Electronique
Analyse par optimisation utilisant les algorithmes génétiques de filtres multi-cellulaires en guides d’ondes cylindriques métalliques creux
Dans ce travail, les dimensions géométriques de structures en guides d’ondes métalliquescreux, (transformateurs et filtres micro-onde à iris capacitifs, et à iris inductifs) sont calculéespar la méthode des circuits équivalents, ce-ci en partant d’un cahier de charge bienspécifique. La méthode de raccordement modal est utilisée pour l’analyse des résultatsobtenus. Vu que le cahier de charges n’était pas automatiquement réalisé, nous avons utiliséles algorithmes génétiques pour optimiser les résultats obtenus. Pour réduire le temps decalcul, nous avons essayé plusieurs fonctions d’évaluation, aussi, nous avons utilisé lesrésultats non optimisés, pour créer la population initiale d’individus. Pour la validation denotre travail, une bonne concordance est constatée entre nos résultats et ceux donnés pardeux logiciels de simulation. Voir les détails
Mots clés : optimization, Genetic algorithm, mode matching, filter, transformers.
Résolution de l’Equation d’Etat d’Ordre Fractionnaire
Fractional order systems are linear dynamical systems represented by linear fractional order differential equations given as: Da=Ax+Bu pour 0 < alpha < 1Therefore, the goal of this work is to present a resolution method of this type of fractional order state equation in order to facilitate its study, analysis and synthesis. The work realized and the results obtained for the resolution of this differential equation are based on Charef’s approximation method of irrational functions and the Cayley Hamilton’s technique for the resolution of regular linear differential equations. The impulse and the step responses of this type of systems have been derived. Illustrative exemples have been presented to test the resolution approach. A comparison with another method based on the so-called function of Mittag-Leffler has also been made to show the effectiveness of our resolution technique of the linear fractional order differential equation. Voir les détails
Mots clés : Fractional order systems, Cayley Hamilton’s technique, Functions of matrices, State space representation
Etude et simulation du comportement des matériaux diélectriques à fréquence fixe
L’objectif de ce mémoire est l’étude du comportement des matériaux diélectriquesainsi la simulation des lois de mélanges de ce comportement ; en employant la technique demesure SDT et à fréquence fixe pour le mélange qui est constitué par la résine époxyde etdeux titanates : BaTiO3 et CaTiO3 qui ont la structure PEROVSKITE.Plusieurs échantillons sont préparés, afin de voir l’évolution de la permittivité diélectrique de ce composite vis-à-vis les fractions volumiques des constituants qui s’étendentde zéro à trente pour cent.La simulation des lois de mélange de Lichtenecker et Bottreau nous a permis decomparer les résultats donnés par ces lois avec ceux obtenus expérimentalement qui montreque :· la loi de Bottreau est une généralisation de la loi de Lichtenecker.· La loi de Bottreau suit bien la réponse diélectrique pour ce type de mélange.La modélisation par réseau neurone nous a montré que la connaissance de la formedes agrégats dans le mélange est la base pour modéliser le comportement de ce type demélange Voir les détails
Mots clés : matériaux diélectriques, la TDR, permittivité diélectrique, la SDT
Fast Algorithm For Wavelet Thresholding In Presence Of Multiple Noisy Image Copies
This paper deals with the recovery of an image from noisy observations when multiple noisy copies of the image are available. Two configurations based on wavelet shrinkage algorithm and averaging technique are proposed. The performance of these methods is an improvement upon other methods proposed in the literature and are algorithmically simple for large computational saving. The proposed structures take a number of noisy copies of the image onto consideration in the computation of the threshold. Voir les détails
Mots clés : image denoising, Wavelets Thresholding, Multiresolution, Multiple Noisy Image copies
Comparaison de critères de détection efficace pour la sélection de l’ordre du modèle d’un signal InSAR à plusieurs composantes affecté par un bruit multiplicatif
Dans cet article, nous étudions le comportement des critères de détection efficace Efficient Detection Criteria (EDC) pour la détermination du nombre de composantes d’un signal InSAR affecté en plus d’un bruit additif par un bruit multiplicatif. Nous comparons les performances de ces critères tels que appliqués dans F. Gini et F. Bordoni (Mai 2003) (sans considérer le bruit multiplicatif) avec ceux appliqués en tenant compte, cette fois-ci, de la présence effective du bruit multiplicatif. Les résultats des simulations numériques montrent, qu’en général, l’approche proposée en tenant compte de la présence du bruit multiplicatif, présente de meilleures performances. Voir les détails
