Obtaining Poroelastic Parameters of Porous Materials from Impedance Tube Measurements

The accurate characterization of the acoustic and elastic parameters of a porous material based on impedance tube measurements presents challenges, in particular, because the specimens’ diameters can deviate from the nominal inner diameter of the impedance tube. If the specimen’s diameter exceeds the nominal diameter of the tube, it is compressed and therefore the material parameters are modified. The elastic solid phase of the diphasic poroelastic material is modelled using Biot’s model with the parameters mass density, Young’s modulus, Poisson’s ratio, and loss factor. In the fluid phase, viscous and thermal dissipation is modeled with the JCAL model which uses the parameters static airflow resistivity, open porosity, tortuosity, static thermal permeability, and viscous and thermal characteristic lengths. The model is restricted to plane waves at normal incidence, enabling an analytical coupling of the two models. In this contribution, the parameters of the diphasic poroelastic Biot-JCAL model are fitted to impedance tube measurements of the FOAM 02-database. This database contains 864 measurements of the sound absorption coefficient obtained in an impedance tube with±2% diameter deviation. An inverse parameter characterisation model is implemented in Python. The results highlight the effect of diameter inaccuracies on the visco-thermal and elastic parameters of the Biot-JCAL model.