Study On Sensing Signal Demodulation System For Geophone Based On Fiber Grating

Seismic prospecting, whose measured signal is the artificial seismic waves, is the most effective method and widely used in the geophysical exploration. This method is mainly used for the exploration of oil, metals minerals, coal, engineering geology, hydrogeology and geothermal. With the maturing of fiber grating sensor technology, fiber Bragg grating(FBG) geophone is being applied in seismic exploration and draws more and more attention to its advantages of good reliability, anti-electromagnetic interference, corrosion-resistant, able to work under a complex chemical environment, and so on.The main content of this paper includes:The theory of seismic survey is researched, and the state of geophone is introduced. Then, the advantages and disadvantages of traditional geophone are analyzed. Lastly, the future developmental trend is indicated.FBG and its sensing theory are introduced systematically. The influences of temperature, strain and the cross sensitive of them are analyzed. In addition, key technologies of FBG sensing application are analyzed, whose merits and demerits are contrasted. Especially, the edge filter demodulation method is mainly introduced. That is just the demodulation method of this systemThe sensing geophone based on FBG is designed, and its dynamic and static characteristics and the sensitivity formula are analyzed. Then, the size parameters of the equi-intensity cantilever beam are optimized to get the optimal frequencies. Besides, to verify the validity of the theoretical calculation, ABAQUS simulation software is used.The demodulation system based on edge filter method is designed. The long period fiber grating is chosen as the edge filter, whose linear area is fitting. The main performance parameters of photoelectric detector are analyzed and tested. The preamplifier circuit and the divider circuit are designed, and then Multisim software is used to simulate the above two. The signal Express module provided by Lab VIEW is a data acquisition and processing software, which is applied to establish the working interface. Finally, experiments are carried out to test the whole system to verify the feasibility of demodulation system.