Abstract
Broadband, perfect and asymmetric sound absorption is theoretically, numerically and experimentally reported in this work by using subwavelength thickness panels with transmission. 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. This process can be repeated by adding additional HR to the waveguide, each of them with a higher resonance frequency than the preceding one. Using this frequency cascade effect, we report quasi-perfect sound absorption over almost two frequency octaves ranging from 300 to 1000 Hz for a transparent panel composed of 9 resonators with a total thickness of 11 cm, i.e., 10 times smaller than the wavelength at 300 Hz. In the case of a subwavelength asymmetric panel, we report monochromatic perfect absorption at 300 Hz for a structure whose thickness is 40 times smaller than the working wavelength.
BibTeX citation
@article{JimenezSciReps2017,
author = {Noé Jiménez and Vicent Romero-García and Vincent Pagneux and Jean-Philippe Groby},
doi = {https://doi.org/10.1038/s41598-017-13706-4},
issn = {2045-2322},
journal = {Scientific Reports},
month = {10},
pages = {13595},
title = {Rainbow-trapping absorbers: Broadband, perfect and asymmetric sound absorption by subwavelength panels for transmission problems},
url = {https://www.nature.com/articles/s41598-017-13706-4.pdf},
volume = {7},
year = {2017}
}