Research On Optical Fiber Vector Magnetic Field Sensing Technology Based On Magnetic Fluid

Today,with the highly developed technology,electromagnetic field sensing technology has become an indispensable part of the modern information industry.Especially in the field of geomagnetic navigation and satellite space exploration,high sensitivity vector magnetic field sensors are needed to measure the geomagnetic field and spatial magnetic field distribution.Compared with the traditional magnetic field sensing technology,the optical fiber magnetic field sensing technology has the advantages of small size,light weight,anti-electromagnetic interference and high sensitivity,which further improves the performance of the magnetic field sensor.Moreover,as an excellent magneto-optical material,magnetic fluid has many unique optical characteristics,such as tuned refractive index characteristics,birefringence effect,thermal lens effect,and magneto-electric direction effect.The combination of magnetic fluid as magneto-optical material and optical fiber sensing to measure magnetic field can realize the perception of vector magnetic field and has the advantage of high sensitivity.Therefore,magnetic fiber-based fiber-optic vector magnetic field sensor is becoming a hot spot for many people.Aiming at the problems of vector magnetic field measurement and fiber-optic sensing structure and the research of fiber-optic vector magnetic field sensing technology,this paper proposes a magnetic fluid-based fiber Fabry-Perot(F-P)vector magnetic field sensor.In this paper,the magneto-optical characteristics of magnetic fluid and the principle and fabrication method of optical fiber F-P interferometer are studied.The vector magnetic field characteristics of the fiber-optic F-P vector magnetic field sensor filled with magnetic fluid are also studied.The main research results of this paper are as follows:(1)The microstructure characteristics of magnetic particles in magnetic fluid and the longchain model under external magnetic field are studied.The model explains the relationship between the refractive index of magnetic fluid and the applied vector magnetic field.Theoretical analysis of fiber F-P interferometer is carried out,and F-P structure is optimized by lens fiber.Theoretical analysis,simulation calculation and experimental verification of this new structure using Gaussian beam theory.This model can be used to optimize lens fiber parameters to achieve high quality spectra at any cavity length.(2).According to the characteristics of the studied magnetic fluid and the sensing principle of the F-P interferometer,the structural parameters and performance of the F-P interferometer used were analyzed.The fabrication process of three fiber F-P interferometers was explored,and the temperature performance of the interferometer was tested.The best air cavity F-P interferometer has a temperature sensitivity of 4.7 pm/℃.The magnetic fluid filling technology of three kinds of FP interferometers was explored,and the magnetic fluid-based fiber FP vector magnetic field sensor was finally fabricated.After filling,the magnetic field sensor was tested for temperature and magnetic field performance.The temperature sensitivity of the sensor was-66.4 pm/℃.and the magnetic field sensitivity was 191.2 pm/Gs.(3)A three-dimensional magnetic field generating device is designed and built,and an automatic data acquisition and processing program for experimental data is written.Then,the vector magnetic field characteristic experiment of the magnetic fluid-based fiber F-P vector magnetic field sensor was carried out,and the refractive index of the magnetic fluid was obtained under different magnetic field directions and magnetic field strength.The vector magnetic field measurement is realized by analyzing the vector magnetic field characteristics of the magnetic fluid by combining theory.