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Recently, space-time plasma-steering source has been proposed as an innovative microwave plasma source to meet the challenge of controlling plasmas in overmoded cavities. This concept has been successfully demonstrated experimentally, allowing the space-time control of nanosecond microwave plasmas on initiators. This paper gives insights into the path that shall be taken to reach full space-time control of plasmas in overmoded cavities. To that end, a key criterion, namely the “plasma-steering criterion,” is introduced and verified with a numerical model. This criterion must be respected for an accurate space-time control of plasmas in overmoded cavities. The usefulness of the plasma density (depending on its value with respect to the critical plasma density) on the plasma-control capabilities is also highlighted.

International audience; The high demand for an alternative ignition system for air breathing engines has motivated lot of innovative studies in the last decades. The present paper discusses the results of kerosene droplet ignition with a waveguide based resonant cavity. We show that with this kind of setup, the needed power (injected in the cavity) required to ignite kerosene droplets (with diameter 130 µm) is as low as 4.5 W, depending on the gap size.

International audience; The aim of this paper is to present the promising outlooks that lies ahead for the innovative plasma source we introduced recently. The idea of this source is to dynamically control the plasma location by changing the waveform of the transmitted signal to an overmoded cavity. It is then the behavior of the waves inside the cavity that dynamically control the plasma location, hence the name of Space-Time Plasma Steering Source. Since its introduction in 2019, we have produced three main papers, aimed at different scientific communities: applied physics, physics of plasma, signal processing and mathematical and numerical methods. An overview of these works is first presented in this paper. Then, the promising outlooks for this unusual plasma source are identified and classified into four domains, among which the most important and essential one being the unhooking of the plasmas from the initiators in order to control their location anywhere in the cavity. Several solutions for this “unhooking issue” are then proposed, the most straightforward one being the use of non-intrusive probes.

In the present paper, a detailed investigation of the spatio-temporal dynamics of the recently developed time reversal microwave plasma source is presented. This novel source allows to ignite a plasma at a desired location in a reverberant cavity by focusing the electromagnetic energy in time and space. An important feature is the possibility to control the plasma position only by changing the input microwave waveform. The source is operated in a repetitive pulsed mode with very low duty cycle (typically 5 × 10−2%). Nanosecond pulses have rise time lower than 1 ns. The generated plasmas have typical sizes in the millimeter range and are observed using imaging for dozens of nanoseconds. The plasma behavior is investigated for different pressures and repetition frequencies. A strong dependence is observed between each discharge pulse suggesting the existence of an important memory effect. The latter is probably due to argon metastable atoms and/or residual charges remaining in the post-discharge and allowing the next breakdown to occur at a moderate electric field.

International audience; This paper proposes an improved algorithm, based upon an explicit finite difference scheme, in order to simulate the plasma breakdown induced by a monochromatic High Power Micro-Wave (HPM). The 3D coupled Maxwell–plasma equations are to be solved. We want to study with this model the geometry of the discharge and plasma formation at high pressure which may contribute to shield microwave sensors or circuits. Generally, the simulation of this kind of problem is very time-consuming, but by using the fact that the plasma evolution in time is slow relatively to the monochromatic source period, we can drastically reduce the simulation time. By considering this assumption, we describe in the paper a process which allows to obtain this important reduction. Finally, an example where we show the gain obtained in terms of computation time with our process is given to validate and illustrate the global work.

International audience; This paper details the work of the LAPLACE Electromagnetism Research Group to develop an original measuring setup dedicated to the detection of an EMDrive like force. Recent peer-reviewed experimental results [1, 2] were obtained using similar setups based on a torsion pendulum combined with an optical sensor. These very accurate measurement setups are appropriate for measuring such an extremely weak force. They also appear costly, which may discourage other research teams from working on this topic. Our main goal is then to provide an alternative configuration, based on a commercial precision balance, in order to build a measuring setup more affordable, handy, and accurate enough to measure an EMDrive like force. Our experimental system is capable of feeding a truncated cone shaped 2.45 GHz resonant cavity with power up to 140 W. To calibrate the EMDrive force and avoid false positive thrusts, an original setup has been proposed and evaluated. It allows us to really consider that the parasitic effects do not alter the hypothetical force measurement by the use of force direction switching during the measurement.

At radio frequencies, previous works by Mohammadi et al. derived from quantum mechanics state that the spin angular momentum (SAM), orbital angular momentum (OAM), and their sum [the total angular momentum (TAM)] can be estimated locally without ambiguity. In this letter, we highlight an inconsistency in this method when adding an SAM with an OAM. The latter cannot be estimated for a nonzero SAM. From optical currents, we propose a more general method. It is based on the Poynting expansion into spin and orbital components to estimate the OAM regardless of the SAM value.

