@article {Costa Baptista:2021:0736-2935:2219,
title = "Multilayer treatment for subwavelength and broad absorption",
journal = "INTER-NOISE and NOISE-CON Congress and Conference Proceedings",
parent_itemid = "infobike://ince/incecp",
publishercode ="ince",
year = "2021",
volume = "263",
number = "4",
publication date ="2021-08-01T00:00:00",
pages = "2219-2227",
itemtype = "ARTICLE",
issn = "0736-2935",
url = "https://ince.publisher.ingentaconnect.com/content/ince/incecp/2021/00000263/00000004/art00029",
doi = "doi:10.3397/IN-2021-2076",
author = "Costa Baptista, Josu{\’e} and Roland-Fotsing, Edith and Mardjano, Jacky and Therriault, Daniel and Ross, Annie",
abstract = "Single layer optimized microchannels (268\textmum channels size) present high absorption at the quarter-wave resonance frequency (2460Hz for 30mm-thick treatment) but cannot provide significant absorption at lower frequencies. In this work, the absorption coefficient of multilayer treatments
with 2, 5, 10- and 30-layers of channels with size varying from 50\textmum to 15mm was numerically optimized. The equivalent fluid wave number and characteristic impedance of each layer were predicted using the JCAL model. The Double-scale Asymptotic Method (DAM) was used to obtain the JCAL
parameters. The multilayer treatment absorption was modelled with the Transfer Matrix Method (TMM). It was shown that multilayer treatments present superior absorption than single layer. For instance, bilayer treatment made of a 1mm-thick top layer (facing incident wave) of channels of 58\textmum
and a 29mm-thick bottom layer of channels with 8.1mm provides perfect absorption around 1200Hz (i.e. 1260Hz below the quarter-wave resonance frequency of 30mm-thick single layer treatment). Alternatively, a 30-layer treatment with channels size varying from 100\textmum to 9.6mm provides absorption
higher than 0.8 between 1350 and 6270Hz (i.e. 54% higher than single layer treatment with same thickness). These results pave the way to the fabrication of new multilayer treatments with interesting subwavelength and broadband absorption capabilities.",
}