A Review of Acoustical Methods for Porous Material Characterisation

The purpose of this paper is to present and discuss a range of in-situ and laboratory methods can be used to measure the morphological characteristics of porous materials. In the case of foams and granular media used for noise control applications, the most common of these characteristics are pore size and its distribution, porosity, and pore connectivity. In the case of fibrous media, the most useful non-acoustical characteristics are the fibre size and packing density. In the case of outdoor surfaces such as gravel, sandy soils, and agricultural land, which can be partly saturated with water, it is of direct interest to measure the degree of water saturation hydraulic permeability and pore size gradient. In the case of materials with good physiochemical properties, it is of interest to determine their internal pore surface area, porosity, and pore size scales. In this paper, the existing and newly emerging acoustic characterisation methods are discussed in terms of their complexity, accuracy, and sample requirements. The application of these methods relate to traditional needs to measure and predict the in-situ performance of noise control elements and outdoor surfaces, to ensure the quality control during material manufacturing process and to be able to measure non-invasively the micro- and nano-structure of porous media which is used in catalytic filters, electric capacitors and for gas storage. Parts of this paper were presented at the 22nd International Congress on Sound and Vibration in Florence