Study On The Technology Of Weak Magnetic Field Measuring Sensor Based On Optic-Magnetism

This thesis mainly studies on the technology of magnetic field measuring sensors based on the giant magnetostriction(GMS), attempting to increase the sensitivity of the magnetic field measuring sensors, decrease the volume of the transducer and improve the stability of the entire system.The Livingston Correlative Rotation Model (LCRM) has been educed theoretically according to the principle of the magnetization MS rotation. The conclusion that the magnetostriction of the materials depends on the part of the external magnetic field which is parallel to the measured direction of the strain and vertical to the direction of the easy magnetization has been given, after analyzing the relation between the direction of the external magnetic field and the magnetostrictive strain. On condition that magnetization of the materials is unsaturated, the two primary factors causing hysteresis are the pinning effect of the impurity and stress in the materials and magnetization irreverse rotation. The formula of the domain wall displacement versus magnetostriction has been given, which shows obviously that hysteresis influenced magnetostriction.The performances of the four traditional coupled structures of the giant magnetostrictive materials (GMM) and the optic-fiber have been analyzed, and the advantages and disadvantages of them are pointed out. The GMM/optic-fiber plating film structure is got from improving the coated structure. The new structure has high transduction coefficient, small load effect and good flexibility. Load characteristics and the relation between strain and phase change are also analyzed. Based on these analysises, it has been proved that the transducer with racetrack structure has better phase output and orientation. We are trying to make the new structure by metal vapor deposition, searching for the adequate technics parameters,and test the performance of the TbDyFe film with a cantilever beam.Through analyzing the characteristics of the various interferometers, we deem that the Mach-Zenhder interferometer is more adequate to measure the strain of the giant magnetostrictive transducer in the external magnetic field. Then we introduce the struct- ure of the Mach-Zenhder interferometer in the measuring loop of the entire sensor and the PI control method for phase orthogonality. We improved the former algorithm with digital method after analyzing the phase demodulation algorithms of the Mach-Zenhder interferometer, and tested the improved algorithm in the measuring system setted up by ourself.The phase generated carrier demodulation algorithm and 3×3 coupler demodulate- on algorithm have been introduced, then it has been pointed out that 3×3 coupler demodulation algorithm has simple structure, convenient calculation and higher precision. We set up a Mach-Zenhder interferometer, and verified the feasibility of the magnetic field measuring scheme.