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

2pPAb3. The influence of pore-size distributions on complex wave number in air-filled porous materials.

David W. Craig

Carl K. Frederickson

James M. Sabatier

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

Probe microphones have been developed to determine tortuosity and effective flow resistivity for air-filled porous materials, such as agricultural soils. They are used to measure complex wave number as a function of frequency. These data are then inverted using a single-pore-size capillary tube model for propagation in the material. However, the frequency dependence of the measured wave number in sand differs from the predictions of such single-scale models. It is shown that distributions of pore sizes can produce a similar dependence. By summing over pore sizes, wave number as a function of frequency is calculated for lognormal, fractal (power-law), and empirical distributions derived from porosimetry data. Results are also compared with Wilson's relaxation-matched fractal model [D. K. Wilson, J. Acoust. Soc. Am. 94, 1136--1135 (1993)]. [Work supported by USDA.]