Scattering of ultrasound by emulsions

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Abstract
Ultrasonic scattering theory is used to relate the ultrasonic velocity and attenuation of emulsions to their physical properties (e.g. droplet size and volume fraction). This theory includes visco-inertial and thermal scattering mechanisms and corrections due to multiple scattering. The physical significance of the scattering mechanisms is discussed so as to highlight the factors which influence ultrasonic measurements in these systems. Theoretical predictions were compared with experimental measurements of velocity and attenuation in sunflower oil in water emulsions with varying droplet radii (0.14-0.74 mu m), mass fraction (0-0.5) and frequency (1.25-10.0 MHz) at 293.1 K. Appreciable excess attenuation and velocity dispersion were observed which could be attributed to thermal scattering. The relationship between the measurable ultrasonic parameters and the physical properties of emulsions means ultrasonic scattering should prove a useful means of investigating these systems.
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