Abstract
Perfect, broadband and asymmetric sound absorption is theoretically, numerically and experimentally reported by using subwavelength thickness panels in a transmission problem. The panels are composed of a periodic array of varying cross-section waveguides, each of them being loaded by an array of Helmholtz resonators (HRs) with graded dimensions. The low cut-off frequency of the absorption band is fixed by the resonance frequency of the deepest HR, that reduces drastically the transmission. The preceding HR is designed with a slightly higher resonance frequency with a geometry that allows the impedance matching to the surrounding medium. Therefore, reflection vanishes and the structure is critically coupled. This results in perfect sound absorption at a single frequency. We report perfect absorption at 300 Hz for a structure whose thickness is 40 times smaller than the wavelength. Moreover, this process is repeated by adding HRs to the waveguide, each of them with a higher resonance frequency than the preceding one. Using this frequency cascade effect, we report quasiperfect sound absorption over almost two frequency octaves ranging from 300 to 1000 Hz for a panel composed of 9 resonators with a total thickness of 11 cm, i.e., 10 times smaller than the wavelength at 300 Hz.
BibTeX citation
@inproceedings{JimenezRomero-GarciaPagneuxEtAl2017,
author = {Noé Jiménez and Vicent Romero-García and Vincent Pagneux and Jean Philippe Groby},
booktitle = {Industrial Applications of Acoustic Metamaterials. GdR META and COST Action DENORMS (CA15125) workshop. Marseille, France. 1st September},
editor = {Book of abstracts},
month = {9},
organization = {GdR META},
pages = {1-5},
publisher = {COST Action DENORMS},
series = {Oral},
title = {Rainbow trapping absorbers: Broadband and perfect absorption in subwavelenth panels},
url = {https://denorms.eu/author/denorms/},
year = {2017}
}