C. Maury and T. Bravo
FORUM ACUSTICUM 2020, FA2020/35,
E-congress celebrado del 7 al 11 de diciembre de 2020, Lyon, Francia.
Theoretical, numerical and experimental studies are presented that investigate the wideband absorption properties of unbacked and rigidly-backed microcapillary plates (MCPs) under normal plane wave incidence. MCPs are characterized by a perforation ratio greater than 50 % and channels diameters between 4μm and 50μm, thus leading to a thin porous absorber with a regular distribution of at most one million of microchannels per cm2. They are fabricated by micro-chemical etching process. Unlike micro-perforated panels, the MCPs have a high perforation ratio that ensures minute reactance, thereby reducing their transfer impedance to a pure resistance over a broad frequency range. Moreover, their micrometric channels diameter allows tailoring their resistance to achieve constant target absorption over a wide frequency band. This property has been validated through finite-element simulations that also confirmed isothermal conditions in capillary channels. An optimal value of the micro-channels diameter can be derived that achieves maximal viscous dissipation of the acoustical energy under plane wave anechoic load. Kundt tube experiments confirmed the ability of optimized MCPs to achieve wideband flat absorption performance that exceeds 0.85 up to a Helmholtz number of 0.3. They also showed the potential of non-optimal acousticallytransparent MCPs to achieve a low-frequency anechoic termination.
ACKNOWLEGMENTS
This study was funded in Spain by the Ministerio de Economía y Competitividad project TRA2017-87978-R, AEI/FEDER, UE, and the mobility program ILINK+2018. It was supported in France by the ANR VIRTECH (ANR-17-CE10-0012-01). The authors would like to thank J. Kergomard, Emeritus Director of Research at CNRS-LMA, for fruitful discussions, Dr. P. Ecker from GIDS GmbH for kindly borrowing us one of the MCPs and Dr. L. Sabatier, Research Engineer at CNRS-LMA, for X-ray imaging the MCPs.
