Study On PCF-SPR Sensing Characteristics And Application In Magnetic Flux Leakage Detection For Pipeline Defects

As an important branch of Non-destructive Test(NDT),magnetic flux leakage(MFL)detection has become the main way to detect pipeline defects due to its advantages of simple structure,easy operation and automation.Conventional MFL sensing components have the advantage of fast response speed,but in practical detection applications,there are problems such as insufficient sensitivity,poor reliability and electromagnetic interference resistance,easy to create secondary interference,and limited detection range.Compared with the traditional electric signal magnetic field sensing device,optical fiber sensing based on optical technology has many unique advantages in the field of magnetic field,such as strong anti-interference,insulation corrosion resistance,small volume and weight,reusability and traceless online detection.Meanwhile,due to the two-dimensional flexible structure design of Photonic Crystal Fiber(PCF),combined with the Surface Plasmon Resonance(SPR)effect.It provides a feasible way to realize the sensor design with good reliability,high sensitivity,easy integration and multi-function.According to the tunable refractive index Magnetic field of Magnetic Fluids(MFs),in order to realize the simultaneous detection of Magnetic field and temperature as well as temperature compensation,two PCF-SPR sensing models were designed in this paper.The main research contents of this paper are as follows:(1)In order to realize the multi-parameter refractive index guided sensor detection.Ag-Si₃N₄ composite film was introduced as the sensitive layer of SPR excitation,and a dual-channel simultaneous detection PCF-SPR sensor model was proposed,and its specific finite element numerical study was carried out.Firstly,the model structure is constructed,the material properties are studied,and the coupling electric field mode is analyzed and selected.Secondly,in order to study the dependence of the sensor coupling characteristics of the model on the geometric structure parameters,the effects of different structural parameters on the fundamental mode limiting loss spectra were discussed.Finally,according to the wavelength inquiry mechanism,the feasibility of dual-channel simultaneous refractive index detection is proved,and the average and maximum sensitivities of the two channels in the refractive index detection range are obtained after the structure optimization.The sensor model provides the basis and theoretical basis for the magnetic field and temperature refractive index guided double parameter detection in the next chapter.(2)In order to intuitively understand and analyze the magnetic flux leakage characteristics of pipeline defects,COMSOL software was used for 3D modeling and simulation,thus leading to the selection of MFs as the magnetic and photosensitive functional material.In addition,in order to realize the simultaneous detection of temperature and temperature compensation of magnetic fluid,a dual-channel refractive index guided PCF-SPR sensor is introduced to simultaneously detect magnetic field(H₀)and temperature(T).According to the magnetic field intensity of the defect MFL and the detection range of the two-channel sensor,the water-based MFs with the particle volume concentration of 1.8%was finally selected as the magneto-photosensitive material,and the influence of temperature on the sensor was discussed.The magnetic field sensitivity and temperature sensitivity of the sensor were obtained by analyzing the sensor characteristics and demodulation of the transfer matrix model.(3)In order to improve the detection accuracy of measured parameters,a PCF-SPR sensor with double grooving on the side is proposed to realize dual-channel sensing by adjusting the incident polarization mode of light.The FEM numerical simulation of the sensor is carried out,the coupling characteristics between the modes are analyzed,and the dependence of the fundamental mode limiting loss spectrum on different structural parameters is discussed.It is proved that the sensor can effectively overcome the problem of multi-parameter cross sensitivity.After the structural parameters are optimized,the magnetic field sensitivity and temperature sensitivity of the sensor are obtained through the analysis of the sensor characteristics and the demodulation of the transfer matrix model.The sensor model not only has excellent detection sensitivity and accuracy,but also is easy to realize real point detection by miniaturization.