Ultrasonic measurement of the porosity and tortuosity of air-saturated random packings of beads

In the pore space of packed grain material, transport properties are characterized by macroscopic parameters. Some of them, porosity and tortuosity, are measured for random packing of glass beads and compared with evaluations made during previous studies. A simple method for measuring porosity and tortuosity for air-saturated granular media is given. This method is based on a temporal model of the direct and inverse scattering problem for the propagation of transient ultrasonic waves in a homogeneous isotropic slab of porous material with a rigid frame. Viscous and thermal losses of the medium are described by temporal operators describing memory effects in a porous medium. Because of the high attenuation of acoustic waves in air-saturated packings of beads, the wave reflected by this medium is equivalent to the wave reflected by the first interface. Using this approximation, a simple relation between porosity, tortuosity, the angle of incidence, and the reflected wave is obtained. Porosity and tortuosity are thus measured via reflected waves in the porous medium at oblique incidence. Experimental and numerical validation results for this method are given for a sample of random packings of glass beads. (C) 2003 American Institute of Physics.