Research On FBG High-precision Sensing Method And Its Application Based On Intensity Ratio Algorithm

Fiber Bragg grating(FBG)sensors are largely used in all kinds of scopes thanks to its multiplexing ability and strong anti-electromagnetic interference capability.However,with the increasing demands for multi-point,wide-range and high-precision measurement in engineering,the traditional demodulation methods are limited by the full width half maximum(FWHM)of the FBG reflection spectrum,thus the accuracy is hard to be further improved.Aiming at this situation,this paper proposes a demodulation method of FBG Bragg wavelength based on intensity ratio algorithm,which greatly shortens the FWHM of FBG reflection spectrum and improves the demodulation precision of FBG Bragg wavelength.This demodulation method have broad application prospects in high-precision temperature measurement and in improving the multiplexing capability of the sensing channel.The main works done are as follows:1)The high-precision sensing method of FBG based on the intensity ratio algorithm is studied,the feasibility of the demodulation method is verified by MATLAB simulation,and the influences of modulation amplitude and sampling rate on the demodulation accuracy are explored.The periodic modulation module based on cantilever beam and exciter,the acquisition program based on LabVIEW and the data processing program based on MATLAB are independently completed.In addition,the effectiveness of the sensing method based on the intensity ratio algorithm in reducing the FWHM of the FBG reflection spectrum is explored.Finally,the FWHM of the FBG reflection spectrum is successfully compressed to 4 pm.2)As the temperature measurement accuracy of the traditional demodulation methods are limited by the FWHM of FBG reflection spectrum,the sensing method based on the intensity ratio algorithm proposed in this paper is used to carry out high-precision temperature measurement research.Compared with the reference FBG which directly demodulates the FBG reflection spectrum,the intensity ratio algorithm can improve the temperature measurement accuracy by 10.3 times.Based on this,the influences of sampling rate and modulation amplitude on temperature measurement accuracy are studied.Experiments show that when the modulation voltage amplitude is 2 V~3.5 V and the sampling rate is greater than 20 Hz,the average temperature measurement accuracy can reach ±0.015 °C.3)Aiming at the channel interval of adjacent sensors in wavelength division multiplexing(WDM)system is limited by the FWHM of FBG reflection spectrum,the intensity ratio demodulation algorithm is applied to the WDM sensing with multiple sensors in series.The periodic modulation device based on double cantilever beam is designed to realize the modulation of all FBG sensors in WDM system.By applying modulation in the opposite direction to adjacent sensors,the channel interval of 0.2 nm is realized,and the measurement range of external physical quantities such as temperature and strain are expanded.