| High temperature sensing has always been an important research direction for researchers in various countries.The applications include in this prospective are aerospace,petrochemical,and marine industries,and is a cutting-edge technology related to the state's advanced equipment manufacturing.Due to the complex and rigorous application environment,high-temperature sensors not only require sensor materials to measure high temperatures,but also ensure the stability and accuracy for the smooth operation of employed sensors at high temperature environments for long term deployment basis.Fiber optic sensors having rate of versatility to focus research area which includes intrinsic safety,small size,high sensing accuracy,antielectromagnetic interference,easy to connect network and high temperature resistance of materials.Besides multi-parameter,high-sensitivity measurements are also an important trend in the development of fiber optic high temperature sensing technology.Based on the above background,the FBG/EFPI temperature and pressure sensor was prepared with the help of femtosecond laser micromachining technology.The develop sensor having ability to measure the temperature and pressure in the complex environment,simultaneously.Finally,the Vernier effect was applied to the fiber FPI,which can simply and efficiently improve the air pressure sensitivity of sensor and achieve high sensitivity sensing.The main contents of the working is summarized as:(1)The development status of fiber-optic FPI strain sensor,fiber FPI air pressure sensor and FBG/EFPI multiplex sensor at home and abroad are investigated,the Vernier effect are introduced.Finally,we summarized and analyzed the research output with comparison of earlier work in the field Optic Fiber Sensing and further,determine the research direction in subject topic.(2)In order to solve the problem that the grating in conventional FBG/EFPI composite sensor is erased easily at high temperature,high-temperature annealing method is adopted to produce high-reflection regenerative FBG on hydrogen-carrying fiber.For stability of wavelength of regenerated FBG,the study outcome after repeated heat treatment at a maximum of 800 ?,the error of the grating wavelength at the same temperature is only about 5 pm.(3)The regenerated FBG was applied to the FBG/EFPI composite sensor,and then the sensor was placed on the surface material No.45 steel by stepwise model for high temperature sensing.On the other hand a large aircraft model gave instantaneous heating response while experiments to study the high temperature resistance of the sensor.In these two experiments,the sensor rapidly reacted with accuracy,and there was no resultant error in light intensity attenuation,material deformation at the high temperature.(4)Based on the high temperature performance of the FBG/EFPI composite sensor,using femtosecond laser micromachining technology,a square open cavity for gas inlet and outlet was proposed on the side of the capillary glass tube with integration of FBG/EFPI temperature and pressure sensor.The pressure sensitivity of the sensor at normal temperature,100 ?,150 ?,and 200 ? was studied,which were 4.11,3.21,2.79 and 2.18 nm/MPa,respectively.In parallel,FBG measured the high temperature 108.8 ?,160.3 ?,and 213.6 ?,respectively.The grating was used in cascade formation to measure temperature,also can realize temperature compensation of the sensor and eliminate temperature cross sensitivity to improve sensing accuracy.(5)A high-sensitivity fiber EFPI air pressure sensor was proposed which can adjust the position of the employed fiber to generate Vernier effect.The sensor with Vernier effect can solve the problem of low sensitivity of ordinary open-cavity pressure sensor.The sensor which has the largest envelope period was tested at the 0.16 and 0.6MPa.Subsequently,the sensitivity of the sensor was recorded 86.58 and 86.64 nm/MPa,respectively.The sensitivity amplification factor was 32.8,which can achieve high sensitivity sensing. |
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