Acoustic characterization of air-saturated porous materials by solving the inverse problem.

We present in this contribution, several experimental methods for the acoustic characterization of air-saturated porous materials. The equivalent fluid model is considered, in which the acoustic wave propagates in the saturating fluid of the porous material. The principle of these methods is the detection of experimental waves reflected and transmitted by the porous material. The high and low frequency domains are studied. The sensitivity of the non-acoustic parameters - porosity, tortuosity, viscous and thermal characteristic lengths, viscous and thermal permeabilities is studied, showing their effects on the transmitted and reflected waveforms. It is shown that some parameters are more sensitive to the transmission mode, and others to the reflection. The inverse problem is solved numerically using experimental data of waveforms in the time domain for these parameters. Tests are performed using industrial plastic foams. The inverted values of non-acoustic parameters are close to those measured by classical methods. The results of the experimental and numerical validation of this method are presented and compared with theoretical predictions and a very good agreement has been found.