Mots clés : critères de théorie de l’information, bruit multiplicatif, layover, InSAR
Design and deformation behavior of high strength Fe–Mn–Al–Cr–C duplex steel
The influence of cold rolling reduction on microstructures and mechanical properties at room temperature of the duplex Fe–28Mn–7Al–5Cr–0.3C steel was investigated. In the Fe–28Mn–7Al alloy system, the duplex microstructure was obtained by lowering the carbon content to about 0.3 wt.%. The steel was austenito-ferritic with a low to moderate stacking fault energy. Two thermomechanical cycles were performed, which included cold rolling/annealing at 1100 °C, and cold rolling/annealing at 1100 °C/cold rolling/annealing at 1000 °C. The effects produced by cold rolling on the duplex steel were grain refinement and different strain-induced marks within the ferrite and austenite phases. They were easily observed within the austenite phase at a relatively smaller reduction than within the ferrite phase. Mechanical twinning plays a dominant role within the austenite phase during deformation at room temperature, resulting in extreme mechanical properties. No edge or longitudinal cracks were observed during cold rolling of the duplex steel. Voir les détails
Mots clés : Duplex steel, Cold rolling, Annealing, Microstructures, Austenite, Ferrite
The effect of a high temperature superconducting patch on a rectangular microstrip antenna
The complex resonant frequency problem of a superconductor patch is formulated in terms of an integral equation which is the kernel of a dyadic Green's function. To include the effect of the superconductivity of the microstrip patch, the surface complex impedance of the superconductor film is introduced using the two fluids model of Gorter and Casimir. The Galerkin procedure is used in the resolution of the electric field integral equation. Numerical results concerning the effect of the operating temperature of a superconductor patch on the characteristics of the antenna are presented. Voir les détails
Mots clés : Dyadic Green's function, Galerkin procedure, HTS microstrip patch, Microstrip antenna, Superconducting patch
Air gap tuning effect on the resonant frequency and half-power bandwidth of superconducting microstrip patch
An accurate analysis of an air gap tuned high Tc superconducting microstrip antenna is presented. To include the effect of the superconductivity of the microstrip patch in the Full wave analysis of the tunable rectangular microstrip patch, a surface complex impedance is considered. This impedance is determined by using London's equation and the model of Gorter and Casimir. Numerical results obtained are found to be in excellent agreement with the theoretical and experimental data available in the literature. Finally, numerical results for the air gap tuning effect on the operating frequency and bandwidth of the high Tc superconducting microstrip antenna are also presented. Voir les détails
Mots clés : Bandwidth, natural frequencies, Accurate analysis, Air gap tuning effect, Full wave analysis, Numerical results, Operating frequency, Rectangular microstrip patch, Superconducting microstrip antennas, Superconducting microstrips
Study of High Tc Superconducting Microstrip Antenna
Resonant characteristics of microstrip antennas with superconducting films is presented. The analysis is based on a full electromagnetic wave model with London's equations and the two-fluid model. It is shown that the full-wave analysis presented here gives numerical results which are in excellent agreement with the measured data available in the literature. Re- sults showing the effect of the temperature on the resonant frequency and half-power bandwidth of superconducting microstrip antenna are given. Variations of the resonant frequency with the high Tc superconducting film thickness are also presented. Voir les détails
Mots clés : Electromagnetic waves, microstrip antennas, Superconducting films, Full wave analysis, High-T, Numerical results, Resonant characteristics, Superconducting microstrip antennas, Two fluid model
Bayesian Pressure Snake forWeld Defect Detection
Image Segmentation plays a key role in automatic weld defect detectionand classification in radiographic testing. Among the segmentation methods,boundary extraction based on deformable models is a powerful techniqueto describe the shape and then deduce after the analysis stage, the type of thedefect under investigation. This paper describes a method for automatic estimationof the contours of weld defect in radiographic images. The method uses astatistical formulation of contour estimation by exploiting statistical pressuresnake based on non-parametric modeling of the image. Here the edge energy isreplaced by a region energy which is a function of statistical characteristics ofarea of interest. Voir les détails
Mots clés : Snake, images segmentation, pdf estimation, radiographic images, Non Destructive Inspection