Experimental characterization of fully-anisotropic equivalent fluids from normal incidence measurements

Experimental validation remains crucial in the fields of acoustics materials and meta-materials. This study is based on a recent method, built upon the theoretical framework introduced by Terroir et al. in 2019, for characterizing three-dimensional anisotropic equivalent fluids, to which the experimental validation is paramount. This work focuses on the characterization of anisotropic fluids using a limited set of acoustic measurements in an impedance tube. In addition, the method demonstrates its ability to recover the Johnson–Champoux–Allard–Lafarge (JCAL) parameters as well as rotation angles and principal directions of an unknown equivalent fluid. These parameters are meaningful in understanding the acoustics of anisotropic porous materials. The recovery of these parameters is performed by a minimization procedure, which first recovers the thermo-acoustic properties of the medium, and secondly its visco-inertial properties. This technique showcases promise in effectively characterizing complex porous materials, underlining its potential for practical application.