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This paper presents a case study on the full inverse characterization of the material properties of an open-cell poroelastic foam using impedance tube measurements. It aims to show the importance of controlling the lateral boundary condition in the impedance tube, and selecting an appropriate acoustic model to obtain the most accurate material properties. The case study uses a four-inch thick melamine foam and a 100-mm diameter tube. The foam is mechanically cut to fit within the circular tube. However, the cutting process is not perfect and a tiny lateral air gap exists between the material and the tube (i.e. the foam diameter is 99.5 mm for a 100-mm diameter tube). The typical characterization procedure is to mix direct and indirect measurements to retrieve the material properties of the foam. First, open porosity, bulk density, and static airflow resistivity are directly measured.

A poroelastic characterization of open-cell porous materials using an impedance tube is proposed in this paper. Commonly, porous materials are modeled using Biot’s theory. However, this theory requires several parameters which can be difficult to obtain by different methods (direct, indirect or inverse measurements). The proposed method retrieves all the Biot’s parameters with one absorption measurement in an impedance tube for isotropic poroelastic materials following the Johnson-Champoux-Allard’s model (for the fluid phase). The sample is a cylinder bonded to the rigid termination of the tube with a diameter smaller than the tube’s one. In that case, a lateral air gap is voluntary induced to prevent lateral clamping. Using this setup, the absorption curve exhibits a characteristic elastic resonance (quarter wavelength resonance) and the repeatability is ensured by controlling boundary and mounting conditions.