Efficient broadband sound absorption exploiting rainbow labyrinthine metamaterials

TL;DR

This paper presents a novel, lightweight, and tunable broadband sound absorption panel using rainbow labyrinthine metamaterials, experimentally validated for effective noise mitigation in the 800-1400 Hz range.

Contribution

It introduces a design method for broadband sound absorbers using quasi-periodic labyrinthine cells with tunable resonance frequencies, validated through experiments.

Findings

Achieved near-ideal absorption in 800-1400 Hz range

Demonstrated tunability of resonance frequency with cell size and thickness

Validated effectiveness of rainbow labyrinthine metamaterials for noise reduction

Abstract

In this work, we demonstrate in a proof of concept experiment the efficient noise absorption of a 3-D printed panel designed with appropriately arranged space-coiling labyrinthine acoustic elementary cells of various sizes. The labyrinthine unit cells are analytically and numerically analysed to determine their absorption characteristics and then fabricated and experimentally tested in an impedance tube to verify the dependence of absorption characteristics on cell thickness and lateral size. The resonance frequency of the unit cell is seen to scale approximately linearly with respect to both thickness and lateral size in the considered range, enabling easy tunability of the working frequency. Using these data, a flat panel is designed and fabricated by arranging cells of different dimensions in a quasi-periodic lattice, exploiting the acoustic "rainbow" effect, i.e. superimposing the frequency response of the different cells to generate a wider absorption spectrum, covering the target frequency range, chosen between 800 and 1400 Hz. The panel is thinner and more lightweight compared to traditional sound absorbing solutions and designed in modular form, so as to be applicable to different geometries. The performance of the panel is experimentally validated in a small-scale reverberation room, and an absorption close to ideal values is demonstrated at the desired frequencies of operation. Thus, this work suggests a design procedure for noise-mitigation panel solutions and provides experimental proof of the versatility and effectiveness of labyrinthine metamaterials for tunable mid- to low-frequency sound attenuation.