Research On Temperature Sensitivity Enhancing And Metallized Packaging Of Fiber Bragg Grating

Fiber Bragg Grating(FBG),as an important optical sensor device,is widely used in aerospace,bridge tunnel,petroleum industry and other fields due to its advantages of small size,all-optical transmission,and easy multiplexing.In general,when the FBG is used as a sensor,it needs to be encapsulated to achieve the purpose of protection and sensitization.The common encapsulation method is to use organic glue to bond FBG in the protective shell.However,under special environmental conditions,such as aerospace environment,the FBG sensors encapsulated with organic glue are prone to problems such as creep and aging during long-term use,and are prone to failure in ultra-low temperature environments,affecting the sensing performance.In this thesis,through the combination of theoretical simulation and experimental verification,the simulation and experimental packaging of the scheme of ultrasonic metallizd packaging FBG are carried out,and the temperature sensing performance is tested.The main research contents of this thesis are as follows:(1)The application and research progress of FBG in temperature sensing are introduced.This thesis summarizes the methods of metallized packaging FBG at home and abroad,and analyzes its advantages and disadvantages.The mathematical derivation of FBG coupled mode theory and matrix transfer theory is carried out,and the numerical simulation of FBG is carried out.The reflection spectrum and transmission spectrum of FBG are obtained.The effects of grating length and refractive index modulation depth on reflection spectra are analyzed.Then combined with the FBG sensing mechanism,its temperature sensing model is deduced.(2)Two theoretical models of metallized packaging FBG temperature sensors are established.Combined with mechanical knowledge,the theoretical derivation of the temperature sensitivity of FBG temperature sensors based on embedded and sheet metallized packaging is carried out.The influence of tin-based alloy thickness,package length and substrate material on temperature sensitivity is analyzed,which provides guidance for subsequent design.A scheme based on sheet and embedded ultrasonic metallized packaging FBG is designed,and the combination of COMSOL and MATLAB is used to simulate the temperature sensing performance of the FBG sensor packaged by the two schemes at ultra-low temperature.(3)Ultrasonic metallized packaging based on embedded and sheet is carried out for FBG.Using the packaged FBG sensor to conduct temperature sensing experiments,the results show that the temperature sensitivity of the FBG sensor packaged by the two packaging methods is 3.52 times and 3.73 times that before packaging,respectively,which verifies the theoretical model.The FBG sensor based on the embedded ultrasonic metallized packaging has good wavelength stability.The temperature shock response time of the FBG sensor based on the sheet ultrasonic metallized packaging is about 2.516 s.At the same time,the effects of different metal substrates on the temperature sensitivity of FBG sensors based on embedded ultrasonic metallized packaging are explored.And the effect of different metal substrate thicknesses and different types of metal substrates on the temperature sensitivity of FBG sensors based on the sheet ultrasonic metallized packaging.