Inversion Problems for Determining Physical Parameters of Porous Materials: Overview and Comparison Between Different Methods

In modeling the acoustical behavior of porous materials, the determination of the physical parameters (that are airflow resistivity, open porosity, tortuosity and viscous and thermal characteristic lengths) is a fundamental issue. As an alternative to measuring some of these quantities directly, it is possible to use inverse strategies to calculate them once some of the acoustical parameters are experimentally known. In this work both analytical and minimization-based methods will be investigated to determine the physical parameters of porous materials. Among the analytical approaches (that are derived from dynamic density and bulk modulus expressions governing viscous and thermal dissipation of sound waves in rigid-framed porous media), several formulae have been proposed in literature and some will also be considered in the proposed analysis. In this paper only the procedures that are able to provide a complete set of physical data from acoustical tests will be investigated. The results will be compared with theoretical and experimental data and details related to the accuracy and reliability of the inversely determined parameters will also be reported and discussed. © S. Hirzel Verlag.