Experimental validation of deep-subwavelength diffusion by acoustic metadiffusers

TLDR

Acoustic metadiffusers are subwavelength resonant surfaces that exploit slow sound propagation. This study experimentally validates a quadratic‑residue acoustic metadiffuser by measuring its scattering response. The device uses rigidly backed slotted panels whose slits are loaded with arrays of Helmholtz resonators. The metadiffuser achieves a dramatically reduced effective thickness compared to conventional quarter‑wavelength diffusers, and experimental measurements agree with theory, demonstrating its capability to control low‑frequency sound diffusion.

Abstract

An acoustic metadiffuser is a subwavelength locally resonant surface relying on slow sound propagation. Its design consists of rigidly backed slotted panels, with each slit being loaded by an array of Helmholtz resonators. Due to the slow sound properties, the effective thickness of the panel can therefore be dramatically reduced when compared to traditional diffusers made of quarter-wavelength resonators. The aim of this work is to experimentally validate the concept of metadiffusers from the scattering measurements of a specific metadiffuser design, i.e., a quadratic residue metadiffuser. The experimental results reported herein are in close agreement with analytical and numerical predictions, therefore showing the potential of metadiffusers for controlling sound diffusion at very low frequencies.