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Contribution expérimentale à l'étude de la diffusion multiple des ultrasons en régimes de propagation linéaire et non linéaire

Abstract : This experimental thesis work focuses on the linear and nonlinear propagation of ultrasounds in highly heterogeneous random media. In the nonlinear regime, we investigate the coherent transmission of a shock wave through two models of heterogeneous random media: a forest of metal rods immersed in water, and a bubbly gel. The experiment shows that the effects of the nonlinearity and of the multiple scattering are decoupled. We then take advantage of the large spectrum of the incident shock wave to measure the attenuation and the group velocity of the coherent wave in the medium, on a very large frequency band. By comparing our measurements to a linear theory including second order spatial correlations between scatterers, we extend its range of validity, and we show that a shock wave is a promising tool for spectroscopy of highly heterogeneous medium. Using the same experimental setup, we report the first measurement of an ultrasonic coda transmitted by a bubbly medium. In the linear propagation regime, we use the coda generated by the multiple scattering to measure the transport parameters in the forests of metal rods immersed. We present both broadband and frequency-resolved measurements of the diffusion constant of ultrasounds in these media. These latters show the interest to study the coda, which provides better frequency-resolved measurements than the coherent wave. Finally, we present the first frequency-resolved measurements of the velocity of transport for these model media. With these measurements, we now have a fully characterized synthetic heterogeneous medium.
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Contributor : Nicolas Viard Connect in order to contact the contributor
Submitted on : Wednesday, March 5, 2014 - 4:21:19 PM
Last modification on : Sunday, June 26, 2022 - 2:18:41 AM
Long-term archiving on: : Thursday, June 5, 2014 - 11:45:30 AM


  • HAL Id : pastel-00955942, version 1


Nicolas Viard. Contribution expérimentale à l'étude de la diffusion multiple des ultrasons en régimes de propagation linéaire et non linéaire. Acoustique [physics.class-ph]. Université Paris-Diderot - Paris VII, 2014. Français. ⟨pastel-00955942⟩



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