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This paper presents efforts made to improve the characterization of electrostatic discharges induced by severe spacecraft surface charging events. The novelty of this work resides in the design and implementation of a test setup that provides more refined information than the techniques usually adopted and prescribed by spacecraft design guidelines. We applied the test setup to two different nanosatellite mockups. By reducing the coupling with ground-test equipment, we significantly improved the measurement precision. An application of such a setup is the evaluation and prediction of inrush currents caused on nanosatellites by electrostatic discharges induced by hazardous space weather conditions.

International audience; Characterization of the electromagnetic field emitted by various sources (antenna, radar, etc.) is an important issue, either for civil or defense applications. The measurement of electromagnetic field may be performed either by local probes or by thermography imaging, in particular with an infrared camera. The latter method, called electromagnetic infrared (EMIR) has been developed several years ago. We have recently successfully implemented this technique in the domain of visible light thanks to the combination of a film sensitive to either electric field (slightly conductive film) or magnetic field (insulating film with ferromagnetic particles) and a polymer coating doped with fluorescent molecules with an emission depending on temperature, indeed a thermofluorescent sensor. We present our recent results obtained imaging the microwave magnetic field emitted in the near field of a zeroth-order resonator (ZOR) antenna. The sensing film is a stack of FLEX-TOKIN magnetic absorber, already tested by EMIR infrared thermography in our group. A 20 µm film composed of a mixture of rhodamine B (RhB) in an epoxy matrix is screen printed on the FLEX surface. RhB, in ethanol solution, has a thermofluorescence coefficient of ∼2%/K at room temperature at its maximum of fluorescence of 595 nm. Excitation light is delivered by an array of blue 470 nm LEDs. The 4.29 GHz microwave excitation of the ZOR device is amplitude modulated at 0.1-0.5 Hz in order to cancel any thermal drift and convection of the thermofluorescence image. Low-frequency excitation modulation also allows noise cancellation via image pixel demodulation postprocessing. We present the deduced temperature mapping of the sensing film placed 2 mm above the ZOR patch antenna.

International audience; Characterization of the electromagnetic field emitted by various sources (antenna, radar...) is an important issue, either for civil or defense applications. The measurement of the electromagnetic field may be performed by a local probe, but the infrared thermography imaging is an alternative way. The latter method, called EMIR [1] (ElectroMagnetic InfraRed) has been used for years in particular at ONERA where it had been developed. We have recently successfully implemented this technique in the domain of visible light, named as EMVI [2]. As in the EMIR method, a thin film (sensitive to either electric field or magnetic field) is heated by the emitted field. But here the film is coated with a polymer doped with fluorescent molecules. As the fluorescent emission depends on the temperature of the film, we get a thermofluorescent sensor. The results presented here illustrate that new method: both magnetic and electric field imaging of a High Impedance Surface (HIS) have thus been obtained.

International audience; The characterization and visualization of the radiated electromagnetic field is a way to diagnose and check microwaves sources, in particular in the space industry. Beyond the traditional 3D scanning of the radiating element, infrared thermography is an alternative way that may give key results in a reduced time, since a few seconds are sufficient to obtain the emitted field map even for a complex multi-cells antenna. This method, called EMIR (ElectroMagnetic InfraRed) has been developed and used for years at ONERA. We have recently extended this technique to the magnetic field, which will lead to a complete characterization of the near field structure. We illustrate this feature in the particular cases of antennas for space application and for a High Impedance Surface (HIS), a metamaterial structure that could be used to reduce the coupling between antennas confined in compact structures (typically size constraints of the spatial components).

International audience; Methods to measure the electromagnetic field intensity on a large scale should be improved to meet the growing demand in civil and military applications. The recent development and an application of a microwave electromagnetic field imaging method using a thermofluorescent device and detection in the visible-light range are described. The sensor is a flexible film sensitive to either an electric field (slightly conductive film) or a magnetic field (insulating film with ferromagnetic particles) coated with a polymer doped with fluorescent molecules displaying temperature-dependent emission. We use a lock-in thermog-raphy protocol consisting of modulation of the field at low frequency, which allows us to suppress the noise due to heat-transfer phenomena and the part of the signal not directly related to field absorption. Two applications of the method are presented: (i) imaging the microwave magnetic field emitted by a resonator antenna and (ii) the local probe measurement of the electric field inside a multibeam antenna. The process to develop the sensitive film, its detailed characterization, and the thermofluorescence-image demodula-tion postprocessing are presented in detail. This approach is much cheaper than one based on infrared thermometry and could permit democratization of microwave-and radio-frequency electromagnetic field imaging.

