Research On Vibration Sensing Of Fiber Grating

In recent years,with the rapid growth of the world's energy consumption demand and the increasingly prominent contradiction between supply and demand,the importance of oil and gas exploration has gradually emerged.Seismic exploration technology is the most widely used in oil and gas exploration activities and is widely used in the process of oil exploration and development.The advantages of Fiber Bragg grating(FBG),such as small size,anti-electromagnetic interference,and lightweight,make FBG vibration sensors gradually reveal their application value in seismic exploration.In this paper,the FBG vibration sensor is mainly studied with FBG as the sensing element.The main work of this paper is as follows:(1)The oil and gas seismic exploration and common geophone types are introduced,the working principles of several optical fiber vibration sensors are briefly described,and the research status of Fiber Bragg Grating vibration sensors is summarized.Based on FBG coupled-mode theory,the corresponding principle is analyzed theoretically.Based on the general mechanical model of the vibration sensor,the mechanical model of the FBG vibration sensor is constructed.(2)A double FBG vibration sensor based on 'E' beam is proposed.The working principle of the proposed FBG vibration sensor structure is analyzed and theoretically deduced,and the relationship between the length of the cantilever beam and the effective length of the fiber grating in the structure and the natural frequency and sensitivity is simulated.Finally,the first four vibration modes are analyzed through finite element analysis,which provides a solid foundation for the experiment.The experimental results show that the natural frequency of the sensor is 83 Hz,the amplitude of FBG center wavelength is relatively flat in the range of15-60 Hz,and the sensitivity is up to 240.67 pm/g,and the linear fitting degree is up to99.96%.(3)A two-dimensional cantilever vibration sensor based on the cantilever beam FBG is studied.After theoretical analysis and the related formula are derived,respectively from the beam length,fiber length and the inertial mass effectively block as a starting point,to establish the relationships between each natural frequency and sensitivity of the simulation model,through the finite element simulation,observe the sensor structure in the first four order natural frequency of the modal strain,finally verified experiment.The experimental results show that the natural frequencies of the vibration of the sensor in the x/y direction are 505Hz/177 Hz respectively.And the flat region of the sensor response in the x and y directions is60?150Hz and 30?150 Hz,respectively.The sensitivity of the sensor in the x and y direction of vibration is 125.85 pm/g and 82.32 pm/g,respectively.(4)A beam-based FBG temperature compensation vibration sensor is designed.The structural parameters of the sensor are determined by theoretical analysis and finite element simulation.The experimental results show that the sensor has a good response flat region in the range of 40?140Hz.The sensor has a natural frequency of 247 Hz,a sensitivity of 234.5pm /g,and a linearity of 99.9%.In the range of 25?75 ?,the influence of sensor structure on temperature is reduced to 0.47 pm/?.The dynamic range of the proposed FBG vibration sensor is 62 d B.