Phase velocity of ultrasound in suspensions of large particles

The phase velocity of ultrasound was measured in suspensions of spherical g lass particles in water with particle size parameters (particle size / wave length) ranging from ca. 0.01 to 40. Two different measurement techniques h ave been tested: i) A narrow-band tone-burst (tb) setup with comparison of the signals that have run through the suspension with the pure fluid signal s, and ii) a continuous-wave (cw) technique that evaluates the phase-shift between the transmitted and the received wave. In both cases, phase velocit y could be measured with attenuations of up to 80 dB, allowing for particle concentrations of up to 30% by volume. As far as the authors know, measure ments in this combination of wavelength and concentration have never been p ublished before. Although the two methods bear out quite different results, none of them has to be wrong; the stationary phase velocity, measurable wi th the cw-technique, might differ from the transient phase velocity. The ex perimental results are compared with two theoretical models, one for the ra nge of intermediate particle size parameters, where viscous drag and pressu re gradient forces are the dominant particle-wave interaction mechanisms, a nd one for the scattering dominated regime of wavelength less than or equal to particle Sizes. The best fit is obtained with the tone-burst technique and a newly developed model based on the dispersion equation.