Abstract
We report on frequency-resolved experimental measurements of the ultrasonic diffusivity in the MHz range. By means of robotics, we produced a highly monodisperse suspension made of soft metallic micro-beads randomly-dispersed in a water-based gel-matrix. The measured diffusion coefficient is shown to vary significantly with frequency by more than one order of magnitude that is probably due to the sharp scattering resonances of the metallic particles.
Highlights
Classical waves, such as light or sound, propagating in a random medium progressively lose their coherence and behave diffusively, to classical particles [1]
We report on frequency-resolved experimental measurements of the ultrasonic diffusivity in the MHz range
Viard and Derode measured the ultrasonic diffusivity that was shown to vary with frequency, sometimes by more than a factor 2, in these systems composed of rigid metallic scatterers [10]
Summary
Classical waves, such as light or sound, propagating in a random medium progressively lose their coherence and behave diffusively, to classical particles [1]. Tallon et al found interestingly that the energy velocity that describes the transport of energy by the dominant diffusive waves is mainly governed by the sound speed within the scatterers, and can be either much slower or faster than any of the other wave velocities by investigating highly monodisperse resonant emulsions containing either "slow" oil droplets (sound speed c1 less than c0 of the surrounding fluid) or "fast" liquid metallic droplets (c1 > c0) [13].
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