Déconvolution adaptative pour le contrôle non destructif par ultrasons

This thesis deals with the ultrasonic non destructive testing of industrial parts. During real experiments, the signals received by the acoustic transducer are analyzed to detect the discontinuities of the part under test. This analysis can be a difficult task due to digital acquisition, propagation effects and echo overlapping if discontinuities are close. Sparse deconvolution is an inverse method that aims to estimate the precise positions of the discontinuities. The underlying hypothesis of this method is a sparse distribution of the solution, which means there are a few number of discontinuities. In the literature, deconvolution is addressed by a linear time-invariant model as a function of propagation distance, which in reality does not hold.The purpose of this thesis is therefore to develop a model and associated methods in order to cancel the effects of acquisition, propagation and echo overlapping. The first part is focused on the direct model development. In particular, we build a linear time-variant model that takes into account dispersive attenuation. This model is validated with experimental data acquired from attenuative materials. The second part of this work concerns the development of efficient sparse deconvolution algorithms, addressing the minimization of a least squares criterion penalized by a L0 pseudo-norm. Specific algorithms are developed for up-sampled deconvolution, and more robust exploration strategies are built for data containing oscillating waveforms. By using synthetic and experimental data, we show that the developed methods lead to better results compared to standard approaches for a competitive computation time. The proposed methods are then applied to real non destructive testing problems where they confirm their efficiency.Nous nous intéressons au contrôle non destructif par ultrasons des matériaux industriels. En pratique, les signaux réceptionnés par le transducteur ultrasonore sont analysés pour détecter les discontinuités de la pièce inspectée. L'analyse est néanmoins rendue difficile par l'acquisition numérique, les effets de la propagation ultrasonore et la superposition des échos lorsque les discontinuités sont proches. La déconvolution parcimonieuse est une méthode inverse qui permet d'aborder ce problème afin de localiser précisément les discontinuités. Ce procédé favorise les signaux parcimonieux, c'est à dire ne contenant qu'un faible nombre de discontinuités. Dans la littérature, la déconvolution est généralement abordée sous l'hypothèse d'un modèle invariant en fonction de la distance de propagation, modalité qui n'est pas appropriée ici car l'onde se déforme au cours de son parcours et en fonction des discontinuités rencontrées. Cette thèse développe un modèle et des méthodes associées qui visent à annuler les dégradations dues à l'instrumentation et à la propagation ultrasonore, tout en résolvant des problèmes de superposition d'échos. Le premier axe consiste à modéliser la formation du signal ultrasonore en y intégrant les phénomènes propres aux ultrasons. Cette partie permet de construire un modèle linéaire mais non invariant, prenant en compte l'atténuation et la dispersion. L'étape de modélisation est validée par des acquisitions avec des matériaux atténuants. La deuxième partie de cette thèse concerne le développement de méthodes de déconvolution efficaces pour ce problème, reposant sur la minimisation d'un critère des moindres carrés pénalisé par la pseudo-norme L0. Nous avons développé des algorithmes d'optimisation spécifiques, prenant en compte, d'une part, un modèle de trains d'impulsions sur-échantillonné par rapport aux données, et d'autre part le caractère oscillant des formes d'onde ultrasonores. En utilisant des données synthétiques et expérimentales, ces algorithmes associés à un modèle direct adapté aboutissent à de meilleurs résultats comparés aux approches classiques pour un coût de calcul maîtrisé. Ces algorithmes sont finalement appliqués à des cas concrets de contrôle non destructif où ils démontrent leur efficacité

Inspection of Steel Welds Using Total Focusing Method Imaging

The ultrasonic control of steel welds is crucial in the oil and gas transportation industry. The state-of-the-art method is zonal focusing which consists in focusing the ultrasonic beam at specific distances using a wedge in order to check the integrity of specific zones in the weld. Advanced methods such as the total focusing method (TFM) give potentially better images in terms of signal to noise ratio and flaw resolution [1]. Moreover, a complete view of the weld is possible using TFM, contrary to zonal focusing. In this paper, we present a fast implementation of the TFM imaging for weld inspection using wedges. In particular, we propose a GPU implementation that tremendously accelerates the process and makes nearly real-time applications possible. The configuration with two media necessitates an optimization iterative procedure to estimate the proper times of flight, which is implemented in the GPU as well. We also present several skip modes in order to visualize different flaw orientations and locations in the weld (cap, root, etc.). First, we give imaging results on an aluminum block containing artificial flaws such as porosity or lack of fusion. We make a comparison between TFM and conventional imaging, and show that TFM gives better results in terms of image quality (SNR, resolution). Finally, we show results of a real girth weld inspection and demonstrate that the use of TFM is definitely interesting in this context