The radiation of a series gap in a coplanar waveguide (CPW) line has been studied for Ku band applications. While theoretical models usually describe accurately the capacitance of the gap, they fail to include the radiation loss. This paper shows that it is a relevant phenomenon in Ku Band when the width of the line is close to 1mm and low precision etching is employed (low cost printing technology). Additionally, a technique for the reduction of such losses is presented and evaluated.

This paper addresses the RF link budget of a communication system using unusual waves carrying an orbital angular momentum (OAM) in order to clearly analyse the fundamental changes for telecommunication applications. The study is based on a typical configuration using circular array antennas to transmit and receive OAM waves. For any value of the OAM mode order, an original asymptotic formulation of the link budget is proposed in which equivalent antenna gains and free-space losses appear. The formulations are then validated with the results of a commercial electromagnetic simulation software. By this way, we also show how our formula can help to design a system capable of superimposing several channels on the same bandwidth and the same polarisation, based on the orthogonality of the OAM. Additional losses due to the use of this degree of freedom are notably clearly calculated to quantify the benefit and drawback according to the case., Comment: 33 pages, 11 figures

International audience; This paper presents a discussion about the RF link budget for a communication system based on unusual waves carrying a non-zero orbital angular momentum (OAM). A typical configuration using circular antenna arrays of isotropic sources to transmit and receive OAM waves is considered. We point out issues when usual assumptions are made to express the link budget. Then, we propose to express the power budget associated with OAM in an elementary MIMO matrix approach. Using a single mode communication configuration, some basic numerical calculations and case studies based on the developed formulations can then be led and discussed, highlighting some intrinsic limitations. Indeed, the asymptotic behavior of the link budget leads to question the concepts of gain and propagation losses.

International audience; This paper presents an experimental setup for the wideband RF characterization of plasma Micro Hollow Cathode Sustained Discharge (MHCD). This microdischarge is studied as a candidate for integrated active component in antennas, using the change of permittivity caused by the presence of plasma. The measurement setup consists of a 50 Ω microstrip line with a single MHCD placed in its center. The measurement of the scattering parameters of the experimental device permits the evaluation of the complex permittivity and conductivity of the MHCD.

A growing interest has been given to reconfigurable antennas. Most of these antennas rely on the integration of switch technologies. In this paper, it is proposed to test the integration of a set of commercially available MEMS switches in a PCB circuit design. The components are inserted in the slots of a CPW line enlarged by a large bandwidth multi section impedance transformer. This integration test is considered as a first and necessary step towards the design of reconfigurable antennas.

Les îles du Pacifique sont célèbres pour le très haut niveau d'endémisme et la grande vulnérabilité de leurs faunes et de leurs flores. Bien que la valeur scientifique et patrimoniale des écosystèmes du Vanuatu ait conduit à classer ce pays comme « point chaud » de la biodiversité, l'archipel souffre d'un déficit de connaissances en comparaison avec d'autres archipels du Pacifique Sud. L'expédition Santo 2006 sur l'île d'Espiritu Santo a eu pour but d'inventorier les faunes et les flores marines, terrestres et dulçaquicoles de cette île, en portant un accent particulier sur les compartiments négligés de la biodiversité. Tous les milieux, depuis les grands fonds marins au large de l'île jusqu'aux récifs, grottes, rivières, forêts et montagnes ont été inventoriés. Des échantillons de tissus biologiques, des enregistrements de sons et des photos numériques des organismes vivants ont complété les prélèvements d'organismes complets. Une attention particulière a été portée aux espèces introduites et invasives, afin d'établir un état de référence de la biodiversité de Santo en ce début du xxie siècle. L'expédition a impliqué sur le terrain plus de cent cinquante scientifiques, bénévoles et étudiants de vingt-cinq pays. The islands of the Pacific are famous for the high levels of endemism of their flora and fauna, and also the high levels of threats on their faunas and floras. Although Vanuatu is ranked as a biodiversity 'hotspot' under many global analyses, the country suffers from a deficit in scientific knowledge on its biota compared to other South Pacific island groups. The goal of the Santo 2006 expedition on the island of Espiritu Santo was to document the marine, freshwater, and terrestrial species of plants and animals living on or around the island, with a focus on the neglected components of biodiversity. All major environments have been sampled, from deep offshore sea bottoms to coral reefs, caves, rivers, forests and mountains; tissue clips, sound records and digital images supplement samples of dried or preserved specimens. In order to establish a baseline inventory of the biodiversity of Santo, special attention was given to introduced and invasive species. Field work involved over 150 scientists, volunteers and students from 25 countries.

