Application du retournement temporel en micro-ondes à l'amplification d'impulsions et l'imagerie

Abstract : Time Reversal (TR) methods are applied in microwaves to pulse amplification and imaging. First, we use a reverberation chamber with an aperture on the front face and we take advantage of the pulse compression property of time reversal. High amplitude peaks are generated outside the chamber thanks to the long spreading time of the signals inside. Our device is auto-adaptive in position and in polarization. The second part of the manuscript deals theoretically and experimentally with the DORT method (decomposition of the TR operator). The method is first applied to characterize a dielectric cylinder and work out its parameters. Imaging of two close scatterers separated by a subwavelength distance is then considered. A criterion is especially extracted to deduce the noise level above which the resolution fails. Furthermore, we use the DORT method to track experimentally people behind a wall. The wave propagation inside the wall is taken into account to localize a human being. This last part leads to the study of the invariants of the TR operator when a pointlike target is moving during the acquisition of the transfer matrix. Eventually, we introduce the first wideband ambient noise cross-correlation experiment in microwaves. The crosscorrelation yields the Green's function between two antennas and allows the passive detection and localization of targets. The analogy with a TR process is developed. Passive people localization is also achieved with the narrow bandwidth signals emitted by a WIFI router.
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Submitted on : Monday, December 6, 2010 - 10:40:29 AM
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Matthieu Davy. Application du retournement temporel en micro-ondes à l'amplification d'impulsions et l'imagerie. Optique [physics.optics]. Université Paris-Diderot - Paris VII, 2010. Français. ⟨pastel-00543221⟩

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