Research On The Properties Of Optical Fiber Vector Magnetic Field Sensor Based On Magnetic Fluid

In recent years,magnetic field measurement technology has developed rapidly.However,at present,most measurement methods only consider the magnetic field strength,and ignore the measurement of vector magnetic field.Therefore,research on vector magnetic field sensing is very necessary.Optical fiber has many advantages such as electrical insulation,corrosion resistance,small size and light weigh.As a new kind of functional material,magnetic fluid(MF)has properties of fluidity of liquid and magnetic properties of solid magnetic particles,it presents unique magneto-optical properties,including tunable refractive index,Faraday rotation,thermal lens,dichroism and birefringence effects.In this paper,in order to solve the problem of vector magnetic field measurement,the optical fiber and magnetic fluid are combined to research on the properties of optical fiber vector magnetic field sensor.The proposed sensor has many advantages such as high sensitivity,high reliability,anti-electromagnetic interference and remote sensing.This paper researched the properties of optical fiber vector magnetic field sensor based on magnetic fluid,the research work and achievements include the following components:(1)According to the anisotropic distribution property of magnetic nanoparticles on the surface of the fiber under the action of magnetic field,SM-MM-SM fiber and core-offset structure has been proposed and the the principle of vector magnetic field sensing is explained.The structure of different parameters has been simulated by Rsoft and sensing length and core offset have been determined.(2)According to the simulation results,the fabrication method of SM-MM-SM fiber and core-offset structure is performed,and the performance of the sensing structure has been tested.After the fabrication of magnetic field sensor,the experiment system of the magnetic field sensing has been set up and magnetic field measurement experiment has been performed.According to the experimental results,the deficiencies of the sensor have been analyzed.(3)Three methods have been proposed to improve sensing performance of the sensor.By comparing these methods,the best one has been selected and SM-MM-TC fiber and core-offset structure has been proposed.Through simulation analysis,multimode fiber length S,core offset D and sensing length L of the sensing structure have been determined.(4)The fabrication method of magnetic field sensor based on magnetic fluid and SM-MM-TC fiber and core-offset structure has been studied.In order to realize the experimental measurement of vector magnetic field,a direction-controlled uniform magnetic field equipment has been designed and a vector magnetic field experimental system has been established.The magnetic field direction response and magnetic field strength response of the sensor have been measured.According to experimental results,the properties of optical fiber vector magnetic field sensor have been analyzed.The results show that the proposed sensor is sensitive to changes of magnetic field direction and magnetic field strength,the magnetic field sensitivity of proposed sensor can be up to 112.95 pm/Gs.In the vector magnetic field measurement,the magnetic field sensor can be axially rotated to determine the direction of the magnetic field,and the magnetic field strength can be calculated by the value of wavelength shift,thereby realizing the measurement of the vector magnetic field.Experiment system of temperature response has been established to study the influence of temperature on the sensor.