International audience; A novel multi-band circular polarization antenna based on pyramidal structure and trap-loads was designed and tested experimentally. The measured Sparameters of trap-loads have been taken into account in the design for obtaining the technical requirements of the antenna. The measurement results confirm the tri-band behavior of the antenna in the GPS/Galileo and TM MicroSat frequency bands. The proposed radiating structure can also be adapted to combine other satellite applications, like S-band Digital Multimedia Broadcasting.

International audience; There is a constant increase of interest for multi-band antennas, mainly driven by the objective to reduce the number of onboard and ground antennas by integrating several applications on a single radiating element. In the framework of the Galileo satellite navigation system, the French Space Agency (CNES) proposed to study the possibility of combining GPS, Galileo and MicroSat telemetry (TM) applications on the same multi-band antenna. The GPS / Galileo bands used here include for example ARNS as well as high precision applications. This communication introduces a novel topology of trap-loaded multi-band antenna based on pyramidal structures [1]. The experimental results confirm the good performances observed during the electromagnetic simulations. The multi-band behavior and the required circular polarization characteristic of the proposed pyramidal antenna are validated experimentally.

es travaux de recherche visent au développement de modèles électromagnétiques pour les systèmes et les canaux de transmission de l'aéronautique. Une des originalités est l'utilisation d'ondes élémentaires pour lesquelles existent des formulations analytiques et des décompositions. Les modèles développés reposent également sur des approximations physiques pertinentes et ils tiennent compte des spécificités de domaines d'applications souvent en lien avec l'aéronautique.Cette présentation fera une synthèse de ces activités en partant des modèles les plus généraux pour arriver à ceux tenant compte de la configuration et du système étudié. Cette démarche permettra également de refléter les différentes échelles des problèmes traités en allant de l'élémentaire (un élément d'un système RF) vers l'étude d'une scène de propagation complète. Seront successivement abordés les méthodes de différences finies pour les dispositifs RF, les méthodes de faisceaux gaussiens pour les radômes et les systèmes quasi-optiques, les liaisons par ondes à moment angulaire orbital, et les canaux de transmission multi-trajets des systèmes de navigation aéronautique GNSS et VOR.

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Electromagnetic periodic structures are of great interest. These structures act as frequency filters and allow the manufacturing of meta-materials which appear to be composite and artificial. They exhibit electromagnetic properties that are unusual to natural materials such as band gaps. This allows new devices to guide, focus or stop the propagation. This is for example useful to avoid coupling between various radiating elements via the characterization of the surface waves which propagate at the interface between air and the periodic structure. This thesis provides a description of the finite element method dedicated to the characterization of periodic structures. Numerical modelling results in eigenvalue problems of large sizes. It involves solving linear systems compounds of sparse matrices. A method is therefore discussed for solving this type of problem, optimizing and combining different algorithms. Before discussing the different aspects of the developed method, we establish an exhaustive list of all the existing methods by stating their advantages and drawbacks. We note that the finite element method can handle a wide range of periodic structures in three dimensions without limitation on their shape. We present different formulations of this method. Then the algorithmic aspects of the method are detailed. We show that an analysis of the resolution settings can impact the physical interpretations of the results. Finally we show the performance of our tool on classical validation results from the bibliography and we discuss the characterization of surface waves. Therefore, the study of a patch antenna array included in metal cavities is conducted. To conclude we can say that the studies conducted in this thesis have resulted in the production of a code used in an environment calculation initially present at ONERA.; En électromagnétisme les structures périodiques suscitent un grand intérêt. Ces structures agissent ainsi comme des filtres fréquentiels et permettent la fabrication de méta-matériaux, composites et artificiels. Elles présentent des propriétés électromagnétiques inédites pour les matériaux naturels telles que des bandes interdites. On a ainsi pu fabriquer de nouveaux dispositifs permettant de guider, de focaliser ou de stopper la propagation. C'est par exemple utile pour éviter le couplage entre différents éléments rayonnants notamment via la caractérisation des ondes de surface qui se propagent à l'interface entre l'air et la structure périodique. Ce travail de thèse s'inscrit dans ce contexte et propose une description de la méthode des éléments finis dédiée à la caractérisation des structures périodiques. La modélisation numérique aboutit à des problèmes de valeurs propres de grandes tailles. Elle implique la résolution de systèmes linéaires composés de matrices creuses. Une méthode est abordée pour résoudre ce type de problème, en optimisant et combinant différents algorithmes. Avant d'aborder les différents aspects de la méthode développée, nous établissons une liste exhaustive de l'ensemble des méthodes qui existent en énonçant leurs avantages et leurs inconvénients. Nous constatons notamment que la méthode des éléments finis permet de traiter un large éventail de structures périodiques en trois dimensions sans limitation sur leur forme géométrique. Nous présentons alors les différentes formulations de cette méthode. Ensuite les aspects algorithmiques de la méthode sont détaillés. Nous montrons notamment qu'une analyse des paramètres de résolution permet de préciser les interprétations physiques des résultats obtenus. Finalement nous présentons les performances de notre outil sur des cas d'applications issus de la littérature et nous abordons la caractérisation des ondes de surface. Pour cela, l'étude d'un réseau d'antennes patchs insérées dans des cavités métalliques est conduite. Notons pour conclure que les études conduites au cours de cette thèse ont abouti à la production d'un code utilisable dans un environnement de calcul initialement présent à l'ONERA.

