Fiber-optic Magnetic Field Sensor Transducer And System Research

. In the thesis, we described a polarization-insensitive fiber optic Michelson interferometric weak magnetic field sensor. The fiber optic magnetostrictive transducer and structure of the sensor are analyzed and discussed. A weak magnetic field sensor is set up and the experimental result are obtained. The operating principle, the designing and fabricating method of optic fiber magnetostrictive transducer are introduced in the thesis. By the methods of increasing sensing fiber length and using silica fibers with 80-μm-diameter, dual-strip fiber optic magnetostrictive transducers with high magnetic sensitivity were made. And it was applied in the fiber optic Michelson interferometer. In addition, the factors which affect the transducer operating are analyzed and the corresponding improvement methods are also presented. To the sensor system, the problem of the signal fading caused by polarization fluctuation and random phase shift is presented. Jones matrix method is used to analyze the principle eliminating polarization-induced fading in Michelson fiber interferometer, which method need no extra signal processing while just by inserting Faraday Rotator Mirror (FRM) into the fiber interferometer. Finally, a weak magnetic field fiber optical sensor is set up. By active scanning method, the output signal of the sensor is detected and analyzed under different AC modulating magnetic fields. The experimental results indicate that output signal is linear with the detected magnetic field, which accord with the theoretic analysis. The phase sensitivity of the sensor is 2.8 ×10 ?5rad /nT, and minimum detectable magnetic field is 600nT.