Gerard Labaune

Field penetration through composite material using FDTD method

Field penetration through a composite material is investigated by solving the curl Maxwells equation with the finite difference method. Use is made of the FDTD (finite-difference time-domain) code ALICE for current injection. The structure used to study field penetration is a perfectly conductive parallelepiped cavity with a square aperture on the upper side. A current injection technique with a thin conductive wire allows electromagnetic distributions outside and inside the cavity to be obtained. Analytical results are presented and discussed.<<ETX>>

Rôle de l’arc transitoire dans le rayonnement des ondes métriques et décimétriques de l’éclair

AnalyseL’auteur suppose que l’émission électromagnétique de l’éclair des ondes métriques et décimétriques est due à la phase d’arc transitoire dans le mécanisme d’ionisation de l’air vierge. Un calcul du champ rayonné par la formation d’un plasma dans l’air à la pression atmosphérique est comparé aux résultats expérimentaux obtenus sur l’éclair réel. La très bonne concordance des résultats nous permet de supposer que les mécanismes d’arc transitoire sont responsables de l’émission de l’éclair.AbstractThe author assumes that the electromagnetic radiation in the VHF-UHF range associated with lightning is due to the transient arc phase in virgin air ionization process. Theoretical calculation of electromagnetic radiation of plasma formation in the air at atmospheric pressure is compared to experimental results on lightning. The close correlation between these results leads to associate vhf-uhf radiation of lightning to the transient arc phase.

Penetration of electromagnetic waves through loaded apertures

A method for investigating the penetration of electromagnetic waves through loaded apertures is presented based on a direct calculation of the equivalent magnetic current distribution in the aperture plane. The advantages of this method are that any shape of the aperture can be introduced in the model and that a contact impedance between the loading material and the structure can be taken into account. The source of excitation is arbitrary. Examples showing the relative importance of the contact impedance for various types of excitation are given.<<ETX>>

Comparison of experimental and numerical results for transient electromagnetic fields induced on a scale model aircraft by current-injection technique

A scale model of the Transall C160 military aircraft, 1/10 of the actual, was installed above a large copper ground plate and connected to it. The entry point at the nose was hard-wire connected to a 12- mu F/5-kV capacitor bank, and the current pulse launch was made using a triggered atmospheric-pressure spark gap. The exit point at the tail or at the left wing tip, depending on the configuration, was connected to the ground plate via an 80- Omega waveshaping resistor. The transient electromagnetic fields on the outer skin of the model were measured using D-dot and B-dot sensors. Three D-dot sensors were mounted on the forward upper fuselage, on the top and the bottom of the left wing. Two B-dot sensors were mounted on the forward upper fuselage and on the top of the left wing. The current was also measured using three i-dot sensors mounted on the nose boom, on the left wing tip, and on the tail boom. A comparison of experimental and computed electromagnetic fields on the scale model was performed for two experimental configurations of current injection: nose to tail and nose to left wing. As shown for one typical case, all the data were predicted with excellent frequency agreement and very good amplitude agreement.<<ETX>>

Décharges diélectriques et perturbations électromagnétiques sur satellites géostationnaires

RésuméDe nombreuses anomalies de fonctionnement ont été observées sur satellites géosynchrones. Elles sont attribuées à des décharges électrostatiques survenant sur les revêtements isolants à la surface du satellite, en particulier lors des périodes d’orages magnétiques. Le satellite est un corps électriquement flottant qui se décharge en émettant dans l’espace un nuage d’électrons. Ce phénomène d’expansion électronique constitue la spécificité du problème électromagnétique sur satellite. Celui-ci se pose en termes nouveaux nécessitant une description précise du processus de décharge.AbstractVarious operational anomalies on satellites in geosynchronous orbit, chiefly occurring during magnetic storms are attributed to spacecraft charging. The build up of static charges on the surfaces of the spacecraft leads to various breakdown processes. Self-sustained discharges, characterized by a strong electrons emission out of the material, may occur on negatively charged films of polymer used, for example, as thermal blankets. The so-called blowoff emission is an important source of perturbation through a complex interaction of the electromagnetic field with the spacecraft, the description of which needs a precise knowledge of the breakdown mechanism.

Calcul et mesure de I’efficacité de blindage des matériaux composites

RésuméLe problème étudié est celui de la diffraction d’une onde électromagnétique par une ouverture pratiquée dans un plan métallique. On s’intéresse à une ouverture libre ou obstruée par un panneau résistif relié au plan par un joint imparfait. Du point de vue théorique, les résultats approchés déduits du formalisme des dipôles équivalents sont complétés par la résolution exacte du problème au moyen d’une nouvelle équation intégrate. La validation expérimentale des modèles est conduite à l’aide d’une celluletem dont l’électrode de retour est munie d’une ouverture. L’application de la méthode conduit à la détermination expérimentale des propriétés électromagnétiques de plusieurs échantillons de matériaux en tenant compte de l’influence des joints.AbstractWe study the scattering of an electromagnetic wave by an aperture in a metallic plane. We consider both cases of free aperture and aperture loaded by a finite conductivity material connected to the plane by any joint. Theoretically, results derived from theequivalent dipole formalism are completed by the resolution of a new integral equation. Experimental comparison with our results is presented using atem cell of which the external electrode is provided with an aperture. The use of this method leads to the experimental definition of electromagnetic properties of several samples taking into account the effect of the joint.