Study And Design Of The Detection Electronics Of Magnetic Sensor Based On Fiber Interferometer

Compared with traditional magnetic sensor, fiber-optic magnetic sensor has high sensitivity, large dynamic range, etc., so it has great development potential and application foreground. It becomes the hotspot in the field of research on magnetic sensor technologies. During fiber-optic magnetic sensors, interferometric fiber-optic magnetic sensor using magnetostrictive material has the ability to detect weak magnetic field signals, so it becomes the main direction of the research on weak-signal fiber-optic magnetic sensors. Mach-Zehnder structure and Michelson structure are two typical ones of it.The study target of this thesis is interferometric fiber-optic magnetic sensor. The magnetic sensor based on Mach-Zehnder interferometer has poor stability. The random changes of optical polarization have big affection on it. The traditional Michelson interferometer has been improved by using Faraday reflectors to replace normal ones in it. Thus, the stability problem of the sensor system caused by optical polarization is well solved. The research work of this thesis is mainly focused on the design and implement of detection electronics of the magnetic sensor system based on improved Michelson interferometer. The main productions of the research include:(1) According to the features of the magnetic sensor based on Michelson interferometer, we have studied some key techniques for the detection electronics. We designed and implemented self phase-tracking lock-in amplifier for weak signal detection. It keeps the good detection ability of traditional lock-in amplifier; further more, it makes the phase of reference signal auto-track the input signal, which avoids the errors and troubles by manual tuning.(2) According to the non-linear features of magnetostrictive material, we designed close-loop negative feedback system with fixed bias that keeps the sensor working at its most sensitive situation.(3) We have done a lot of experiments and tests. Through analyzing and debugging of each module of the circuits and the whole system, we have made great improvements on the system's stability and its ability to detect weak signals. Experimental results show that the two techniques referred above make good effects. According to the analysis of the measurement results, the magnetic sensor based on Michelson interferometer, which employing the detection electronics studied and designed in this thesis, has very good performance and high ability of detecting weak magnetic field signals. The weakest magnetic field signal this sensor system can detect reaches 20 nT.Based on these productions, it can be said that the research work of this thesis has acquired good effects and contributed a lot to the research of the whole sensor system.