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Control of ultrasonic waves in complex media : filtering, guiding and focusing
This manuscript is devoted to answer the following question: how can the complexity of a medium be exploited for controlling the propagation of acoustic waves?
The first part of the thesis is aimed at comparing the performances of a recent focusing technique (wave front shaping focusing) to these of time reversal focusing through multiple scattering media. It is highlighted that optimizing the amplitude and phase of acoustic waves using energy measurements at the focal point is sufficient to realize a spatial matched filter.
In a second part, the transverse localization regime is exploited to guide a wave while its temporal dispersion is mitigated. We show that an ultrasonic beam propagating along an array of scattering rods, the latter being randomly distributed in the transverse plane, remains confined into a cylinder whose diameter is smaller than of the sample.
The last part is devoted to the realization and the characterization
of controlled arrangements of air bubbles in fluid or solid matrix. It
is shown that the properties of these media can be explained by both
the concept of metamaterials and the concept of phononic crystals.
These new materials are designed to obtain band gaps due to both
bubbles resonances (“hybridization gap”) and ordered distribution
(“Bragg gap”).
Beyond possible applications such as acoustic filters,
these materials are of interest to clarify the role of resonance
hybridizations and lattice effects in the properties of locally
resonant crystals.