International audience; Since the beginning of the 20th century a controversy has been continuously revived about the existence of the Zenneck Wave. This wave is a theoretical solution of Maxwell’s equations and might be propagated along the interface between the air and a dielectric medium. The expected weak attenuation at large distance explains the constant interest for this wave. Notably in the High Frequency band such a wave had been thought as a key point to reduce the high attenuation observed in High Frequency Surface Wave Radar. Despite many works on that topic and various experiments attempted during one century, there is still an alternation of statements between its existence and its nonexistence. We report here an experiment done during the optimisation of the transmitting antennas for Surface Wave Radars. Using an infrared method, we visualize a wave having the structure described by Zenneck above a metasurface located on a dielectric slab.

A new microwave magnetic field measurement method based on infrared emission is presented. This method uses thin patterned ferromagnetic films sputtered on polymer substrates. The incident field interacts with the film and is responsible for ferromagnetic losses that create local heating. This heating is recorded by an infrared camera, providing magnetic field pattern images and amplitude evaluation. Moreover, the tangential components of the H field can be identified thanks to the anisotropic structure of the sputtered film. The large permeability NiFe based thin films were grown using a sputtering method and complex permeability measurements have been carried out in the microwave range. Both infrared pictures and magnetic permeability measurements are presented and correlated.

An original method of characterization of high impedance surfaces (HIS) is presented to exhibit electric field patterns. The electric field frames are obtained through a resistive film located in the near field domain of the HIS. The film heating is recorded using an infrared camera and gives after post-processing electric field magnitude profiles. We applied this technique to a HIS specially tuned for reducing mutual coupling in a global navigation satellite systems (GNSS) array designed for the E5 Galileo band. The mushroom-like HIS, designed and realized with the help of simulation, is located near the ground plane of a micro-strip line which allows S parameter characterization. Present measurement enables near field characterization and field structure analysis, and is therefore a complement to usual analysis. Moreover, the technique shows the very special field structure, including sub-lambda details, created by the HIS and more generally by metamaterial structures.

Structural and magnetic properties of epitaxial Co2FeAl Heusler alloy thin films were investigated. Films were deposited on single crystal MgO (001XS) substrates at room temperature, followed by an annealing process at 600 °C. MgO and Cr buffer layers were introduced in order to enhance crystalline quality, and improve magnetic properties. Structural analyses indicate that samples have grown in the B2 ordered epitaxial structure. VSM measures show that the MgO buffered sample displays a magnetization saturation of 1010 ± 30 emu/cm3, and Cr buffered sample displays a magnetization saturation of 1032 ± 40 emu/cm3. Damping factor was studied by strip-line ferromagnetic resonance measures. We observed a maximum value for the MgO buffered sample of about 8.5 × 10−3, and a minimum value of 3.8 × 10−3 for the Cr buffered one.

Ferromagnetic microstructured films of Ni80Fe20 with in-plane uniaxial anisotropy were prepared by RF magnetron sputtering and patterned into rectangles with the larger dimension parallel to the easy axis. Static properties have been measured using a magneto-optic-Kerr-effect test bench, and dynamic properties were also obtained in the microwave frequency range. Because of ferromagnetic resonance, high complex permeability is obtained, and this corresponds to losses that create local heating. So, at an appropriate frequency, a microwave incident magnetic field interacts with the film and generates heating. This heating is recorded using an infrared camera to provide magnetic field pattern images. This setup yields qualitative results and allows for magnetic field detection on a large dimension scale.

We have calculated, by either macrospin analytical method or micromagnetic numerical solving, the microwave assisted switching of a small rectangular platelet as a function of the amplitude and the frequency of a microwave excitation field. The spectral analysis of this phenomenon reveals that microwave-assisted switching is optimal for a rf frequency slightly lower than the linear magnetic resonance frequency measured at low level. Similar experimental results, obtained on 100 μm-scale NiFe structures reveal the same tendency. Switching time for such a process was obtained from calculations that show that sub-nanosecond switching times require combinations of large dc (direct current) and rf (radio frequency) magnetic fields.