Ultrasonic spectroscopy study of salad dressings

Ultrasonic velocity and attenuation spectra (1 to 100 MHz) of salad dressin gs with different disperse phase volume fractions (phi = 0 to 0.394) and me an droplet radii (0.3 to 0.6 mu m) were measured at 25 degrees C. There wer e significant differences between the experimental measurements and theoret ical predictions due to droplet flocculation. The measured attenuation coef ficient was lower than expected at low frequencies because of thermal overl ap effects, but it was greater than expected at high frequencies because of scattering. These deviations could be accounted for using an effective med ium theory. Results suggest that ultrasonic velocities at 14 MHz were indep endent of droplet size and could be used to measure droplet concentration o f salad dressings.