Beyond phase grating diffusers using locally-resonant metamaterials

Abstract

We present sound diffusers based on locally resonant metamaterials that are one order magnitude thinner than the classical designs based on phase gratings. Using a set of waveguides loaded by an array of optimized Helmholtz resonators, we induce strong dispersive propagation inside the material. Doing this, waves in the low-frequency regime are almost frozen and, because of this, a deep-subwavelength resonance is produced. In addition, this design allows an accurate tuning of the thermoviscous loses. In this way, the reflection coefficient can be spatially tuned in both phase and magnitude, and we are able to mimic the classical QRD, PRD or Binary/Ternary sound diffusers. Beyond these designs, we also propose an optimized panel showing efficient and broadband sound diffusion ranging from 250 Hz to 2 kHz using only 3 cm thickness, i.e., 46 times thinner than the wavelength at the lowest working frequency.

@inproceedings{ICAjimenez2019,
 author = {Noé Jiménez and Trevor Cox and Jean Philippe Groby and Vicente Romero-García},
 booktitle = {ICA 2019: 23rd International Congress on Acoustics. Aachen, Germany. 9-13 September},
 doi = {http://doi.org/10.18154/RWTH-CONV-239375},
 editor = {Proceedings of the 23rd International Congress on Acoustics},
 isbn = {ISBN: 978-84-87985-30-4},
 month = {9},
 organization = {International Commission for Acoustics},
 pages = {2270-2277},
 publisher = {German Acoustical Society},
 series = {Invited},
 title = {Beyond phase grating diffusers using locally-resonant metamaterials},
 url = {https://publications.rwth-aachen.de/record/769786/files/769786.pdf},
 year = {2019}
}