Gérard Chanteur

Numerical simulation of the MHD equations by a kinetic-type method

We introduce a flux-splitting formula for the approximation of the ideal MHD equations in conservative form. The Faraday equation is considered as the average of an abstract kinetic equation, giving a flux-splitting formula. For the other part of the equations, we generalize formally the classical half-Maxwellian flux-splitting of the Euler equations. Numerical results on MHD shock tube problems are displayed.

Principle and Performance of a Dual-Band Search Coil Magnetometer: A New Instrument to Investigate Fluctuating Magnetic Fields in Space

Search-coil magnetometers are of common use in space physics thanks to their simplicity, robustness and ability to measure weak magnetic fields: their sensitivity can reach a few tens of fT/¿Hz in the range 10-100 kHz. The frequency band is grossly determined by the resonance of the coil. Simply adding a second coil does not efficiently extend the frequency band beyond the first resonance due to the mutual impedance of the two coils. We present a solution, called ¿mutual reducer,¿ which allows us to take full benefit of the second coil and efficiently extends the frequency band. The physical principle is described first, followed by a detailed presentation of this ¿dual-band search-coil¿ (DBSC) that will be part of the plasma wave instrument (PWI) onboard the Mercury magnetospheric orbiter (MMO) of the ESA-JAXA mission BepiColombo dedicated to the exploration of the plasma environment of planet Mercury.

High magnetic field amplification for improving the sensitivity of Hall sensors

This paper describes the design of two magnetic concentrators that can be used to intensify the magnetic field in the active region of magnetic sensors, such as Hall sensors. The literature provides many examples of magnetic amplification, but magnetic gains never exceed 100 typically (Drljaca et al. 2001, Drljaca et al. 2002). We demonstrate that a larger magnetic field amplification (~1000 and even higher) can be achieved. Magnetic field amplification can even exceed the theoretical value fixed by the relative permeability of the material. Thus, the effective sensitivity of Hall sensors can be improved by at least three orders of magnitude by implementing them inside an especially tailored magnetic concentrator; noise-equivalent magnetic induction spectral density (National Electronics Manufacturing Initiative spectral density) down to 10 pT/radic(Hz) should be reached, using a good conditioning electronic

Feasibility of a Giant MagnetoImpedance Sandwich magnetometer for space applications

Space experiments require very efficient magnetic field sensors. Until now, fluxgate remains the most competitive way to measure weak magnetic field in space in spite of some drawbacks, like their offset drift. Since few years, giant magneto-impedance (GMI) effect were intensively studied and have shown promising results. Thus, we present a new GMI sandwich magnetometer for space application. The GMI sandwich transducer was fabricated with nanocrystalline alloy films and copper film. Very low noise amplifier is combined with an AM demodulation to extract weak dc-low frequency magnetic field from carrier. Noise equivalent magnetic induction (NEMI) is improved thanks to an experimental optimization method enables to increase the intrinsic sensitivity and use of a ratio transformer optimization to reduce noise electronic. We have obtained a flat transfer function in the frequency range [DC-1 kHz]. In this broad range, sensitivity is equal to 1000 V/T and NEMI reaches few nT/sqrt(Hz).

Design of magnetic concentrators for high sensitivity anisotropic magnetoresistor devices

In this work, a very promising shape of magnetic concentrators taking advantage of the symmetrical flux leakage of Mn–Zn ferrite magnetic cores is presented. This configuration consists of two ferromagnetic rods separated by two air gaps allowing to place anisotropic magnetoresistance sensors in the core axis. Results from three-dimensional finite elements modeling are presented. We show that an appropriate shape optimization of core extremities enables to improve significantly the amplification factor without any increase in length.

Optimization of the Shape of Magnetic Field Concentrators to Improve the Sensitivity of Hall Sensors (Optimierung von Konzentratoren für magnetische Felder für die Steigerung der Empfindlichkeit bei Hallsensoren)

Summary This paper describes the design of a set of two magnetic concentrators which can be used to intensify the magnetic field in the active region of magnetic sensors, such as Hall sensors. Literature provides many examples of magnetic amplification, but magnetic gains never exceed 100 typically [1, 2]. We demonstrate that larger magnetic field amplification (∼1000 and even higher) can be achieved by implementing an appropriate geometry. Magnetic field amplification can even exceed the theoretical value fixed by the relative permeability of the material. Thus the effective sensitivity of Hall sensors can be improved by at least three orders of magnitude by implementing them inside especially tailored magnetic concentrators; noise-equivalent magnetic induction spectral density (NEMI spectral density) down to 10 pT/√Hz should be reached, using a good conditioning electronics. We present a formulation of our design process as an optimization problem and use it to find an optimum shape for the magnetic concentrators in a simple case.