Overview of the porous material characterization methods and impedance tube measurements, by Raymond Panneton (University of Sherbrooke) [Dec. 4, 2017]
DENORMS Action's Training School "Experimental techniques for acoustic porous materials and metamaterials", Le Mans, 4-6th December 2017
Lecturer: Raymond Panneton (University of Sherbrooke)
This course will present direct and inverse methods, standards, and tools for the characterization of the acoustical and non-acoustical properties of acoustic porous materials. It will present the main challenges related to their characterization and guidelines to ensure their fine characterization. It will also address solutions to recurrent problems observed during characterization in relation with acoustical leaks, frame vibrations, boundary conditions, variations of environmental conditions, badly shaped samples, mounting of the samples, and non-symmetry and non-homogeneity of the samples. Examples of the characterization of different porous media (foams, fibers, felts, films) with rigid-frame, limp-frame, and elastic-frame behaviors will be presented. The acoustical properties covered in this course are the normal incidence sound absorption coefficient, sound transmission loss, surface and characteristic acoustic impedance, complex wave number, dynamic density and bulk modulus, and transfer matrices. The non-acoustical properties are notably the open porosity, static airflow resistivity or permeability, tortuosity, viscous and thermal characteristic lengths, static thermal permeability, and bulk density. While the acoustical properties are obtained with acoustical impedance/transmission tubes, the non-acoustical properties are obtained by direct methods and by inverse methods based on impedance/transmission tube measurements.