ETUDE ET MISE EN OEUVRE DE MAGNETORESISTANCES ANISOTROPES ET A EFFET TUNNEL POUR LA MESURE DES CHAMPS MAGNETIQUES FAIBLES DANS LES PLASMAS SPATIAUX

摘要

In situ study of Sun-Earth relations and ionized environments of our solar system needs for the measurement of waves propagated in magnetized plasma. Aboard space observatories, wave's magnetic components are measured by inductive magnetometers. High frequencies measurement (a few Hz up to a few 100 kHz) is made by Searchcoil magnetometers whereas low frequencies (a few Hz down to a few 10 mHz) and dc field measurement are leaved to Fluxgate magnetometers. In this thesis we deal with the design of a broadband magnetometer able to measure magnetic fields from dc to a few kiloHertz. We present an innovative instrumental concept based on the implementation, in a unique instrument, of both an inductive and a magnetoresistive measurement of the magnetic field. We address both the design and the study of anisotropic (AMR) and tunneling (TMR) magnetoresistive sensors whose magnetic properties are controlled by exchange anisotropy. We show how those sensors can be associated to a Searchcoil magnetometer whose ferromagnetic rode is used to achieve an efficient magnetic concentrator. We then detail the design of a hybrid Searchcoil/Magnetoresistor magnetometer meeting the environmental constraints associated to space experiments as well as an original optimization tool based on finite element modeling and a genetic algorithm. We finally prove the feasibility of the concept making a fist prototype of a hybrid tri-axes Searchcoil/PHE sensor magnetometer and its low noise conditioning electronics. This prototype reaching a detectivity around 200 fT/sqrt (Hz) at 1 kHz and 400 pT/sqrt (Hz) at 1 Hz has been tested in real conditions during a scientific rocket experiment.