Blind Sparse Deconvolution of Regularly Spaced Ultrasonic Echoes for Thickness Measurement

We present a method for estimating the thickness of thin materials from ultrasonic data, in the context of coating measurement or thickness estimation of tubes and pipes. When sending an ultrasonic pulse in normal incidence in a homogeneous material, a set of regularly spaced echoes is received. Thickness is then obtained from the estimation of the time delay between echoes. If thin structures are inspected (or if a low frequency transducer is used), then echoes may overlap. Then, visual interpretation is made difficult and standard automatic methods may fail. We propose a blind sparse deconvolution approach to this problem, where data are modeled as the convolution of a spike train with an unknown impulse response that corresponds to the shape of the echoes. The specific structure of the spike train (regularly spaced spikes with geometrically decreasing amplitudes) is taken into account and the echoes are modeled with a frequency modulated Gaussian signal. Joint estimation of all parameters is performed by non-linear least-squares minimization, with specific constraints, initialization and optimization procedure that aim to avoid local minima. Results are presented on simulated data and in application to thickness estimation of aluminum plates with 2mm and 1mm thickness

Multidimensional Measures of Physical Activity and Their Association with Gross Motor Capacity in Children and Adolescents with Cerebral Palsy.

The current lack of adapted performance metrics leads clinicians to focus on what children with cerebral palsy (CP) do in a clinical setting, despite the ongoing debate on whether capacity (what they do at best) adequately reflects performance (what they do in daily life). Our aim was to measure these children's habitual physical activity (PA) and gross motor capacity and investigate their relationship. Using five synchronized inertial measurement units (IMU) and algorithms adapted to this population, we computed 22 PA states integrating the type (e.g., sitting, walking, etc.), duration, and intensity of PA. Their temporal sequence was visualized with a PA barcode from which information about pattern complexity and the time spent in each of the six simplified PA states (PAS; considering PA type and duration, but not intensity) was extracted and compared to capacity. Results of 25 children with CP showed no strong association between motor capacity and performance, but a certain level of motor capacity seems to be a prerequisite for the achievement of higher PAS. Our multidimensional performance measurement provides a new method of PA assessment in this population, with an easy-to-understand visual output (barcode) and objective data for clinical and scientific use

Walking Speed of Children and Adolescents With Cerebral Palsy: Laboratory Versus Daily Life.

The purpose of this pilot study was to compare walking speed, an important component of gait, in the laboratory and daily life, in young individuals with cerebral palsy (CP) and with typical development (TD), and to quantify to what extent gait observed in clinical settings compares to gait in real life. Fifteen children, adolescents and young adults with CP (6 GMFCS I, 2 GMFCS II, and 7 GMFCS III) and 14 with TD were included. They wore 4 synchronized inertial sensors on their shanks and thighs while walking at their spontaneous self-selected speed in the laboratory, and then during 2 week-days and 1 weekend day in their daily environment. Walking speed was computed from shank angular velocity signals using a validated algorithm. The median of the speed distributions in the laboratory and daily life were compared at the group and individual levels using Wilcoxon tests and Spearman's correlation coefficients. The corresponding percentile of daily life speed equivalent to the speed in the laboratory was computed and observed at the group level. Daily-life walking speed was significantly lower compared to the laboratory for the CP group (0.91 [0.58-1.23] m/s vs 1.07 [0.73-1.28] m/s, p = 0.015), but not for TD (1.29 [1.24-1.40] m/s vs 1.29 [1.20-1.40] m/s, p = 0.715). Median speeds correlated highly in CP (p < 0.001, rho = 0.89), but not in TD. In children with CP, 60% of the daily life walking activity was at a slower speed than in-laboratory (corresponding percentile = 60). On the contrary, almost 60% of the daily life activity of TD was at a faster speed than in-laboratory (corresponding percentile = 42.5). Nevertheless, highly heterogeneous behaviors were observed within both populations and within subgroups of GMFCS level. At the group level, children with CP tend to under-perform during natural walking as compared to walking in a clinical environment. The heterogeneous behaviors at the individual level indicate that real-life gait performance cannot be directly inferred from in-laboratory capacity. This emphasizes the importance of completing clinical gait analysis with data from daily life, to better understand the overall function of children with CP

Can the evaluation of marker placement confidence be used as an indicator of gait kinematic variability?

