A WIDE-BANDWIDTH ULTRASONIC STUDY OF SUSPENSIONS - THE VARIATION OF VELOCITY AND ATTENUATION WITH PARTICLE-SIZE

Wide-bandwidth measurements of ultrasonic velocity and attenuation hav e been made in a series of monodisperse suspensions of polystyrene in water and silica in water. Suspensions with three different particle s izes at fixed volume fractions were used in each case. The results ena ble comparison between theory and experiment of the variation in phase velocity and attenuation with frequency and with particle size. It is shown that there is good agreement between the attenuation results an d the Allegra and Hawley theoretical model for both types of suspensio n investigated. However, in the case of the polystyrene suspensions, m easured phase velocity as a function of frequency does not follow the expected R root f dependence, although the form of the measured disper sion curve is close to theoretical. Reasons for the discrepancies betw een the model and the experimental data are suggested, and it is concl uded that the Allegra and Hawley formulation could form the basis of a particle sizing technique, provided that attenuation and velocity mea surements were made over a broad, and continuous, frequency band. (C) 1994 Academic Press, Inc.