Experimental characterization of rigid porous material via the first ultrasonic reflected waves at oblique incidence

Enhanced ultrasonic method for the evaluation of acoustic parameters of air-saturated porous material is presented. This method is based on the direct and inverse problem of the reflection of an oblique incident wave from the surface of the porous medium with rigid frame. The interaction of the sound pulse with the porous material is described by the equivalent fluid model using the Johnson-Champoux-Allard approach (JCA) to describe the visco-inertial dissipative effects and the thermal effects inside the porous media. Four parameters are involved in the calculation of the dynamic density and the bulk modulus at high frequencies, namely the porosity ϕ, the high frequency limit of tortuosity α∞, the viscous and thermal characteristic lengths Λ and Λ′. The sensitivity of each parameter on reflected waves from the surface of the porous medium is studied for different oblique angles of incidence. The advantage of the proposed method is that the inverted values of porosity, tortuosity, viscous and thermal characteristic lengths are simultaneously obtained by minimizing between the experimental and simulated reflected signals. Moreover, no relationship is assumed between the viscous and thermal characteristic lengths. The numerical and experimental validation of this method is presented and compared to the theoretical prediction.