with a rectangular cross-section surrounded by sound hard boundaries, combined with a micro-perforated slit panel. Design 1 has two micro-slits at the end channels, whose lengths are the same as the width of labyrinthine channels. Design 2 has two micro-slits of unequal length at the end channels. A simulation study using COMSOL Multiphysics is conducted to check the effect of the slit lengths on the sound absorption of these metamaterials. It is found that having micro-slits with unequal lengths for sound wave entry leads to a higher absorption peak and a lower peak absorption frequency compared to that of micro-slits with equal lengths. Moreover, it leads to a better sound absorption performance with increasing thickness. The experimental results of the sound absorption coefficient are in good agreement with the simulation results. Thus, Design 2 can be used for extremely low frequency sound absorptions in machinery with space constraints.