Optic Fiber Magnetic Field Sensor Based On Refractive Index Regulation And Magnetostrictive Effect

As a basic physical quantity,the magnetic field is closely related to human life which has both intensity and direction.At present,magnetic field sensors for detecting magnetic fields have been widely used in industry,military and biomedicine.Most of the traditional magnetic field sensors are electrical sensors,which mainly have disadvantages such as large space occupation,high cost,and anti-electromagnetic interference.The optical fiber magnetic field sensor has become a key part of the next generation all-optical sensor network,with high integration and sensitivity.It is easy to integrate and reuse in the existing alloptical sensor network to achieve higher efficiency and high-speed network magnetic field monitoring.Based on this,this thesis designs a refractive index-regulation fiber magnetic field sensor based on the optical microfiber coupler interferometer(OMCI),and conducts research about optical fiber magnetic field sensor based on fiber Bragg grating(FBG)and magnetostrictive effect for the application requirements of magnetic field sensing,the main research contents are as follows:(1)Firstly,the research progress of optical fiber magnetic field sensing technology is reviewed,and the advantages and disadvantages of electrical magnetic field sensors and optical fiber magnetic field sensors are compared.The advantages and disadvantages of optical fiber sensing structures such as Faraday optical effect type,Ampere force optoelectronic hybrid type,atomic spin optical pump type,refractive index-regulation type,magnetostrictive integrated type,etc.are summarized and compared,and the application prospect of these optical fiber magnetic field sensors is analyzed.(2)A structure of a reflective index-regulation optical fiber magnetic field sensor based on OMCI and magnetic fluid is proposed.Through the optical field transmission mechanism of fiber coupling and the refractive index control theory of optical microfiber coupler,the theoretical formula of the output of the sensor is deduced,and the control relationship between the transmission spectrum of OMCI and its structural parameters is simulated and analyzed by numerical analysis and calculation method.The magnetic field response and temperature response of the proposed refractive index-regulation optical fiber magnetic field sensor are simulated and compared.The simulation results show that the interference characteristic peak of the output spectrum is red-shifted with the increase of the magnetic field,and blue-shifted with the increase of the temperature.The simulation results provide the design basis and theoretical basis for this type of fiber optic magnetic field sensor.(3)The proposed refractive index-regulation optical fiber magnetic field sensor based on OMCI is designed experimentally,and the sensor is encapsulated by the optical microfiber coupler(OMC)and magnetic fluid(MF)using polydimethylsiloxane(PDMS).In addition,the sensor samples under different OMCI structural parameters are tested and verified for their performance.The experimental results are consistent with the simulation,and the magnetic field sensitivity of 96.8pm/Oe and the temperature sensitivity of-919.1pm/℃ are respectively achieved.The magnetic field vector sensing with a period of 180° is realized in the X-Z two-dimensional plane,and the measured response time is998 ms.Meanwhile,the magnetic field detection ability is 0.101Oe(10.1μT),which can meet the international geomagnetic standard(10μT ～ 100 u T).Besides,the magnetic field and temperature response results of the sensor are analyzed by the method of sensitivity matrix demodulation.The demodulation results show that the sensor not only does not need temperature compensation,but can also accurately demodulate temperature.It solves the long-standing temperaturesensitive crossover problem of fiber-optic magnetic field sensors in engineering.(4)A magnetostrictive optical fiber sensor based on FBG is studied,and the magneto-temperature response characteristics of this type of sensor are verified by simulation and experiment.A magnetostrictive effect optical fiber sensor based on FBG is studied,and the sensing mechanism based on magnetostrictive effect and the method of magnetic field and temperature dual-parameter demodulation based on FBG cascaded array are analyzed.The magnetic field and temperature response characteristics of this sensor are verified by simulation and experiment.The experimental data results show that the magnetic field sensitivity and temperature sensitivity of the sensor is 0.21 pm/Oe and-10.2 pm/℃,respectively.At the same time,the sensor realizes magnetic field vector sensing with a period of 180° on the X-Z and Y-Z planes,while the period on the X-Y plane is 0.The experimental results provide an alternative solution for the future integration of two-dimensional probes to fabricate three-dimensional vector magnetic field sensors.The optical fiber magnetic field sensors studied in this paper have the advantages of high sensitivity,simple fabrication,low cost,and high integration.They have important application potential in scenarios such as wearable security environment monitoring and marine magnetic field network detection.