Stochastic methods for the analysis of couplings in Electromagnetic Compatibility and contribution to the reliability of electronic systems
Application de méthodes probabilistes à l'analyse des couplages en Compatibilité électromagnétique et contribution à la sûreté de fonctionnement de systèmes électroniques
Résumé
Increasing use of electronic devices and multiplicity of sources of disturbance led to the study of new test facilities making it possible to improve the repetivity of measurements of Electromagnetic Compatibility (EMC), in particular at frequencies higher than the Gigahertz. In this context, the Reverberation Chamber (RC) represents an attractive tool, as well in immunity measurements as in emission. However, many questions remain still open for the behaviour of the RC, in presence or not of the equipment under test : the purpose of the work presented in this thesis is to contribute a share to the probabilistic shutter of the study of the electromagnetic field in RC. Starting from statistical tests and experimental measurements, the legitimacy in real RC is verified with the various assumptions relating to the electromagnetic fields generated in "ideal" reverberating environment. Under this condition, the study of a line of transmission showed the influence of directivity in the relation between the electric fields of calibration in Anechoic Chamber (AC) and RC, for an identical value of the current induced at its termination. In addition, it is important to apprehend in which direction the environment in RC can "be compared" with that generated inside half-closed enclosures (vehicle) subjected to an external disturbing electromagnetic field. In order to bring first steps of answers to this question, it is presented a comparison of the statistical parameters of the electromagnetic field, characterizing these two types of environments. Lastly, the assumptions checked in high frequency ("ideal" environment reverberating, losses of the prevalent walls), led to the development of an original probabilistic model consisting of assimilating the RC to a cavity whose walls are characterized by a random conductivity. The probabilistic density function of this random variable is established starting from formulation and measurement results validated in the high frequencies. This model of conductivity is then proposed for the resolution of the Maxwell's equations by a stochastic collocation method. It is shown that a low number of simulations of the cavity without stirrer can replace the deterministic modelling of the RC as a whole, for the estimation of the statistical parameters of the electric field generated in the working volume of the structure. In addition, the application of the stochastic collocation method to the formalism previously validated for the study of wires immersed in a cavity led to an effective and realistic modelling of a radiated wire in RC.
L'utilisation croissante d'appareils électroniques et la multiplicité des sources de perturbation ont conduit à l'étude de nouveaux moyens d'essais permettant d'améliorer la répétitivité des mesures en Compatibilité ElectroMagnétique (CEM), en particulier aux fréquences supérieures au GigaHertz. Dans ce contexte, la Chambre Réverbérente à Brassage de Modes (CRBM) représente un outil attractif, tant au niveau des mesures en immunité qu'en émission. Cependant, de nombreuses questions restent encore ouvertes quand au comportement des CRBM, en présence ou non de l'équipement sous test : les travaux représentés dans ce mémoire ont pour but d'apporter une contribution au volet probabiliste de l'étude du champ électromagnétique en CRBM
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