Absorption characteristics of large acoustic metasurfaces

TL;DR

This paper investigates how finite size effects, such as surface waves and meta-resonances, influence the absorption properties of large acoustic metasurfaces, challenging the infinite metasurface assumptions.

Contribution

It provides a detailed model of finite acoustic metasurfaces, incorporating geometric and dissipation effects, to analyze their unique absorption characteristics.

Findings

Finite metasurfaces exhibit different absorption features due to surface waves.

Meta-resonances cause standing-wave patterns affecting absorption.

Finite size effects are significant even in large metasurfaces.

Abstract

Metasurfaces formed of arrays of subwavelength resonators are often tuned to 'critically couple' with incident radiation, so that at resonance dissipative and radiative damping are balanced and absorption is maximised. Such design criteria are typically derived assuming an infinite metasurface, whereas the absorption characteristics of finite metasurfaces, even very large ones, can be markedly different in certain frequency intervals. This is due to the excitation of surface waves, intrinsic to resonant metasurfaces, and especially meta-resonances, namely collective resonances where the surface waves form standing-wave patterns over the planar metasurface domain. We illustrate this issue using a detailed model of a Helmholtz-type acoustic metasurface formed of cavity-neck pairs embedded into a rigid substrate, with geometric and dissipation effects included from first principles (R. Brand\~ao and O. Schnitzer, Wave Motion, 97 102583, 2020).