Study On The High Temperature Strain Sensor With High Strain Sensitivity Based On FBG

Due to their advantages of high sensitivity and accuracy, immunity to electromagnetic interference and small size, various sensors based on fiber Bragg grating (FBG) are attractive for a wide range of sensing applications, such as petroleum and chemical industry, structural health monitoring, aerospace technique and so on. Monitoring to the strain in high temperature environment are usually used in the petroleum and chemical industry, the traditional electrical sensor can’t be used because of the security problems, but the common fiber Bragg grating strain sensor based on traditional adhesive are unable to achieve measurement requirements for the short life and unstable characteristics. In this thesis, focusing mainly on the high temperature packaging of fiber Bragg grating strain sensor, strain sensitivity enhancement, and high temperature resistant performance after packaging, we mainly complete the following work:1. The high sensitivity fiber Bragg grating strain sensor used in the high temperature environment was designed, fabricated and refined; Considering mainly from the high temperature fiber Bragg grating, fixation and sensing structure, we finalized polyimide-FBG, low temperature glass powder, non-gelling holding fixation methods and rhombus sensing structure.2. Strain transfer theory of the rhombus sensing structure were analyzed and the relationship between real strain and Bragg wavelength is determined; we also analysis the drift of Bragg wavelength and strain measurement range.3. ANSYS finite element analysis software were chosen to simulate strain transfer process for the above rhombus structure and two lever strain sensitizer structure, and stress distribution under the effect of external stress load were obtained.4. Finally, the characteristics of time, strain and temperature for the above sensing rhombus structure was tested. In the time characteristic, Bragg wavelength presented a kind appearance of "rectangle wave", which indicated an excellent grip effect;Bragg wavelength emerged a "flat stage" due to the limit normal prestress when the strain goes to a certain extent which consistent with the expected effect; the compress strain characteristic presented a good linearity unless it is broken, and the strain sensor can still work at 300℃; the experimental results show the average strain sensitivity of compress and tension is 11pm/με and 12pm/με, respectively.Two excellent fixations-permanent and active connections were achieved, which indicate entirely different performance, high train sensitivity and tunable prestress.