| Optical Fiber Bragg Grating(Fiber Bragg Grating,FBG)sensing technology not only has the characterisstics of small size,light weight and strong anti-electromagnetic interference ability of optical Fiber sensor,but also has advantages of low demodulation cost and high sensitivity,so it is widely used in aerospace and Marine equipment,geotechnical slope monitoring and structural health monitoring.At present,in slope monitoring,although commercial high-precision electrical sensors can meet the needs of slope prevention,they are still vulnerable to the influence of complex environment.The slope displacement sensor based on FBG needs to consider temperature-stress cross-sensitivity,device packaging and serial point layout.Therefore,this paper will focus on the design,preparation and performance of FBG displacement sensing system with high sensitivity and low cost and the application of slope.The main work is as follows:(1)Based on the selection of phase mask period before writing FBG by phase mask method,the SIMULATION experiment of FBG model and its stress and temperature sensor is carried out.The experimental results show that the phase mask with a period of 1056.5 nm corresponds to the FBG with a central wavelength of 1550 nm.The simulated stress sensitivity is 0.92 pm/με,and the temperature sensitivity is 13.75 pm/℃,which provides theoretical basis and experimental data reference for the subsequent design of FBG displacement sensor.(2)Aiming at the crosstalk problem caused by 3 d B bandwidth at the center wavelength of series FBG,the effects of four writing parameters,including laser output energy,gate length,mask and fiber distance,and fiber axial tension,on FBG performance were studied;The total output energy of the laser is 0.6 k J and the length of the grid area is 10 mm as the optimal writing parameters of FBG.Two writing parameters,namely the mask and the fiber distance and the axial tension on the fiber,are used to write multiple central wavelengths on a mask.(3)The advantages and disadvantages of reference grating method and dual grating differential output method are compared for FBG stress-temperature cross sensitivity problem.The influence of different substrates on the temperature performance of FBG was studied,and the FBG displacement sensor was fabricated based on quartz glass substrate.The displacement test platform and water bath equipment were used to verify the displacement and temperature performance of the sensor.The results show that the displacement sensitivity of the sensor is 145.08 pm/mm,the temperature sensitivity is 9.22 pm/℃,the accuracy is 1.43%,the error is 1.55%,the static comprehensive relative error is 2.88%,and the measuring range is 10 mm.(4)According to the application of the monitoring system in the actual scene,a five-point quasidistributed FBG displacement sensing monitoring system is prepared,and the monitoring system is used to measure temperature compensation performance and study the scenario application of abnormal soil compression deformation,fracture development process of soil deformation and cutting slope of soil slope deformation under actual scene.The results show that the change of ambient temperature can be obtained by using temperature FBG.In the static test,after the sensor temperature compensation,there is no obvious displacement at the five monitoring points,indicating that the sensor system can carry out displacement monitoring work normally.The sensor can effectively monitor the abnormal displacement of soil under abnormal compression deformation,soil deformation during crack development and soil slope deformation under slope cutting. |
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