IntroductionThree-dimensional gait analysis is widely used for the clinical assessment of movement disorders. However, measurement error reduces the reliability of kinematic data and consequently assessment of gait deviations. The identification of high variability is associated with low reliability and those parameters should be ignored or excluded from gait data interpretation. Moreover, marker placement error has been demonstrated to be the biggest source of variability in gait analysis and may be affected by factors intrinsic to the evaluators such as the evaluator's expertise which could be appraised through his/her experience and confidence in marker placement.ObjectivesIn the present study, we hypothesized that confidence in marker placement is correlated with kinematic variability and could potentially be used as part of a score of reliability. Therefore, we have proposed a questionnaire to evaluate qualitatively the confidence of evaluators in lower-limb marker placement. The primary aim of this study was to evaluate the reliability and validity of the presented questionnaire. The secondary objective was to test a possible relationship between marker placement confidence and kinematics variability.MethodsTo do so, test-retest gait data were acquired from two different experimental protocols. One protocol included data from a cohort of 32 pathological and 24 asymptomatic subjects where gait analysis was repeated three times, involving two evaluators. A second protocol included data from a cohort of 8 asymptomatic adults with gait analysis repeated 12 times, per participant, and involving four evaluators with a wider range of experience.ResultsResults demonstrated that the questionnaire proposed is valid and reliable to evaluate qualitatively the confidence of evaluators in placing markers. Indeed, confidence scores were correlated with the actual variability of marker placement and revealed the evaluator's experience and the subjects' characteristics. However, no correlation was observed between confidence scores and kinematic variability and the formulated hypothesis was not supported

Adaptative deconvolution for ultrasonic non destructive testing

Nous nous intéressons au contrôle non destructif par ultrasons des matériaux industriels. En pratique, les signaux réceptionnés par le transducteur ultrasonore sont analysés pour détecter les discontinuités de la pièce inspectée. L'analyse est néanmoins rendue difficile par l'acquisition numérique, les effets de la propagation ultrasonore et la superposition des échos lorsque les discontinuités sont proches. La déconvolution parcimonieuse est une méthode inverse qui permet d'aborder ce problème afin de localiser précisément les discontinuités. Ce procédé favorise les signaux parcimonieux, c'est à dire ne contenant qu'un faible nombre de discontinuités. Dans la littérature, la déconvolution est généralement abordée sous l'hypothèse d'un modèle invariant en fonction de la distance de propagation, modalité qui n'est pas appropriée ici car l'onde se déforme au cours de son parcours et en fonction des discontinuités rencontrées. Cette thèse développe un modèle et des méthodes associées qui visent à annuler les dégradations dues à l'instrumentation et à la propagation ultrasonore, tout en résolvant des problèmes de superposition d'échos. Le premier axe consiste à modéliser la formation du signal ultrasonore en y intégrant les phénomènes propres aux ultrasons. Cette partie permet de construire un modèle linéaire mais non invariant, prenant en compte l'atténuation et la dispersion. L'étape de modélisation est validée par des acquisitions avec des matériaux atténuants. La deuxième partie de cette thèse concerne le développement de méthodes de déconvolution efficaces pour ce problème, reposant sur la minimisation d'un critère des moindres carrés pénalisé par la pseudo-norme L0. Nous avons développé des algorithmes d'optimisation spécifiques, prenant en compte, d'une part, un modèle de trains d'impulsions sur-échantillonné par rapport aux données, et d'autre part le caractère oscillant des formes d'onde ultrasonores. En utilisant des données synthétiques et expérimentales, ces algorithmes associés à un modèle direct adapté aboutissent à de meilleurs résultats comparés aux approches classiques pour un coût de calcul maîtrisé. Ces algorithmes sont finalement appliqués à des cas concrets de contrôle non destructif où ils démontrent leur efficacité.This thesis deals with the ultrasonic non destructive testing of industrial parts. During real experiments, the signals received by the acoustic transducer are analyzed to detect the discontinuities of the part under test. This analysis can be a difficult task due to digital acquisition, propagation effects and echo overlapping if discontinuities are close. Sparse deconvolution is an inverse method that aims to estimate the precise positions of the discontinuities. The underlying hypothesis of this method is a sparse distribution of the solution, which means there are a few number of discontinuities. In the literature, deconvolution is addressed by a linear time-invariant model as a function of propagation distance, which in reality does not hold.The purpose of this thesis is therefore to develop a model and associated methods in order to cancel the effects of acquisition, propagation and echo overlapping. The first part is focused on the direct model development. In particular, we build a linear time-variant model that takes into account dispersive attenuation. This model is validated with experimental data acquired from attenuative materials. The second part of this work concerns the development of efficient sparse deconvolution algorithms, addressing the minimization of a least squares criterion penalized by a L0 pseudo-norm. Specific algorithms are developed for up-sampled deconvolution, and more robust exploration strategies are built for data containing oscillating waveforms. By using synthetic and experimental data, we show that the developed methods lead to better results compared to standard approaches for a competitive computation time. The proposed methods are then applied to real non destructive testing problems where they confirm their efficiency

