Diffusion multiple et renversement du temps ultrasonore dans des milieux périodiques et désordonnés

Abstract : In this thesis, we have experimentally studied several aspects of acoustic wave propagation through ordered and disordered heterogeneous media.

First of all, we have built and characterized periodic samples, that are called "phononic crystals". These materials behave as efficient frequency filters, and present great technological and theoretical interest. We have studied the group time through monocrystals, which revealed an effect analogous to the tunneling effect classically encountered in quantum mechanics. Through a Fabry-Perot structure made up of two phononic crystals, we have identified resonances in the transmission spectrum. At these frequencies, the group time shows that waves are trapped inside the cavity, as in quantum resonant tunneling. These results are supported by numerical simulations.
Time reversal experiments through phononic crystals have revealed an absence of hyperfocusing, which is a characteristic of disordered samples.

With bubble clouds, we have tried to bring to light the nonlinear multiple scattering regime.
To that end, we have built an experimental setup which enabled us to generate quite reproducible bubble clouds. Several methods were used to obtain the bubble radius distribution function, one of which allowed us to estimate the void fraction.
Low bubble densities did not allow the observation of a strong multiple scattering regime, and the origin of the measured non-linearities remains unsure.
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https://tel.archives-ouvertes.fr/tel-00011354
Contributor : François van der Biest <>
Submitted on : Tuesday, January 17, 2006 - 6:49:46 PM
Last modification on : Thursday, July 4, 2019 - 11:00:03 AM
Long-term archiving on : Monday, September 20, 2010 - 2:05:02 PM

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  • HAL Id : tel-00011354, version 2

Citation

François van der Biest. Diffusion multiple et renversement du temps ultrasonore dans des milieux périodiques et désordonnés. Acoustique [physics.class-ph]. Université Paris-Diderot - Paris VII, 2005. Français. ⟨tel-00011354v2⟩

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