An asymmetry detected in the disk of Kappa CMa with the AMBER/VLTI

International audienceAims. We study the geometry and kinematics of the circumstellar environment of the Be star Kappa CMa in the Br gamma emission line and its nearby continuum. Methods. We use the VLTI/AMBER instrument operating in the K band which provides a spatial resolution of about 6 mas with a spectral resolution of 1500 to study the kinematics within the disk and to infer its rotation law. In order to obtain more kinematical constraints we also use an high spectral resolution Pa beta line profile obtain in December 2005 at the Observatorio do Pico do Dios, Brazil and we compile V/R line profile variations and spectral energy distribution data points from the literature. Results. Using differential visibilities and differential phases across the Br gamma line we detect an asymmetry in the disk. Moreover, we found that kappa CMa seems difficult to fit within the classical scenario for Be stars, illustrated recently by alpha Arae observations, i.e. a fast rotating B star close to its breakup velocity surrounded by a Keplerian circumstellar disk with an enhanced polar wind. Finally we discuss the possibility for kappa CMa to be a critical rotator with a Keplerian rotating disk and try to see if the detected asymmetry can be interpreted within the "one-armed" viscous disk framework

Commutateurs MEMS et leurs applications aux filtres accordables fort Q

Les systèmes de télécommunications actuels proposent de plus en plus de fonctionnalités ce qui rend leurs architectures électroniques plus complexes et plus encombrantes. Pour palier ce problème, il est proposé d'intégrer des composants reconfigurables, capables de s'adapter à la fréquence de travail de chaque application. Les MEMS RF (Micro Electro-Mechanical Systems) garantissent cette agilité en fréquence au même titre que les composants semi-conducteurs mais présentent de meilleures performances et ne consomment pas de puissance. Dans le cadre de cette thèse, il est présenté la conception et la réalisation de commutateurs MEMS RF et leur intégration dans des filtres afin de les rendre accordables.Today telecommunication systems are proposing more and more functionality leading to more bulky and more complex electronic architectures. In order to solve this problem, it has been proposed to integrate reconfigurable components able to adapt to the application frequency. As for solid state devices, RF MEMS (Micro Electro-Mechanical Systems) guarantee this frequency agility but are presenting better performances and have lower power consumption. In this thesis, the design and fabrication of RF MEMS switches and their integration into filters in order to make them tuneable, is presented.LIMOGES-BU Sciences (870852109) / SudocSudocFranceF

Compact 2-Pole and 4-Pole 1.5-0.9 GHz Constant Absolute Bandwidth Tunable Filters

International audienc

High-Q 3D Tunable RF MEMS Filter with a Constant Fractional Bandwidth

International audienc

Compact 2-Pole and 4-Pole 2.4-2.8 GHz Dual-Mode Tunable Filters

International audienc

Filtres compacts 2 pôles et 4 pôles, accordables de 2.4 à 2.8 GHz pour des applications à bande fractionnaire constante

National audienc

Miniature RF MEMS Metal-Contact Switches for DC-20 GHz Applications

International audienceThis paper presents the design and measurements of a miniature RF MEMS (Micro-Electro-Mechanical System) metal-contact switch. The dimensions (25×24 × 1.6 μm) and shape of the beam and actuation pad have been optimized to result in a 12-25 μN contact force at 52-60 V actuation, with a corresponding restoring force of 15 μN. Measured S-parameters on a single switch show an up-state capacitance of 5 fF and a 13-14 Ω contact resistance for a Au-Ru contact under an actuation voltage of 55 V. In order to reduce the effective switch resistance, 10 miniature RF MEMS switches have been placed in parallel and result in an up-state capacitance of 30 fF and a switch resistance of 1.4 Ω. The measured switching time is 2.2 μs and the release time is <;1 μs. The switch is robust to stress effects (residual and stress gradients) which increases its yield on large wafers. To our knowledge, this is the first demonstration of a miniature RF-MEMS metal-contact switch and with an excellent figure-of-merit (fc=1/(2.π.Ron.Cu)=3.8 THz)

Miniature MEMS switches for RF applications

International audienceThis paper presents a new way to design MEMS (microelectromechanical system) metal contact switches for RF applications using miniature MEMS cantilevers. A single 25 × 25 μm switch is first demonstrated with a Au-to-Ru contact, Cu = 5 fF and Ron = 7 Ω at an actuation voltage of 55 V. The measured switching time is 2.2 μs and the release time is <;1 μs. The switch is robust to stress effects (residual and stress gradients) which increases its yield on large wafers. To reduce the effective switch resistance, 10-20 miniature RF MEMS switches have been placed in parallel and result in equal current division between the switches, an up-state capacitance of 30-65 fF and a down-state resistance of 1.4-1.5 Ω. Furthermore, 10-20 element back-to-back switch arrays are developed and result in a marked improvement in the reliability of the overall switching device. A series-shunt design is also demonstrated with greatly improved isolation. The device has a figure-of-merit of fc = 1/(2πRonCu) = 3.8 THz (RonCu = 42 fs)

High Power Handling Low-Voltage RF-MEMS Switched Capacitors

International audienc