Sensitivity study of the acoustic parameters on the wave transmitted through a bilayer porous medium at very low frequencies

The objective of this work is to present a sensitivity study of very low frequency parameters on waves transmitted through a bilayer medium made of two different layers of a porous medium saturated with air. The equivalent fluid theory is considered. Viscous-inertial and thermal effects are taken into account by the dynamic tortuosity and dynamic compressibility given by the Johnson-Champoux-Allard (JCA) model. At very low frequencies, the dynamic tortuosity and compressibility depend only on the porosity and air flow resistivity. An expression of the transmission coefficient of a bilayer medium has been established in the frequency regime. This expression depends on the porosity and resistivity of each layer. The influence of the ±20% variation in these parameters on the transmitted signal was presented and discussed. This study was done in the frequency domain as well as in the time domain.