Ultrasonic velocity and attenuation in models of dry and wet sands with an embedded object

Abstract

Propagation of ultrasound in wet and dry sand, up to 6 in. in depth, is investigated. Velocity and attenuation, as a function of mean grain size, water content, and depth, are measured. The results can be used in the detection of the objects embedded in dry and wet sand. Experiments show that for a dry sand, at frequencies of the order of 500 kHz and above, no through-transmitted signal is detectable. This is due to a very strong attenuation, even for a sample having only a depth of 2 in. However, in a wet sand sample, attenuation is significantly smaller, therefore strong signal is detected at a depth of 6 in. Using low-frequency transducers it is possible to transmit and receive longitudinal ultrasonic pulses in dry sand model medium, for depths of up to several inches. Some application of these results to the detection of objects embedded at a shallow depth of the order of several inches will be discussed.