Continuous near-perfect sound absorption of a slit-resonator acoustic metastructure

Abstract

A novel slit-resonator acoustic metastructure (SRAM) composed of Helmholtz resonators and porous materials is proposed to achieve a continuous perfect sound absorption at 200–3000 Hz. The Helmholtz resonator utilizes the resonance effect for low-frequency acoustic energy attenuation, and when its neck is small enough, it can be considered as an air slit. The air slit acts as a channel, from which most acoustic waves enter the metastructure and are absorbed by porous materials. Porous materials absorb high-frequency sound waves through thermoviscous dissipation. Unlike traditional filling forms, porous materials are filled around the air slits. To analyze the acoustic performance of this metamaterial, theoretical models and finite element models are developed and experimentally verified. The SRAM with melamine foam and rock wool can reach an absorption effect better than 0.5 at 331–3000 Hz and reaches a peak of 0.946 at 501 Hz with a thickness of 50 mm. Using the genetic algorithm, the parameters of SRAM are optimized for efficient sound absorption over a wider bandwidth. The optimized SRAM obtains an absorption coefficient of 0.8 in the range of 400–3000 Hz with a thickness of 50 mm. This study provides a new method of low-frequency ultra-broadband sound absorption.