Attenuation measurements of ultrasound in a kaolin–water slurry: A linear dependence upon frequency

Abstract

The attenuation of ultrasound through a kaolin–water slurry was measured for frequencies ranging from 0.5 to 3.0 MHz. The maximum concentration of the slurry was for a weight percentage of 44% (or a volume fraction of 0.24). The goal of these measurements was to assess the feasibility of using ultrasonic attenuation to determine the concentration of a slurry of known composition. The measurements were obtained by consecutively adding kaolin to the slurry and measuring the attenuation at each concentration. After reaching a maximum concentration a dilution technique was used, in which an amount of slurry was removed and water was added, to obtain the attenuation as a function of the concentration. The dilution technique was the more effective method to obtain calibration data. These measurements were carried out using two transducers, having a center frequency of 2.25 MHz, separated by 0.1016 m (4.0 in.). The maximum attenuation measured in these experiments was about 100 Np/m, but the experimental apparatus has the capability of measuring a larger attenuation if the distance between the two transducers is decreased. For a given frequency, the data show that ln V/V0 depends linearly upon the volume fraction (V is the received voltage for the slurry and V0 is that obtained for water). This indicated that each particle acts independently in attenuating ultrasound. The data showed that the attenuation is proportional to the frequency and to the volume fraction. The results demonstrated the feasibility of using attenuation measurements to determine slurry concentration. Several theoretical models are discussed that describe the attenuation of ultrasound. The data obtained by several other researchers also show a linear dependence of attenuation upon frequency.