COMPARISON OF MULTIPLE-SCATTERING THEORIES WITH EXPERIMENTAL MEASUREMENTS IN EMULSIONS

The ultrasonic velocity and attenuation coefficient of a series of n-hexadecane-in-water emulsions have been measured as a function of disperse phase volume fraction (phi = 0 to 0.56), particle size (r32 = 0.1 to 1.8-mu-m), and frequency (f = 0.2 to 7 MHz). These measurements are compared with predictions of the velocity and attenuation made using the multiple scattering theories of Waterman and Truell [J. Math. Phys. 2, 512-537 (1962)], Lloyd and Berry [Proc. Phys. Soc. London 91, 678-688 (1967)], and Ma et al. [J. Acoust. Soc. Am. 87, 2779-2782 (1990)] in the long wavelength limit. All the theories give good agreement with the experimental measurements for dilute emulsions (phi < 0.13). In the more concentrated emulsions the theories agree less well, especially at low frequencies and particle sizes. Possible reasons for the discrepancies between the theories and experimental results are discussed.