Acoustic radiation of a vibrating wall covered by a porous layer: Transfer impedance concept and effect of compression.

Abstract

The acoustic radiation of a vibrating wall covered by a porous layer is investigated. The porous layer is described by the one-dimensional Biot model: it accounts for the propagation of the two longitudinal waves in the porous layer within its thickness. The transfer impedance concept [Doutres et al., J. Acoust. Soc. Am. 121, 206–213 (2007)] allows to determine the effect of the porous layer on the acoustic radiation of the vibrating wall. This impedance differs from the surface impedance that can be measured in a plane wave impedance tube. It is shown that the radiation efficiency of the structure increases in the vicinity of the first resonance of the skeleton in its thickness and decreases for higher frequencies. Experimental validation is performed with a baffled piston covered by a foam or a fibrous layer. Only the radiation model using the transfer impedance shows close agreement with experimental data. Finally, effect of compression of the porous layer is investigated by both analytical and experimental approaches, in the case of fibrous materials used in aeronautical applications.