Acoustic characterization of rigid-frame air-filled porous media using both reflection and transmission measurements

Abstract

Acoustic measurements in and above porous materials (500-μm-diam glass beads) have been used to determine rigid-frame porous medium parameters. The propagation constant for the acoustic signal propagating through the air in the pores was calculated from probe microphone measurements made inside the porous medium. Reflection measurements have been used to calculate the characteristic impedance of a thick porous medium. A model relating porous medium properties to the propagation constant and impedance was used to analyze the data from both the reflection and transmission measurements. Both reflection and transmission measurements are needed to determine the rigid-frame porous medium parameters. Porous medium parameters can be calculated using the model and the data. The calculated porous medium parameters from the transmission and reflection measurements are compared. Some possible explanations for the discrepancy and suggestions for further work are presented.