Modélisation EM haute fréquence d'arbre pour l'imagerie SAR haute résolution

International audienceDans ce travail, nous nous intéressonsà l'élaboration d'un modèleélectromagnétique d'arbre réaliste, adaptéà l'imagerie radar haute fréquence et haute résolution. Cette premièreétape viseàétablir une modélisation de référence qui permettra dans un second temps l'élaboration d'un modèle approché exploitable pour des scènes de grandes dimensions. Ce premier modèle est réalisé en deux temps. Tout d'abord, la réalisation d'une représentation 3D est faiteà partir de logiciels de modélisation graphique. Ensuite, le maillage généré est exploité pour calculer la visibilité ainsi que la réflectivité des différents contributeurs du signal radar

Q-Band Millimeter-Wave Antennas: An Enabling Technology for MultiGigabit Wireless Backhaul

[EN] The bandwidth demands in mobile communication systems are growing exponentially day by day as the number of users has increased drastically over the last five years. This mobile data explosion, together with the fixed service limitations, requires a new approach to support this increase in bandwidth demand. Solutions based on lower-frequency microwave wireless systems may be able to meet the bandwidth demand in a short term. However, with the small-cell mass deployment requiring total capacities of 1 Gb/s/km2, scalable, multigigabit backhaul systems are required. Millimeter-wave technology fits nicely into these new backhaul scenarios as it provides extended bandwidth for high-capacity links and adaptive throughput rate, which allows efficient and flexible deployment. Besides these advantages, millimeter-wave solutions become even more attractive when the cost of backhaul solutions and the cost of spectrum licenses are factored in. Compared to the cost of laying fiber to a cell base station, which is the only other scalable solution, the millimeter-wave solution becomes the most appropriate approach.The research leading to these results received funding from the European Commission's seventh Framework Programme under grant agreement 288267.Vilar Mateo, R.; Czarny, R.; Lee, ML.; Loiseaux, B.; Sypek, M.; Makowski, M.; Martel, C.... (2014). Q-Band Millimeter-Wave Antennas: An Enabling Technology for MultiGigabit Wireless Backhaul. IEEE Microwave Magazine. 15(4):121-130. https://doi.org/10.1109/MMM.2014.2308769S12113015

Experimental demonstration of metamaterials application for mitigating scan blindness in phased array antennas

This paper presents two metamaterial-inspired solutions to mitigate the scan blindness effects in a phased array antenna. In the first solution, portions of a bed of nails are introduced in the radome to prevent the excitation of surface waves. In the second solution, a superstrate metasurface is designed to synthesize a permittivity tensor optimized to achieve a wide angle impedance matching. In both approaches, the numerical simulations are successfully compared with measurements of a phased array antenna prototype with 100 elements. The wire medium-based solution reveals an effective way for reducing the blind-spot in a wide bandwidth, while the metaradome has been found less suitable for the same purpose.This work was supported by the METALESA project A-1089- RT-GC that was coordinated by the European Defence Agency (EDA) and funded by 11 contributing Members (Cyprus, France, Germany, Greece, Hungary, Italy, Norway, Poland, Slovakia, Slovenia and Spain) in the framework of the Joint Investment Programme on Innovative Concepts and Emerging Technologies (JIP-ICET)

Microscopie ionique a balayage a haute resolution spatiale : obtention simultanee d'images filtrees par un spectrometre de masses a fort pouvoir separateur

SIGLECNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Magnetic excitations in assemblies of dipolar coupled nanoparticles

The equilibrium magnetization configurations and the associated microwave susceptibility spectra of dipolar coupled nanoplatelets are explored using three-dimensional (3D) micromagnetic simulations. First, the case of periodic arrangements of nanoplatelets on square arrays is considered. As a result, a macro-vortex state defined as a flux closure pattern spreading over the whole array with or without a vortex core can be stabilized starting from an initial orthoradial magnetization configuration. For macro-vortex states with a vortex core, the linear excitation spectrum exhibits a sub-GHz resonance line ascribed to the vortex core dynamics at the array center. The features of this line (spectral position and amplitude) depend on the array size and the strength of the dipolar coupling through the interplatelet spacing. This resonance is also observed for macro-vortex states without a vortex core but only in the regime of a strong dipolar coupling. The effect of disorder is then investigated by numerically generating assemblies of nanoplatelets with a position disorder and, shape and size distributions. The micromagnetic simulations reveal flux closure magnetization configurations as well but without a vortex core. A low-frequency resonance appears in the susceptibility spectra for quite high surface contents of nanoplatelets but its amplitude is weaker compared to the case of periodic arrays. This line arises from a collective mode extended over a few nanoplatelets. A large variety of static and dynamical behaviors is thus evidenced resulting in a great complexity even in such model systems

3D Dynamic Micromagnetic Simulations of Susceptibility Spectra in Soft Ferromagnetic Particles

International audienceLes propriétés hautes fréquences de petits éléments ferromagnétiques 3D ont été étudiées l'aide de simulations micromagnétiques. Les spectres de susceptibilité dynamique associés à deux types d'éléments de taille submicrométrique : un plot cylindrique présentant un état vortex et une particule en forme d'oeil présentant un état bidomaine sont reportés. Dans ces structures confinées, les spectres révèlent une riche variété de modes qui sont identifiés

A compact dual polarized 3:1 bandwidth omnidirectional array of spiral antennas

International audienceA circularly polarized wideband omnidirectional array of spiral antennas is presented. It covers the frequency band from 1.2 GHz up to 3.6 GHz while keeping a good S11 and an omnidirectional coverage. This array achieved a dual polarization using left and right hands archimedean spiral antennas. The gain of the array is enhanced using a unique cavity for the entire array and the realized gain is above the maximum theoretical gain of a single spiral antenna

Domain wall resonant modes in nanodots with a perpendicular anisotropy

International audienceThe dynamic susceptibility spectra of ferromagnetic nanodots with a large perpendicular anisotropy exhibiting a two-stripe domain state at remanence are investigated using 3D micromagnetic simulations. Due to the confined geometry, multiple domain wall excitations are revealed within the frequency range 0.1–15 GHz. The size dependence (dot thickness and dot diameter D) of the excitation spectra is reported