Ultra-thin metamaterial for perfect and omnidirectional sound absorption

TL;DR

This work introduces an ultra-thin acoustic metamaterial panel that achieves perfect, omnidirectional sound absorption by leveraging slow sound and critical coupling, with theoretical and experimental validation.

Contribution

It presents a novel design of a metamaterial panel with Helmholtz Resonators that enables perfect sound absorption at deep sub-wavelength scales, both theoretically and experimentally.

Findings

Achieves perfect sound absorption across various angles.

Operates at deep sub-wavelength scale ($rac{rac{1}{88}}$).

Demonstrates tunable absorption via geometry and losses.

Abstract

Using the concepts of slow sound and of critical coupling, an ultra-thin acoustic metamaterial panel for perfect and omnidirectional absorption is theoretically and experimentally conceived in this work. The system is made of a rigid panel with a periodic distribution of thin closed slits, the upper wall of which is loaded by Helmholtz Resonators (HRs). The presence of resonators produces a slow sound propagation shifting the resonance frequency of the slit to the deep sub-wavelength regime ($\lambda/88$). By controlling the geometry of the slit and the HRs, the intrinsic visco-thermal losses can be tuned in order to exactly compensate the energy leakage of the system and fulfill the critical coupling condition to create the perfect absorption of sound in a large range of incidence angles due to the deep subwavelength behavior.