Control of the acoustic waves in the subwavelength regime: metamaterials for perfect absorption and metadiffusers

Abstract

In the last decades, the exotic features of acoustic metamaterials have been deeply explored, but these special properties have been only recently extensively applied to audible sound in practical applications. The use of structured and locally-resonant media offers the possibility of tailoring their acoustic properties with a huge number of degrees of freedom (or with a huge freedom as you want), and, due to their resonant nature, their dimensions can be reduced to the subwavelength regime. This key feature has critical implications in the design of low frequency sound acoustic treatments, where the dimensions of the acoustic wavelength can exceed several meters. In this talk, different applications of structured materials with subwavelength dimensions are reviewed. First, we design absorbing panels for the reflection problems using arrays of Helmholtz resonators, showing that, using slow sound and the concept of critical coupling, perfect absorption can be obtained for panels almost one hundred thinner than the wavelength. Then, we show how using the same configuration, but allowing transmission, the problem of perfect absorption becomes more complex and we present several approaches to solve these issues. Solutions include transparent materials using the accumulation of resonances, symmetry-breaking and rainbow trapping metamaterials, where subwavelength perfect absorbers can be designed for a frequency band covering two octaves. Finally, we present the use of these resonant materials to tune the scattering of subwavelength thickness panels, showing the potential of structured materials for engineering acoustic applications in the audible regime.

@inproceedings{GrobyDENORMS2019,
 author = {Jean-Philippe Groby and Noé Jiménez and Weichn Huang and Vincent Pagneux and Vicent Romero-García and Trevor Cox},
 booktitle = {Industrial days on new acoustic treatments, acoustic metamaterials and sonic crystals. 6th DENORMS CA15125 Workshop. Athens, Greece. February 28th - March 1st},
 doi = {https://drive.google.com/open?id=1UvxrCRWiG3JPvitTt9g0DtiZC6xT3Rmd},
 editor = {Book of abstracts},
 month = {2},
 organization = {National Technical University of Athens},
 pages = {2},
 publisher = {COST Action Denorms},
 series = {Oral},
 title = {Control of the acoustic waves in the subwavelength regime: metamaterials for perfect absorption and metadiffusers},
 url = {https://denorms.eu/2019/01/08/workshop-6/},
 year = {2019}
}