Research On Strain Sensing Technology Based On Bragg Fiber Grating

At present,the increasing emphasis on health monitoring of structures in various industries,it is critical to select a appropriate sensing technology.Bragg fiber optical grating compared to the traditional electrical sensors have the advantages of strong resistance to electromagnetic interference,easy networking,low optical signal transmission loss and so on.Strain distribution in important parts of a structure can accurately reflect its health condition.In this paper,strain sensing technology based on Bragg fiber grating is studied,and the main work is as follows:1.The strain sensing mechanism of fiber grating is studied,and the strain sensing model is established by using Matlab to simulate the linear relationship between strain and Bragg center wavelength.Four typical fiber grating demodulation techniques were studied,and the FP tunable filter demodulation method was selected suiTab.for this topic by comparative analysis.Aiming at the problem of unsTab.performance of the traditional F-P filter demodulation method,the fiber etalon was used to calibrate the F-P filter.With the calibration method,the linearity of the fitted curve was improved from 0.96 to 0.9976,and the strain demodulation accuracy was improved from 17%to 2%.2.The fiber grating demodulation system was designed,including optical path structure design,hardware circuit design and software logic design.In the optical path part,the optical path structure based on the calibration of etalon was designed;The hardware circuit part designed the power supply circuit of the demodulation,FPGA peripheral configuration circuit,F-P driver source circuit,photoelectric detection circuit and signal conditioning acquisition circuit;The software part designed the logic of the triangle wave generation module and the logic of the AD acquisition control module based on the DDS principle.3.The spectral data processing methods of digital filtering,threshold setting,and peakseeking algorithms were studied.The digital filter was used to filter out the noise in the spectrum to make the sensor reflection peak smoother.And set an appropriate threshold,filter out the useless information at the bottom of the spectrum and retain the spectrum above the threshold.A peak-seeking algorithm is used to demodulate the center wavelength of the reflection peak.Compared with the four peak-seeking algorithms in the experiment,the Gaussian fitting algorithm is the most stable.,and the peak-seeking error is within ± 2pm.4.The sensitization package of fiber grating was designed,and the "I" package and the sensitization package were simulated and compared by Ansys,and it was concluded that the sensitivity of the sensitization package to the strain is 12 times higher than that of the "I"package.The fiber grating strain sensor was fabricated by studying the packaging process of the substrate structure and bare fiber grating.5.The experimental platform was built,calibrated the F-P filter with the etalon.The relationship between the driving voltage of the F-P filter and the scanning wavelength were calibrated.The linear fit was compared with the quadratic polynomial fit,and the quadratic polynomial with higher accuracy was selected to fit.The cantilever beam was used to calibrate the strain of the sensor The designed fiber grating demodulation system and strain sensor were used to do five strain measurement experiments in the laboratory environment,and the strain measurement accuracy was better than 2%in the measurement range of-3000με-+3000με.