Spider web-structured labyrinthine acoustic metamaterials for low-frequency sound control

A O Krushynska,N M Pugno,M Miniaci,F Bosia

doi:10.1088/1367-2630/aa83f3

Abstract

Attenuating low-frequency sound remains a challenge, despite many advances in this field. Recently-developed acoustic metamaterials are characterized by unusual wave manipulation abilities that make them ideal candidates for efficient subwavelength sound control. In particular, labyrinthine acoustic metamaterials exhibit extremely high wave reflectivity, conical dispersion, and multiple artificial resonant modes originating from the specifically-designed topological architectures. These features enable broadband sound attenuation, negative refraction, acoustic cloaking and other peculiar effects. However, hybrid and/or tunable metamaterial performance implying enhanced wave reflection and simultaneous presence of conical dispersion at desired frequencies has not been reported so far. In this paper, we propose a new type of labyrinthine acoustic metamaterials (LAMMs) with hybrid dispersion characteristics by exploiting spider web-structured configurations. The developed design approach consists in adding a square surrounding frame to sectorial circular-shaped labyrinthine channels described in previous publications (e.g. ()). Despite its simplicity, this approach provides tunability in the metamaterial functionality, such as the activation/elimination of subwavelength band gaps and negative group-velocity modes by increasing/decreasing the edge cavity dimensions. Since these cavities can be treated as extensions of variable-width internal channels, it becomes possible to exploit geometrical features, such as channel width, to shift the band gap position and size to desired frequencies. Time transient simulations demonstrate the effectiveness of the proposed metastructures for wave manipulation in terms of transmission or reflection coefficients, amplitude attenuation and time delay at subwavelength frequencies. The obtained results can be important for practical applications of LAMMs such as lightweight acoustic barriers with enhanced broadband wave-reflecting performances.

Highlights

Manipulating low-frequency sound remains a challenging task for scientists and engineers, despite a vast amount of research in this field
We have proposed labyrinthine metamaterials with hybrid properties with respect to those analyzed in the literature far, with attractive properties for low-frequency sound-wave manipulation, drawing inspiration from the architecture of a spider web
The key advantage of this design is the versatility in controlling wave manipulation performance, e.g. activation/removal of band gaps by changing the unit cell topological organization, such as the number and width of the curved channels, as well as by introducing cavities externally at the unit cell corners or internally between the channels

Summary

Introduction

Manipulating low-frequency sound remains a challenging task for scientists and engineers, despite a vast amount of research in this field. Acoustic metamaterials are engineered composites with unusual effective characteristics, e.g. negative bulk modulus and/or mass density, zero or negative effective refractive index, etc These metamaterials can formally be divided into locally resonant metamaterials with basic units incorporating resonators [2, 3] and other metastructures described by effective medium theories [4, 5, 6]. The latter comprise so-called “labyrinthine” or “space coiling” metamaterials with a geometry-based mechanism for controlling subwavelength acoustic waves [7, 8, 9, 10, 11]

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