Acoustic Wave Propagation in Multiscale Sorptive Porous Materials

Orateur : Rodolfo VENEGAS (Acoustics Research Centre, University of Salford, United Kingdom)

The microstructure of multiscale sorptive porous materials features pores or inclusions of very different characteristic sizes ranging from nanometres to millimetres. We investigate acoustic wave propagation in multiscale rigid-frame porous materials that support sorption and different types of diffusion in addition to the usual visco-thermo-inertial interactions. We make successive use of the two-scale asymptotic method of homogenization to derive effective equations that describe sound propagation through the material macroscopically. This allows us to conclude that the macroscopic mass balance is significantly modified by sorption and inter-scale mass and pressure diffusion. This modification is accounted for by the dynamic compressibility of the effective saturating fluid which presents atypical properties that lead to slower speed of sound and higher sound attenuation, particularly at low frequencies. We validate the theory by comparing the predictions of an analytical model with experimental data for activated carbons and provide evidence supporting a measurement method for sorption and mass diffusion properties using sound waves. Applications of multiscale sorptive porous materials to loudspeakers, acoustic resonators, wall partitions, and gas springs will also be presented.

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