Chalcogenide glass optical fibers for the mid-infrared : towards new sources and solutions for infrared spectroscopy

Les travaux de cette thèse étaient consacrés à l’élaboration de fibres optiques en verres de chalcogénures présentant un intérêt pour le domaine de la spectroscopie infrarouge. Dans un premier temps, des fibres à saut d’indice composées de verre ([GeS2]0,80 [Ga2S3]0,20)0,90 (CsCl)0,10 pour la gaine et de verre ([GeS2]0,80 [Ga2S3]0,20)0,90 (CdI2)0,10 pour le cœur ont été développées dans le but de réaliser à plus long terme un laser à fibre pour des longueurs d’onde du moyen infrarouge (entre 3 et 8 µm). Le choix de ces verres s’est appuyé sur une étude des propriétés thermiques, puis une étude de leurs propriétés optiques (linéaires et non linéaires). Les préformes destinées à être fibrées ont ensuite été élaborées par la méthode du rod-in-tube. De plus, ces verres présentent la particularité d’être photosensible ce qui permettrait la photoinscription par un laser femtoseconde de miroirs de Bragg nécessaire à l’obtention d’une cavité laser. Le verre de cœur a ensuite pu être dopé par des ions Pr3+ et une émission dans une fibre cœur/gaine a pu être observée permettant d’envisager positivement l’émission au sein d’une future cavité laser. Dans un second temps, les travaux de cette thèse se sont focalisés sur la réalisation de fibres optiques microstructurées à cœur creux. La réalisation de ce type de fibre, notamment à base de verres de chalcogénures tel que le verre de composition Te20As30Se50, pourrait permettre d’atteindre de très faibles pertes optiques jusqu’à la longueur d’onde de 20 µm, ainsi que le transport de faisceau de laser de puissance. Pour produire les préformes à cœur creux destinées à être fibrées, deux méthodes ont été utilisées : la méthode classique du stack and draw et la méthode originale de l’impression 3D de verres de chalcogénures. Cette dernière méthode a d’ailleurs été développée au cours de cette thèse et a montré son fort potentiel pour l’élaboration d’objets imprimés qui pourraient prétendre à des applications optiques comme des capteurs infrarouges par exemple.This PhD work was devoted to the development of chalcogenide glass optical fibers for infrared spectroscopy. First, step index fibers composed of a cladding glass ([GeS2]0.80 [Ga2S3]0.20)0.90 (CsCl)0.10 and a core glass ([GeS2]0.80 [Ga2S3]0.20)0.90 (CdI2)0.10 have been developed. The choice of the two glasses has been down through the measurements of their thermal and optical properties among numerous other glass compositions. The development of such optical fibers in this photosensitive glass system was strongly motivated by the future realisation of a fibre laser emitting in the 3-5 µm mid infrared region. In addition, they would allow the femtosecond laser inscription of Bragg mirrors, which are necessary to obtain a laser cavity. In this context, the core glass has been doped with Pr3+ ions and spontaneous emission has been observed around 4 µm in a step- index fiber. Secondly, this work was focused on the elaboration of hollow core microstructured optical fibers made with chalcogenide glasses. With this type of structure, it is possible to consider transmission fiber up to 20 µm while having a very low attenuation eventually below 50 dB/km. In addition, holding the power flow of such fibers would be greatly improved compared to that of the solid core fibers . To produce hollow core preforms, two methods were used: the classic stack and draw method and an innovative method adapted to chalcogenide glass 3D printing. The 3D printing method was particularly developed during this thesis and has shown its strong potential for the development of printed objects that could result in many optical applications such as infrared sensors for example