Research Of Monitoring Seismic Waves Methods Based On FBG

The earthquake is one of the most destructive natural disaster.It leads to a largenumber of casualties and huge amount of economic loss every year. How to forecast,predict and early warn earthquake has been the mission of the relevant science andtechnology workers. Seismic wave contains much earthquake parameters information,and it is able to realize early earthquake warning as well as to monitor seismicwaveform in real time according to its propagation velocity characteristics. Monitoringseismic wave based on FBG sensor is an important means for earthquake monitoring. Inthis background, the methods of seismic monitoring based on FBG are in-depthresearched in the thesis.Firstly, the mechanism between seismic wave and FBG sensor is analysedtheoretically in detail. The couped mode equations are reduced detailedly. Incombination with the characteristics of seismic wave, the mechanism between seismicwave and FBG sensor head is obtained under simple seismic waveform, which providesa theoretical support for the study of real-time seismic monitoring system based on FBGsensor. The transmission matrix theory for simulation analysis is derived according tocoupled mode theory. The simulation analysis of the relationship between the FBGspectrum and the grating parameters prove the feasibility of real-time monitoringseismic wave based on FBG.Secondly, two sets of real time monitoring seismic waves system based on FBGarray are proposed, the feasibility of the two demodulation schemes are analysed andproved theoretically. A optimized structure of the sensor head is proposed afteranalysing and designing the parameters of system, and the performance of the sensorhead is analysed theoretically. The FBG sensor head has enough frequency responserange through simulation. According to the output signal characteristics of seismic wavemonitoring system, photoelectric modules of the demodulation system based on a3×3coupler demodulation scheme is designed.Finally, a experimental system based on a3×3coupler demodulation scheme isbuilt. The experimental data is collected through the photoelectric modules, and then processed by using Matlab. The demodulation result is the same to the waveformobserved by oscilloscope in the sampling period. The results illustrate that thedemodulation scheme based on the3×3coupler for seismic wave monitoring systemwith FBG sensor has sensitive response to stress changes. The experiment result showsthe feasibility of real-time monitoring seismic wave based on FBG with a3×3couplerdemodulation scheme. The result lays a foundation for depth study of seismicmonitoring system using3×3coupler demodulation scheme based on FBG.