Ultrasonic measurements of particle retention by a porous medium

Ultrasound transmission and reflection are utilized to characterize the particle retention in depth of fluid-saturated porous samples under a flow of silt solution. The effect of the concentration of particles in the fluid is investigated via measurements of "comparison coefficients" which are the ratio of the Fourier transforms of the reflected (transmitted) signals before and after the particle flow. Numerical computations of the latter coefficients using Biot-Stoll's theory are compared to the experimental data. The frequential evolution of physical parameters such as bulk and shear moduli are sought. To this end, a gradient descent algorithm is utilized to minimize the differences between the experimental and calculated comparison coefficients. Several concentrations of suspended particles are investigated to check the validity of this inversion method and a good agreement between theory and experiments is observed.