Enhancing the acoustic absorption of vegetation with embedded periodic metamaterials

The sound absorption of vegetation with embedded periodic metamaterials is investigated numerically and experimentally. Acoustical property of the vegetation can be described as that in a porous material. The physical parameters of vegetation in the numerical study are obtained by fitting the measured reflection and transmission coefficients with the simulated results. The embedded metamaterial is composed of two-layer oppositely oriented split tubes, which can achieve two resonant absorption peaks at wavelengths much larger than its thickness. Both absorption peaks can be easily controlled by adjusting the width of the metamaterial while keeping its thickness unchanged. It is demonstrated that the absorption performance can be significantly enhanced by embedding periodic metamaterials into the vegetation. The results can be explained by coupling the viscous and thermal losses of vegetations with the resonance phenomenon arising from the metamaterials. Moreover, sound absorption increases with increased incidence angles and vegetation thickness. When more than one metamaterial per spatial period is considered, additional absorption peaks are observed which can further broaden the effective absorption bandwidth. (C) 2020 Elsevier Ltd. All rights reserved.

Automated summary

This study investigated the sound absorption properties of vegetation embedded with periodic metamaterials both numerically and experimentally. It was found that embedding periodic metamaterials into vegetation can significantly enhance sound absorption performance. The metamaterial, composed of two-layer oppositely oriented split tubes, can achieve two resonant absorption peaks which can be easily controlled by adjusting the width while keeping the thickness unchanged. Additionally, when considering more than one metamaterial per spatial period, additional absorption peaks are observed, broadening the effective absorption bandwidth.