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Theses

Imagerie et caractérisation instationnaire de sources acoustiques en milieu réverbérant et bruité par renversement temporel et séparation de champs sur antenne hémisphérique double couche

Abstract : For many industrial applications, it is necessary to inspect radiating structures using non-stationary sources localization and characterization techniques. In the last decades, many acoustical imaging methods have been developed. These techniques are based on the measurement of a set of acoustical quantities (pressure and/or particle velocity) on structured (or not) microphones antennas. In particular, this thesis work aims at studying and optimizing non-stationary imaging methods using time reversal. More particularly, we are interested in improvements following to assess precisely the acoustic field with good performances, by making these methods performances insensitive to the measurements conditions (reverberant and noisy environment). For purpose, several improvements are proposed in this manuscript, thanks to measurements realised on a hemispherical double layer antenna. In particular, we detail a quantitative time reversal acoustical imaging process thanks to the calculation of the time reversed version of the Helmholtz-Kirchhoff integral, using the "double data" measurements realised on the antenna. Then, we will detail improvements to suppress both room effects and the perturbative sources contributions thanks to a field separation method, which consists in expanding the measured data onto spherical harmonics functions basis. Then, the "incoming" and the "outgoing" contributions are separated. Finally, the time reversal imaging resolution, intrinsically limited, is improved thanks to the automatic definition of a time reversal sink. Its analytical formulation takes advantage of double layer measurement structure. This of crucial importance to note that all these improvements take advantage from the recording of a double data set (pressure-pressure or pressure-velocity). The quality of the pressure field reconstructed using the full double layer time reversal imaging process is illustrated through numerical and experimental studies, from an idealized situation (anechoic and not noisy environments) to a hard case (highly reverberant and noisy environment).
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https://tel.archives-ouvertes.fr/tel-01359612
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Submitted on : Friday, September 2, 2016 - 5:31:08 PM
Last modification on : Monday, February 21, 2022 - 3:38:07 PM
Long-term archiving on: : Sunday, December 4, 2016 - 8:46:47 AM

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Stéphanie Lobréau. Imagerie et caractérisation instationnaire de sources acoustiques en milieu réverbérant et bruité par renversement temporel et séparation de champs sur antenne hémisphérique double couche. Acoustique [physics.class-ph]. Conservatoire national des arts et metiers - CNAM, 2015. Français. ⟨NNT : 2015CNAM0993⟩. ⟨tel-01359612⟩

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