ASA 128th Meeting - Austin, Texas - 1994 Nov 28 .. Dec 02

2pPAb1. On the use of probe microphone and level difference measurements to characterize air-filled porous media.

Carl K. Frederickson

James M. Sabatier

Natl. Ctr. for Phys. Acoust., Univ. of Mississippi, Coliseum Dr., University, MS 38677

Air-filled porous media have been characterized acoustically using level difference measurements and an impedance model that depends on a pore-shape factor, porosity, tortuosity, and bulk flow resistance. Least-squares fitting of level difference spectra only allows two of the above parameters to be independently determined. Probe microphone measurements have been used to determine the propagation constant in both washed sand and glass beads. Values of tortuosity calculated from probe microphone measurements were used in the analysis of level difference data to determine porosity and bulk flow resistance. An average pore-shape factor is used in the analysis. For the unconsolidated porous media used, the effect of the pore-shape factor variation was within the error range of the measurement. The availability of both probe microphone and level difference data has also allowed for the comparison of porosity and flow resistance values calculated from each set of data. There are some discrepancies between the frequency dependence of the model and the probe microphone data. [Work supported by USDA.]