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

TL;DR

This study shows that visco-thermal effects critically influence acoustic metamaterials, causing a shift from total transmission to total reflection and high absorption, which is essential for realistic modeling of their behavior.

Contribution

The paper provides the first combined theoretical and experimental analysis of visco-thermal effects in acoustic metamaterials, highlighting their dominant role in acoustic response.

Findings

Visco-thermal losses prevent Fabry-Perot resonances in narrow slits.

Complete reflection occurs due to these losses, opposite to ideal lossless predictions.

Energy dissipation can reach up to 50% at optimal slit widths.

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 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.