SLOW-WAVE PROPAGATION IN AIR-FILLED POROUS MATERIALS AND NATURAL ROCKS

Slow compressional waves in fluid-saturated porous solids offer a unique acoustical means to study certain material properties, such as tortuosity and permeability. We present a novel experimental technique based on the transmission of airborne ultrasound through air-filled porous samples. The suggested method can be used to measure the velocity and attenuation of the slow compressional wave in a wide frequency range from 30 to 500 kHz. More important, the technique is so sensitive that it provides irrefutable evidence of slow wave propagation in air-saturated natural rocks and lends itself quite easily to tortuosity measurements in such materials, too.