Sound propagation in capillary‐tube‐type porous media with much smaller pores in the capillary walls

Abstract

Sound propagation in gas‐filled, capillary‐tube‐type porous media was investigated. The capillary tubes were taken to be nominally straight with very small pores in the walls of the capillary tubes. The central assumptions (which are frequency dependent) are that the wall pore diameters are much less than the viscous penetration depth, and that the acoustic pressure in the main pore is only a function of the longitudinal direction. As a consequence of these assumptions, the excess temperature of the gas in the wall pores can be taken as negligible. Walls were taken to be rigid. Propagation constants and the characteristic impedance of such a media were computed. Application to ceramic samples having square capillary pores and porous walls is developed as a possible explanation for the anomalous tortuosity factor previously inferred for this material [Roh et al., J. Acoust. Soc. Am. Suppl. 1 87, S139 (1990)]. Comparison is made to the theory for sound propagation in ducts having finite impedance walls.