Study On Geophone Based On Fiber Bragg Grating

In recent years, geophysical detecting technologies based on fiber Bragg grating(FBG) develop increasingly in the field of seismic wave detection, structural healthmonitoring, oil and gas exploration, underground pipeline monitoring. Currently, it isreported that geophysical detecting technologies based on FBG has been applied in theweaponry of United States and Russia. But domestic study about this technology isbasically still in the stage of theoretical and experimental research. Therefore expandingthe research of the fiber Bragg grating geophone technology has great significance inthe theory and the practical application.From the FBG based accelerometer and signal demodulation technologies to start,the papers propose a novel FBG demodulation technology based on grating matchingmethod and design two different structure geophones based FBG. Furthermore,theoretical analysis and experimental research has been completed respectively Themainly contents and results achieved in this paper are listed as below.1. A FBG demodulation technology based on grating matching method is proposed.What is more, the theoretical simulation and experimental validation are completed forthis demodulation technology program. The study shows that: matching demodulationmethod is feasible for it can accurately demodulate the vibration signal from the FBGbased geophone; Advantages of system optical path simple, high signal-to-noise ratioand good effect of the low-frequency range is reflected; For the characteristics ofdemodulating precisely, a greater dynamic range and can eliminate light fluctuationsand optical path loss factors, matched demodulation based on double fiber gratings ismore suitable for detecting signal from geophone base FBG2. A FBG geophone sensor technology program based on the cylinder embeddedstructure is proposed. It is completed that the overall design and production of thesensor system. The theoretical analysis and experimental testing prove the feasibility ofthis sensing scheme applying to the acceleration detection. The experimental resultsshow that: operating frequency range of this FBG geophone is5-200Hz; theacceleration sensitivity within the operating frequency range is about90pm/g,fluctuation is less than3pm/g; the linearity of output linear response is better than5%.3. A FBG geophone sensor technology program based on simply supported beamstructure is proposed. It is completed that the overall design and production of thesensor system. Three different thickness structure sensors are produced and theexperimental results are compared. The acceleration sensitivity and resonant frequencyof the three different sensors were: the sensitivity and resonant frequency of1mm beamis about210pm/g(fluctuation is less than5pm/g) and63Hz; the sensitivity and resonantfrequency of1.5mm beam is about80pm/g(fluctuation is less than3pm/g) and145Hz; the sensitivity and resonant frequency of1.8mm beam is about56pm/g(fluctuation isless than3pm/g) and190Hz. The output linearity of system is better than4%. Withinthe frequency range from5Hz to0.6times the resonant frequency, response of theacceleration sensitivity is flat.4. Try the geophysical signal detection test, detecting successfully the pulsevibration signal and artificial tapping vibration signal.