Visco-thermal effects in acoustic metamaterials: from total transmission to total reflection and high absorption

Miguel Molerón,Marc Serra-Garcia,Chiara Daraio

doi:10.1088/1367-2630/18/3/033003

Miguel Molerón, Marc Serra-Garcia + Show 1 more

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https://doi.org/10.1088/1367-2630/18/3/033003

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Abstract

We theoretically and experimentally investigate visco–thermal effects on the acoustic propagation through metamaterials consisting of rigid slabs with subwavelength slits embedded in air. We demonstrate that this unavoidable loss mechanism is not merely a refinement, but that it plays a dominant role in the actual acoustic response of the structure. Specifically, in the case of very narrow slits, the visco–thermal losses avoid completely the excitation of Fabry–Perot resonances, leading to 100% reflection. This is exactly opposite to the perfect transmission predicted in the idealised lossless case. Moreover, for a wide range of geometrical parameters, there exists an optimum slit width at which the energy dissipated in the structure can be as high as 50%. This work provides a clear evidence that visco–thermal effects are necessary to describe realistically the acoustic response of locally resonant metamaterials.

Highlights

Metamaterials are artificial structured materials in which the presence of resonances in the micro/meso-scale leads to unprecedented properties [1, 2]
Metamaterials consisting of rigid slabs with subwavelength perforations have attracted considerable attention due to their ability to achieve normalised-to-area transmission significantly bigger than unity, a phenomenon known as extraordinary acoustic transmission (EAT) [3]
When visco–thermal effects are included in the model, we observe a strong attenuation of the resonance peaks as Leff increases, which is in good agreement with the experimental results

Summary

Introduction

Metamaterials are artificial structured materials in which the presence of resonances in the micro/meso-scale leads to unprecedented properties [1, 2]. Metamaterials consisting of rigid slabs with subwavelength perforations have attracted considerable attention due to their ability to achieve normalised-to-area transmission (i.e., transmission normalised to the fraction of area occupied by the holes) significantly bigger than unity, a phenomenon known as extraordinary acoustic transmission (EAT) [3] This phenomenon, analogue to extraordinary optical transmission [4], can be achieved by means of different physical mechanisms, such as the excitation of Fabry–Perot (FP) resonances in the holes [3, 5,6,7], the acoustic Brewster angle [8, 9], or the acoustic analog to the supercoupling effect in density–near–zero metamaterials [10]. Visco–thermal dissipation in microslits has been used to enhance the attenuation of metamaterials [21], and important boundary layer effects have been reported in phononic crystals [22, 23]

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