Research Of Fiber Bragg Grating Magnetic Sensor Based On Magnetostrictive Materials

In engineering applications,the measurement of magnetic fields in the electrically insulated working environment and the measurement of weak magnetic field signals are gradually increasing.The use of optical fiber as the transmission medium,has significant advantages such as anti-electromagnetic interference and high resolution.The fiber grating magnetic field sensor based on the giant magnetostrictive material can be well applied in the magnetic flux leakage and weak magnetic environment.The sensing principle of this magnetic field sensor is the combination of the magnetostrictive material and the fiber grating,The magnetic field is measured by the change of the strain of the magnetostrictive material caused by the magnetic field.In this paper,the optic-fiber magnetic field sensor is designed.The giant magnetostrictive material is combined with the fiber grating sensor.The magnetic induction intensity is measured by monitoring the wavelength deviation of the fiber.The transfer principle of the grating strain and the magnetostrictive effect were analyzed.The magnetostrictive coefficient of the giant magnetostrictive material was measured under the pulsed magnetic field.The magnetostrictive linear range was found for practical measurement.The sensing probe and the energized coil used as magnetic field generator were designed.The sensor system implements a double-grating temperature compensation scheme to eliminate the effect of the temperature on the wavelength variation of the optical fiber,and ultimately the corresponding magnetic field strength caused only by the magnetostriction was obtained.In the thesis,the development of magnetic field measurement technology and several different magnetic field measurement principles are introduced.Different types of optical fiber sensors currently used in magnetic field measurement fields are compared,and the research status of optical fiber magnetic field sensors at home and abroad are discussed.The theoretical analysis of the sensing principle of the optical fiber sensor is conducted.The effects of the axial strain and the temperature change on the wavelength are discussed.The force analysis was performed on the middle adhesive layer of the grating.The influence of various sticking factors on the transmission efficiency is considered.And the relationship between the wavelength variation of the grating and the magnetic field intensity is deduced.The experimental preparation for the optical fiber sensor is prepared,A practical structure of the sensor probe and a feasible paste method for the fiber are designed;The structure of electric coil is modelled with the COMSOL Multiphysics software.Different methods of measuring the magnetostriction coefficient is introduced;An experimental method worked in the pulsed magnetic field is proposed.The basic idea is to ensure that the detection coil and the fiber grating perform simultaneous measurements under the same magnetic field conditions.The induced electromotive force was measured by the detection coil,then the magnetic induction intensity was integrated.The magnetostrictive deformation was measured by the fiber grating to obtain a magnetostrictive coefficient corresponding to the magnetic induction intensity.A double-grating temperature compensation scheme is designed for the linear region of magnetostriction.A temperature-compensated grating is placed next to the magnetic field measurement grating,and the wavelength change of the two gratings at different magnetic field strengths is acquired.Mathematical operations are performed to eliminate the temperature errors,and the linear relatiosnship between the wavelength variation and the magnetic field intensity is obtained.