Field Statistics in a One-Dimensional Reverberation Chamber Model

This work focuses on building a fairly simple yet physically appropriate 1D model for a Reverberation Chamber which claims to be able to analytically predict the statistical behavior of such a chamber, without forsaking to the benefits of deterministic models. The statistical properties are introduced by varying the size of a 1D stirrer or the cavity size itself. A validation analysis shows agreement with other theories and measured results on real RCs. Field statistics in undermoded regime is examined. A radiated emission test is defined and shows reliable matching with reality. The field performance near the conducting walls is investigate

Psychomotricité et émergence de la représentation

Cet article cherche à rendre compte de la pertinence de la thérapeutique psychomotrice près d’enfants suivis en pédopsychiatrie, dans l’appropriation des étapes nécessaires à la genèse de la représentation. L’intérêt de la clinique psychomotrice se fonde sur une acceptation de la complexité interrogeant de façon permanente et essentielle les liens entre corps, pensée et relation. La place du psychomotricien dans ce contexte est celle d’être un véritable « sujet médiateur », réceptacle et transformateur de la forme singulière et fondatrice de l’interrelation, celle du dialogue tonique, émotionnel et affectif. C’est dans le soutien et l’élaboration de ce dialogue corporo-psychique, véritable matrice identificatoire, que surviennent les prémices des représentations naissantes, permettant à l’enfant d’accéder progressivement au sentiment « d’être-soi »

Modélisation modale d'une chambre réverbérante par la méthode des éléments finis (caractérisation de la perturbation induite par la rotation du brasseur, application à l'analyse paramétrique des tests statistiques)

Une Chambre Réverbérante (CR) est analysée par la méthode des éléments finis grâce aux programmes Pyfemax et Femlab®, les meilleures techniques étant mises en œuvre pour extraire les modes. On montre que la rotation du brasseur entraîne un balayage fréquentiel (estimé grâce à une procédure de suivi des modes) et une déformation des vecteurs propres, laquelle est caractérisée. Ensuite le champ total est calculé en implémentant les pertes via un facteur de qualité global, cette décomposition modale étant validée par comparaison à la méthode harmonique. Puis sont présentés dans le détail les critères statistiques, et une nouvelle modélisation de la CR en basses fréquences est introduite. Nous montrons aussi que l amélioration de l uniformité du champ lors de la rotation du brasseur est due au recouvrement modal, au balayage fréquentiel et la déformation modale. En application, l efficacité de deux brasseurs est comparée en prenant comme seul critère celui concernant la déformation modaleA Reverberation Chamber (RC) is modelled by Finite Element Method. For each stirrer position, the modes are extracted using state-of-the-art techniques implemented in Pyfemax and Femlab® programs. Then a mode tracking procedure is developed to estimate the frequency sweep induced by the stirrer rotation. Furthermore, the perturbation of the eigenfield is showed and characterized. Before studying the incidence of this modal distortion on the field uniformity, the losses are implemented in the modal expansion (via a user-defined quality factor) and this technique is validated by performing a direct harmonic modelling. Next, the different statistical criteria are discussed and a model of the undermoded RC is proposed. Finally, we prove that the stirring process is due to the modal overlap, the frequency sweep and the modal distortion. This latter perturbation being satisfactorily characterized, it is solely and successfully employed to compare the efficiency of two stirrersPARIS-EST Marne-la-Vallee-BU (774682101) / SudocSudocFranceF

Météoropathologie (étude de l'influence des conditions atmosphériques sur la santé)

LYON1-BU Santé (693882101) / SudocRENNES1-BU Santé (352382103) / SudocSudocFranceF

Wave chaos techniques to analyze a modeled reverberation chamber

International audienceA Reverberation Chamber (RC) is analyzed with techniques issued from the wave chaos domain. The first 200 modes are determined numerically: their cumulated number is separated into a smooth part, predicted by the Weyl formula, and an oscillating part, interpreted in term of periodic orbits. The technique of the nearest-neighbor spacing distribution is also presented, showing the signature of chaos. Eigenfield distributions are examined for two RC geometries and compared to the Gaussian ideal case. Finally, the notion of avoided crossing is illustrated for an almost chaotic RC, leading to a statement for frequency sweeps induced by the stirrer displacement. To cite this article: G. Orjubin et al., C R. Physique 10 (2009). (C) 2009 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved

Statistical model of an undermoded reverberation chamber

International audienceWeibull distribution is adopted to model the electric field component of a Reverberation Chamber (RC). Its first property is to include the asymptotic laws, such as Rayleigh and exponential, and its main advantage lies in the fact that the Weibull shape parameter enables a model of the departure from overmoded to undermoded RC regime. Applications are given, such as an RC modal finite element modeling and a Monte Carlo simulation: they prove that the Weibull two-parameter distribution correctly models the quality factor influence. Moreover, the relevance of the use of this extreme value distribution is illustrated

Chaoticity of a Reverberation Chamber Assessed From the Analysis of Modal Distributions Obtained by FEM

International audienceWave chaos theory is used to study a modeled reverberation chamber (RC). The first 200 modes of an RC at a given stirrer position are determined by the finite element method, and the Weyl formula is checked for various RC geometries, from integrable to chaotic. The eigenfrequency spacing distribution varies according to the degree of ray chaos in the RC related to its geometry. The eigenmode distributions are also analyzed and compared to the theoretical Gaussian distribution: close to the lower useable frequency, the modes of the studied chaotic RC fairly respect this asymptotic property. A general result of chaotic systems is illustrated: when perturbed by the stirrer rotation, the resonant frequencies of an RC avoid crossing. This means that the frequency sweeps tend to vanish at high frequency

Cavity losses modeling using lossless FDTD method

International audienceThe impulse response of a lossless resonant system, usually obtained using the finite-difference time-domain method, permits us to determine the resonant frequencies through the Fourier transform. However, the obtained spectrum has no physical meaning since the losses have not been implemented. Rather than modeling physically the losses, we propose to apply a specific time-domain window to the already simulated signal of the lossless system. This Losses window depends on a user-defined quality factor. The advantage of this postsimulation losses implementation is a capability of parametric study of composite losses. Losses of various physical origins are found for example in the case of reverberation chambers