Acoustical characterization of absorbing porous materials through transmission measurements in a free field

Various results are presented to experimentally validate the theoretical modeling of the acoustic radiation of a circular piston through a thin layer of porous absorbing material, as worked out by Amedin et al. [J. Acoust. Soc. Am. 98, 1757–1766 (1995)]. This theoretical modeling is subsequently exploited for the development of an acoustical characterization method for porous absorbing materials. The method is based on acoustical pressure measurements taken at two different positions in an open baffled tube radiating into the material to be characterized and at a given point above the material, and on an iterative process of numerical resolution. The reliability of the method is evaluated by means of numerical simulations and by comparisons using the two-layer method in an impedance tube [J. Acoust. Soc. Am. 74, 1577–1582 (1983)]. The preliminary tests show that the new method can be used to experimentally characterize the specific acoustic impedance and the propagation constant of porous absorbing materi...