The influence of microstructure on propagation in porous fibrous absorbents

Abstract Parameters commonly used to describe the dependence of wave propagation in porous materials on their microstructure derive from a conceptual model of an ideal capillary pore medium. The theories which introduce these parameters are reviewed, and their limitations, when applied to propagation in flexible, fibrous media, are discussed. Alternative models and associated analyses which define the disposition of the solid rather than that of the fluid are considered. In particular, a scattering analysis, which has previously been applied to a simple model of parallel, identical fibres in air, is introduced. This approach is extended in order to deduce bulk acoustical parameters for more realistic versions of the fibre model. The theoretically predicted effects of (i) variation in fibre flexibility, (ii) distributions of fibre radii, (iii) shot content, and (iv) fibre orientation, are considered.

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