Measurement of tortuosity and viscous characteristic length of double-layered porous absorbing materials with rigid frames via transmitted ultrasonic wave

Abstract

In this work, an indirect method is proposed for measuring simultaneously acoustic parameters describing the ultrasonic propagation in double-layered porous medium. The porous media consist of two slabs of homogeneous isotropic porous materials with a rigid frame. Each porous slab is described by equivalent fluid model, in which the acoustic wave propagates only in the fluid saturating the material. The inverse problem is solved numerically using experimental transmitted waves in time domain. Four parameters are inverted: tortuosity and viscous characteristic lengths of the two layers. Tests are performed using industrial plastic foams. Experimental and numerical validation results of this method are presented.