Determination of the topological charge of a twisted beam with a Fresnel bi-prism

International audienceThe self-interference pattern of a Laguerre Gaussian beam using a Fresnel bi-prism is shown to be very different from what could be expected from a usual laser beam. Actually it resembles the interference pattern that could be obtained using a double slit experiment. The interferences are shifted and the topological charge and its sign can be readily determined considering the shift order of the pattern only. However, since there is no diffraction nor absorption loses unlike in a double slit interference, such a set up could be used even for low power twisted beams or beams with high topological charge. Even fractional topological charges could be determined with an absolute precision of 0.05

Amélioration de l'estimation de la SER de cibles étendues par une approche champ proche

National audienceCet article présente une nouvelle méthode d'estimation de la Surface Equivalente Radar (SER) d'objets de grandes dimensions en milieu réaliste et prenant en compte la problématique champ proche par l'utilisation de la fonction de Green dyadique. Les simulations ont été réalisées sur des cibles métalliques de grandes dimensions placées de 0 à 10 km du radar, pour des fréquences comprises entre 1 et 20 GHz

Transfer of orbital angular momentum on a macroscopic object in the UHF frequency band

International audienceWe report on the exchange of orbital angular momentum between an electromagnetic microwave and a macroscopic object. Using a quadrupole wire antenna at frequency f = 870 MHz, we induce a torque on a suspended copper strip. The induced torque on the strip is of the order of 10 8 Nm. A linear dependence of the acceleration of the strip on the radiated power, up to 8.10-4 °/s², is observed and rotations of a few degrees are measured

Amélioration de l'estimation de la SER de cibles étendues par une approche champ proche

National audienceCet article présente une nouvelle méthode d'estimation de la Surface Equivalente Radar (SER) d'objets de grandes dimensions en milieu réaliste et prenant en compte la problématique champ proche par l'utilisation de la fonction de Green dyadique. Les simulations ont été réalisées sur des cibles métalliques de grandes dimensions placées de 0 à 10 km du radar, pour des fréquences comprises entre 1 et 20 GHz

Use of dyadic Green's function for RCS estimation of large targets

International audienceThis paper presents a new method to estimate the Radar Cross Section (RCS) of a large object in its environment. This estimation method is based on the use of dyadic Green's function method which includes near-field issues. Simulations have been made on perfect electrically conducting (PEC) targets in a frequency band between 1 to 20 GHz. Some simulated results of RCS estimation of a PEC target taking into account the sea effect, are also presented here

Improvement of RCS estimation of large targets by using near-field approach

International audienceThis paper presents a new method in order to estimate the Radar Cross Section (RCS) of large objects in their environments. Object is defined as a volumetric surface and will be considered as a metallic target at a finite distance. This estimation is based on the use of dyadic Green's function method which includes near-field issues. Simulations have been made in a frequency band between 1 to 20 GHz. Some simulated results of RCS estimation of a large metallic target taking into account the sea effect, are presented

Transfert de moment angulaire orbital d'une onde EM à un objet macroscopique dans la bande UHF

National audienceUne onde électromagnétique (EM) est définie par son amplitude, son vecteur d'onde, sa fréquence et son moment angulaire. Ce dernier peut être décomposé en deux parties distinctes [1] : le moment angulaire de spin qui correspond à la polarisation de l'onde, et le moment angulaire orbital (OAM) qui est associé à la distribution spatiale (amplitude et phase) du champ électrique. Ainsi, une onde EM portant de l'OAM est caractérisée par une dépendance azimutale de sa phase notée e-jlθ, avec l, un entier appelé " charge topologique " et correspondant au nombre de rotation de la phase par longueur d'onde, et θ, l'angle d'azimut. De plus, la distribution de la phase induit une interférence destructrice sur l'axe du faisceau, créant un vortex. D'un autre coté, un échange de moment angulaire mène généralement à la création d'un couple mécanique. Une onde EM pouvant porter un tel moment, elle peut donc induire un couple. Ce phénomène a déjà été observé, dans le cas du moment angulaire de spin, que ce soit à l'échelle macroscopique en optique [2,3] et en micro-ondes [4], ou à l'échelle microscopique, en optique uniquement [5]. Dans le cas de l'OAM, cet échange n'a été jusqu'à présent mis en évidence qu'en optique, et à l'échelle microscopique [6]. Le but de cette étude est donc de quantifier les échanges entre une onde EM portant de l'OAM et un objet macroscopique, en micro-ondes, à la fréquence f = 870 MHz

Vectorial characterization of DVB-T propagation channel - Application to radio-Mobile communications : the CAVITE Project

International audienceIn this paper, the whole project CAVITE is described. This project is proposed within the framework of sets of themes around "Sciences and Technologies of Information and Communication" for radio-mobile digital communication in order to increase the data rate or quality of transmission. One of the objectives is the reception of Digital Video Broadcasting on Terrestrial networks (DVB T) in vehicular condition (car, train ...)

Examining slit pore widths within plasma-exfoliated graphitic material utilising Barrett–Joyner–Halenda analysis

Plasma-exfoliated multilayer graphitic material (MLG) consists of orderly aligned stacks which contain many partially oxidised graphitic layers. Slit pores are present between successive stacks and their presence allows for improved friability, facile dispersion and accessibility for the intercalation of compounds. Whilst much research exists into the synthesis and application of MLG, there is a lack of quantitative data regarding their porous structures. This report outlines the structure of MLG as well as the application of Barrett–Joyner–Halenda (BJH) analysis to estimate the distance between adjacent stacks of orderly aligned graphitic layers within MLG. It was found that the distance between stacks can vary quite substantially between 2–131 nm within these plasma-derived materials, correlating with the width of meso- and macro-slit pores. Furthermore, t-plot data also suggests that micropores, likely to exist in the form of both slit pores and in-plane pores, are present within the material, hence stack separations may also exhibit distances of <2 nm. Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM) and X-ray Diffraction (XRD) were used to assist in this interpretation and to correlate with the BJH analysis. MLG was further analysed using Transmission Electron Microscopy (TEM), Brunauer–Emmett–Teller (BET) and t-plot analysis, X-ray Photoelectron Spectroscopy (XPS) and Raman spectroscopy to gain a comprehensive understanding of the material investigated. The above techniques provided results which were consistent with the BJH porosity analysis, thus establishing it as a straightforward and highly effective method for understanding materials with broad pore distributions such as MLGs