Diffusing Acoustic Wave Transport and Spectroscopy
Measurements of the diffusive transport of ultrasonic waves have been performed to critically test the applicability of the diffusion approximation for multiply scattered sound. By performing these measurements over an extended range of frequencies, we have shown that the energy velocity of diffusing ultrasound is similar in magnitude and frequency dependence to the group velocity, giving a unified physical picture of the velocities of energy transport by both diffusive and ballistic wave pulses. This information on diffusive transport of ultrasound has facilitated the development of a new ultrasonic technique, Diffusing Acoustic Wave Spectroscopy (DAWS), for probing the dynamics of structured media. The feasibility and sensitivity of DAWS has been demonstrated by studying the motion of particles in fluidised suspensions, providing important new information on the velocity fluctuations and local strain rate of fluidised particles.
KeywordsUltrasonic Wave Diffusive Transport Glass Sphere Field Fluctuation Ultrasonic Technique
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