Hybrid Acoustic Metamaterial Based on Absorption Accumulation Peaks for a Broad Sound Energy Control

Abstract

Controlling sound energy over a wide spectrum of frequencies through structures with a subwavelength scale is a challenge in acoustics. In this sense, a hybrid acoustic metamaterial model (HAMM) that acts over a wide frequency spectrum is presented. The structure consists of a combination of a porous layer and an acoustic metamaterial (AMM). Two samples are evaluated to establish effective control of sound energy ($\alpha \ge 60\%$) between 450 and 6400 Hz with the structure reaching a maximum ratio of $\lambda /11.5$. Furthermore, the behavior of sound waves in the structure is explored through analysis of the sound pressure field, instantaneous particle velocity, and thermoviscous dissipation. One of the highlights of the HAMM is that it is composed of an AMM that has a low phase velocity. Thus, the ultra-slow sound in part of the structure allows the low-frequency resonance frequency to be shifted to lower frequencies. Another characteristic is that because of the accumulation of absorption peaks below the bandgap of the AMM, a low-frequency broadband absorption is guaranteed. Therefore, this work contributes substantially to advances in the area of sound energy control over a wide spectrum of frequencies through the use of different combined acoustic materials.