Interference Optical Fiber Distributed Seismic Wave Detection System

An earthquake is a natural disaster with great destructive power.In addition to the direct disaster caused by the earthquake,the secondary disaster caused by the earthquake cannot be underestimated.Therefore,the use of relevant instruments to monitor seismic wave signals in real time and transmit them in a distributed form is of great significance to the development of human society.Traditional electrical geophones generally have good detection capabilities,but there are problems that are difficult to solve,such as weak anti-electromagnetic interference ability,narrow frequency response range,large mechanical structure,and high cost.Compared with traditional electrical detectors,fiber optic detectors have outstanding advantages such as corrosion resistance,electromagnetic interference resistance,high sensitivity,wide response range and easy integration.In this paper,combining the advantages of several optical fiber systems,a set of M-Z and ?-OTDR fusion distributed seismic wave monitoring system combined with mandrel elastic body is built.This kind of seismic detection system can also be used in petroleum exploration and border security and other fields.The main work of this paper is as follows:1.Compared with the defects of traditional electrical geophones,through the analysis of the mechanism of the strong detection system and detection structure in the field of optical fiber sensing,the MZ interference detection structure combined with the mandrel-shaped elastic body is selected as the research object of this article,and The conversion between the phase amplitude of the interferometer and the acceleration amplitude of the seismic wave signal is theoretically analyzed.In order to make the system built later have stronger positioning capabilities and lower engineering application costs,the positioning principles of the double-ended MZ structure and the ?-OTDR optical path structure are respectively analyzed,and the ?-OTDR optical path is selected as the interferometric optical fiber distributed monitoring The positioning structure of the system.2.In order to verify the sensitivity response ability of different transducer structures to low-frequency seismic wave signals,through the selection of structural material parameters,finite element displacement analysis and sensitivity test experiments were carried out on the two transducer structures designed in this paper.The results show that the maximum response sensitivities of the two structures are 11102.5 rad/g and 14551.33 rad/g,respectively,which verifies the better detection ability of the mandrel-type transducer structure for low-frequency seismic signals.The mandrel-shaped structure has been tested for lateral sensitivity to verify its good directional performance,which provides a theoretical basis for its application in three-component applications.3.Designed and built a M-Z and ?-OTDR fusion distributed seismic wave monitoring system,and made a reasonable selection of components.An improved closed-loop demodulation method of fundamental frequency mixing is proposed.Through phase demodulation test,good demodulation results are obtained in both time domain and frequency domain.Finally,through two sets of test experiments with different amplitude signals in different environments,it verifies the excellent monitoring ability of the interferometric fiber distributed seismic wave detection system for low-frequency signals.