Electromagnetic periodic structures are of great interest. These structures act as frequency filters and allow the manufacturing of meta-materials which appear to be composite and artificial. They exhibit electromagnetic properties that are unusual to natural materials such as band gaps. This allows new devices to guide, focus or stop the propagation. This is for example useful to avoid coupling between various radiating elements via the characterization of the surface waves which propagate at the interface between air and the periodic structure. This thesis provides a description of the finite element method dedicated to the characterization of periodic structures. Numerical modelling results in eigenvalue problems of large sizes. It involves solving linear systems compounds of sparse matrices. A method is therefore discussed for solving this type of problem, optimizing and combining different algorithms. Before discussing the different aspects of the developed method, we establish an exhaustive list of all the existing methods by stating their advantages and drawbacks. We note that the finite element method can handle a wide range of periodic structures in three dimensions without limitation on their shape. We present different formulations of this method. Then the algorithmic aspects of the method are detailed. We show that an analysis of the resolution settings can impact the physical interpretations of the results. Finally we show the performance of our tool on classical validation results from the bibliography and we discuss the characterization of surface waves. Therefore, the study of a patch antenna array included in metal cavities is conducted. To conclude we can say that the studies conducted in this thesis have resulted in the production of a code used in an environment calculation initially present at ONERA.; En électromagnétisme les structures périodiques suscitent un grand intérêt. Ces structures agissent ainsi comme des filtres fréquentiels et permettent la fabrication de méta-matériaux, composites et artificiels. Elles présentent des propriétés électromagnétiques inédites pour les matériaux naturels telles que des bandes interdites. On a ainsi pu fabriquer de nouveaux dispositifs permettant de guider, de focaliser ou de stopper la propagation. C'est par exemple utile pour éviter le couplage entre différents éléments rayonnants notamment via la caractérisation des ondes de surface qui se propagent à l'interface entre l'air et la structure périodique. Ce travail de thèse s'inscrit dans ce contexte et propose une description de la méthode des éléments finis dédiée à la caractérisation des structures périodiques. La modélisation numérique aboutit à des problèmes de valeurs propres de grandes tailles. Elle implique la résolution de systèmes linéaires composés de matrices creuses. Une méthode est abordée pour résoudre ce type de problème, en optimisant et combinant différents algorithmes. Avant d'aborder les différents aspects de la méthode développée, nous établissons une liste exhaustive de l'ensemble des méthodes qui existent en énonçant leurs avantages et leurs inconvénients. Nous constatons notamment que la méthode des éléments finis permet de traiter un large éventail de structures périodiques en trois dimensions sans limitation sur leur forme géométrique. Nous présentons alors les différentes formulations de cette méthode. Ensuite les aspects algorithmiques de la méthode sont détaillés. Nous montrons notamment qu'une analyse des paramètres de résolution permet de préciser les interprétations physiques des résultats obtenus. Finalement nous présentons les performances de notre outil sur des cas d'applications issus de la littérature et nous abordons la caractérisation des ondes de surface. Pour cela, l'étude d'un réseau d'antennes patchs insérées dans des cavités métalliques est conduite. Notons pour conclure que les études conduites au cours de cette thèse ont abouti à la production d'un code utilisable dans un environnement de calcul initialement présent à l'ONERA.

Focus on synanthropic mammals