Improvement And Design Magnetic Field Sensing Scheme Based On MF And LPFG

Long period fiber grating (LPFG) is a new kind of passive optical device which is more sensitive to the factors of temperature, strain, ambient refractive etc.. Magnetic fluid is a kind of special liquid which has obvious magnetic optical effect, for the refractive index changes with the external magnetic field, it is often used in magnetic field sensing. The refractive index sensitivity of LPFG is combined with the magneto optic effect of MF, and the resonance wavelength shift of LPFG can be used to measure the magnetic field.This magnetic field sensing system not only has the advantages of high sensitivity of LPFG, but also has the advantages of high conversion efficiency of MF, which has a certain significance to the practical application.This paper expounded the sensing principle of long period fiber gratings, described the composition, properties, applications of magnetic fluid in detail, the key to carry out simulation research on temperature characteristics of LPFG magnetic field sensor based on the magnetic fluid, the simulation results show that the change of ambient temperature will cause the resonant wavelength of the LPFG coupling shift, while changing the refractive index of the magnetic fluids, influence the effects of magnetic field measurement precision, so it need to add a temperature improvement module. By analyzing the principle of the improved module,get the conclusion that the magnetic field intensity can be obtained accurately by measuring the refractive index and temperature of the that.Aimed at the need that Prague optical fiber grating (FBG) has the advantages of wide range of temperature and the need for the improvement of the program,study the relationship between of cladding thickness and temperature and refractive index is studied.The results show that the thickness of the cladding layer will not affect the temperature sensitivity of FBG, but it will affect the sensitivity of refractive index, the thinner the cladding thickness, the higher the refractive index sensitivity; Propose the two improved schemes through the analysis of the improved module and results of FBG clad thicknessThe first method is to improve the method of simultaneous measurement of temperature and refractive index by adding a thin layer of FBG.Through analysis and numerical fitting of refractive index sensitivity interval extract the formula that can simultaneous measurement of temperature and refractive index.Furthermore,the correctness of the formula is verified by the 3D simulation of MF,proved that the improved method can improve the measuring accuracy of the magnetic field. And when the refractive index is between 1.45-1467, the magnetic field measurement accuracy of the proposed scheme will reach the highest.At last, the improved system model is made by designing a new type of sensor probe.The second is to add FBG, the formation of temperature compensation module method to improve.At first, through the comparison of the temperature and the medium, the FBG with wide temperature range is selected as the temperature compensating medium.Then for the defect of FBG temperature insensitive, the method of boron andGermanium Co doped, point by point writing method and the method of FBG is used to improve the temperature sensitivity of the system.At last, through the modeling and analysis of the improved scheme, this method can also be concluded that the temperature compensation method can measure the magnetic field, and the purpose of improving the accuracy of the magnetic field measurement is realized.