ATTENUATION MEASUREMENTS OF ULTRASOUND IN A KAOLIN WATER SLURRY - A LINEAR-DEPENDENCE UPON FREQUENCY

The attenuation of ultrasound through a kaolin-water slurry was measur ed for frequencies ranging from 0.5 to 3.0 MHz. The maximum concentrat ion of the slurry was for a weight percentage of 44% (or a volume frac tion of 0.24). The goal of these measurements was to assess the feasib ility of using ultrasonic attenuation to determine the concentration o f a slurry of known composition. The measurements were obtained by con secutively adding kaolin to the slurry and measuring the attenuation a t each concentration. After reaching a maximum concentration a dilutio n technique was used, in which an amount of slurry was removed and wat er was added, to obtain the attenuation as a function of the concentra tion. The dilution technique was the more effective method to obtain c alibration data. These measurements were carried out using two transdu cers, having a center frequency of 2.25 MHz, separated by 0. 101 6 m ( 4.0 in.). The maximum attenuation measured in these experiments was ab out 100 Np/m, but the experimental apparatus has the capability of mea suring a larger attenuation if the distance between the two transducer s is decreased. For a given frequency, the data show that In V/V0 depe nds linearly upon the volume fraction ( V is the received voltage for the slurry and V0 is that obtained for water). This indicated that eac h particle acts independently in attenuating ultrasound. The data show ed that the attenuation is proportional to the frequency and to the vo lume fraction. The results demonstrated the feasibility of using atten uation measurements to determine slurry concentration. Several theoret ical models are discussed that describe the attenuation of ultrasound. The data obtained by several other researchers also show a linear dep endence of attenuation upon frequency.