Surface impedance measurements as a function of moisture content in porous glass beads

The effects of moisture content on the acoustic surface impedance of outdoor soil has received recent attention [A. J. Cramond and C. G. Don, J. Acoust. Soc. Am. 82, 293–301 (1987)]. This work indicated dramatic effects of moisture content. A measurement apparatus for measuring the moisture content in a synthetic soil (100-μm spherical glass beads) and the acoustic surface impedance is being constructed. The apparatus consists of a cylindrical soil column that attaches to the sample end of an impedance tube. The moisture content in the soil column can be varied by applying a suction to one end of the column where a porous plate is positioned. Water is caused to flow in and out of the soil column through the porous plate. The acoustic surface impedance is measured using a phase gradient technique. [Work supported by DOA.]