Transport parameters for sound propagation in air saturated motionless porous materials: A review

Transport parameters play a key role in characterizing the thermo-viscous behaviour of the microgeometry. Semi-phenomenological models provide valuable tools to establish a connection between the dynamic behaviour of porous materials and these transport parameters. However, each model has its limitations in terms of the frequency range and material types it can accurately represent. One of the most used semi-phenomenological acoustic models in the literature is the Johnson-Champoux-Allard-Lafarge (JCAL) model [J. Fluid. Mech. 176 (1987) 379–402, J. App. Phy. 70 (1998) 1975, J. Ac. Soc. Am. 102 (1998) 1995]. This model requires the knowledge of six transport parameters, known as the porosity φ, airflow resistivity σ, thermal characteristic length Λ′, viscous characteristic length Λ, high-frequency limit of tortuosity α∞, and static thermal permeability k0′, which establish a connection between the micro-geometrical features of the porous material and its macroscopic behaviour when subjected to sound waves. The JCAL model is applicable to all types of porous materials, and the required transport parameters can be measured using suitable devices. With recent advancements in additive manufacturing, it is now possible to create porous materials with precise and controlled geometries. Therefore, understanding the relationships between microgeometry and transport parameters is crucial for designing porous materials with specific acoustic properties. This study provides a comprehensive overview of all the transport parameters involved in characterizing the JCAL model. It synthesizes various direct, indirect, and inverse measurement techniques used to assess these parameters. Additionally, computational approaches for evaluating the transport parameters from representative elementary volumes (REV) of materials are presented. Finally, the study compiles the existing correlations between transport parameters and the microgeometry of the unit cell from the available literature.