Characterization of suspensions by ultrasonic reflection measurements

Abstract

The ultrasonic attenuation and the ultrasonic backscatter coefficient from suspensions are known to be correlated with the concentration of particles and the particle size distribution. However, for suspensions with a very low particle concentration (< 500 ppm) the effect of the particles on the attenuation or backscatter coefficient is in general not significant. In this paper a new ultrasonic technique is presented, which can be applied to characterize suspensions with a very low concentration of particles. The method is based on ultrasonic reflection from individual particles passing through a small measurement volume. Such a small volume is achieved by applying a focused transducer and windowing of the time signal. The amplitude of a received reflection depends on the position of the reflecting particle in the measurement volume and on the dimensions and shape of the particle. A forward analytical model describes the relations between the suspension properties (particle size distribution and particle concentration) and the measured histogram of amplitudes. The particle size distribution and concentration are obtained from the measurements via numerical inversion of the forward model. Results of measurements on a well-controlled suspension demonstrate the feasibility of this technique.