Subwavelength absorbers and metasurfaces, Plenary Lecture by Noé Jiménez (Laboratoire d’Acoustique de l’Université du Maine, UMR 6613 CNRS)

DENORMS Action’s Workshop “Modelling of high performance acoustic structures Porous media, metamaterials and sonic crystals”, Rome, 24-25th January 2017

Website of DENORMS Action

Programme of the Workshop

Acoustic metamaterials (i.e. subwavelength absorbers), metasurfaces and sonic crystals for audible sound manipulation

Speaker: Noé Jiménez (Laboratoire d’Acoustique de l’Université du Maine, UMR 6613 CNRS)

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.