Ultrasonic characterization of porous absorbing materials: Inverse problem

Transient Acoustic Wave Propagation in Porous Media

“…Let us study the sensitivity [20] of porosity on the transmission operatorT(t).T a k i n gt h e derivative ofT(t) versus the porosity φ, we obtain:…”

“…A simulated transmitted signal was calculated from the equation (31). The input signal is given in figure 3 and its spectrum in Figure 4.…”

“…Solving the inverse problem, using the transmitted waves allowed the determination of the tortuosity and viscous and thermal characteristic lengths. Note that the ratio of two lengths was set at 3 [20][21][22][23]. Currently the only method for the separate determination of the two lengths is based on the saturation of the porous by two different fluids [24].…”

“…But for common air-saturated porous materials, the second reflection is very damped and its experimental detection is difficult. We solve the inverse problem [31] numerically by the least-squares method, using both reflected and transmitted experimental data. We determine simultaneously all the physical parameters intervening in the propagation.…”

“…Tests are performed using industrial plastic foams. Experimental and numerical results, and prospects are discussed [31].…”