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"Come and see how oil droplets slow down the propagation of sound waves”, Benoit Tallon
Start Date: 10/12/2018Start Time: 3:30 PM
End Date: 10/12/2018End Time: 5:00 PM
Event Description:

"Come and see how oil droplets slow down the propagation of sound waves”

Confer with Benoit Tallon in the coffee room Friday October 12, 2018. 

-- 3:30 pm -  Caffeine, confections and congeniality.

-- 5:15 pm -  Quaff, peck and ponder.

Hosted by the P&A graduate students. 

Lecture commences at 4:00 pm in 330 Allen Building.

Benoit Tallon

University of Manitoba. 

Title: “Resonant multiple scattering of ultrasound in disordered media” 

Abstract:

Ultrasonic pulse propagation experiments are reported on dilute suspensions of fluorinated-oil droplets immersed in a water-based gel matrix. These resonant emulsions are model systems for studying the effects of scattering resonances on wave transport since the large sound-speed contrast between the scatterers and the surrounding medium enhances the shape resonances of the liquid particles. Measurements of the ballistic component reveal that both the scattering mean free path and the group velocity strongly depend on the frequency as predicted by a simple model based on the Independent Scattering Approximation. Scattering resonances are also responsible for very slow diffusivity of the multiply scattered ultrasound. This slowing down of the diffusion process due to resonances is well captured by models that include additional scattering delays of the ultrasonic pulses. The relationship between the diffusion coefficient and the ballistic data allow the frequency dependence of energy velocity of diffusing waves to be estimated, and show that the energy and group velocities are very different in our system. Although our ultrasonic measurements and their interpretation give a complete picture of wave transport in dilute resonant emulsions, the description of the wave transport in concentrated emulsions requires more sophisticated models based on the spectral function approach and the self-consistent theory.

Benoitt tallon

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