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Theses

Méthodes d'imagerie ultrasonore avancées et rapides pour le contrôle non destructif de matériaux atténuants et diffusants

Abstract : The development of multi-element probes and continuous progress in electronics have favored the generalization of ultrasonic imaging methods for non destructive testing (NDT). In particular, the total focusing method is widely used due to its simplicity and real-time capability. Nevertheless, the resolution and contrast of the resulting images are limited due to the oscillating nature of the ultrasonic wave. This work addresses ultrasonic imaging from an inverse problem perspective. Retrieving the reflectivity map from ultrasonic measurements acquired with band-limited transducers is an ill-posedproblem. In this work, we develop inversion methods based on a regularization framework that enhances both the sparsity and the spatial smoothness of the reconstructed solution. Therefore, we assume that the reflectivity map is mainly homogeneous and possibly contains only few reflectors of small size. A first contribution describes the implementation and the inversion of a linear model that relates the raw, large-size, ultrasonic data to the reflectivity image, through a matrix containing the ultrasonic waveforms. A second contribution consists in projecting the previous model involving raw ultrasonic data in the space domain through a linear beamforming method. The size of the resulting model is therefore reduced, and its inversion can be interpreted as a deconvolution problem with a non stationary point spread function and colored noise. We hence propose an interpolation model in order to obtain a computationally efficient method. Finally, the last part of this work consists in applying the proposed methods to media with complex acoustic properties, such as frequency attenuation and dispersion, where the ultrasonic waveform is distorted during propagation. These algorithms are applied to synthetic data and practical NDT cases and show superior resolving capabilities compared to standard methods, at the cost of higher computational complexity.
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https://tel.archives-ouvertes.fr/tel-03651196
Contributor : Abes Star :  Contact
Submitted on : Monday, April 25, 2022 - 3:28:14 PM
Last modification on : Thursday, May 5, 2022 - 3:31:28 AM

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  • HAL Id : tel-03651196, version 1

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Nans Laroche. Méthodes d'imagerie ultrasonore avancées et rapides pour le contrôle non destructif de matériaux atténuants et diffusants. Traitement du signal et de l'image [eess.SP]. École centrale de Nantes, 2021. Français. ⟨NNT : 2021ECDN0036⟩. ⟨tel-03651196⟩

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