Research On A New Type Of Vibration Sensor Based On Special Fiber Grating

The Vibration signal detection has important applications in structural health monitoring,seismic wave detection oil and gas pipeline monitoring and other fields.Large civil engineering will inevitably cause structural damage to different degrees and types due to environmental load and fatigue influence.Most abnormal and damaged failures of these facilities can cause structural vibration,and the detection of vibration signals can guarantee structural stability.In the field of seismic exploration,the structure of the crust and medium changes are analyzed by manually manufacturing sources and obtaining vibration information through sensors,which has great implications for oil and gas exploration,groundwater exploration and civil construction.In pipeline transportation,oil and natural gas and other energy sources are mainly transported through oil and gas pipelines.Punched oil theft or oil leakage will generate a vibration signal in the pipeline,and the real-time monitoring of the oil transmission pipeline can effectively avoid such events.Compared with electric vibration sensors,optical fiber Bragg grating vibration acceleration sensor has many advantages of small volume,high temperature resistance,electromagnetic interference resistance,light weight,corrosion resistance,strong reuse ability and many so on.Therefore,it has a broad application prospect.The miniaturization and orientation recognition of optical fiber grating vibration sensors have been the hot spots.In some special application scenarios for seismic exploration,only sensors that are small enough to achieve the desired measurements.In structural health monitoring,small-size sensors are also easier to achieve embedded sensing.The seismic wave is the vector,requiring detecting the components of the seismic wave in each direction to obtain accurate formation information.The direction of the vibration signal should also be obtained in structural health monitoring.In the miniaturization study of optical fiber grating vibration acceleration sensor,the suspension core length of optical fiber vibration sensor is uncontrollable,limiting its application.Multi-core fiber grating vibration sensors with direction recognition mostly use the cantilever structure,which is difficult to reuse.Aiming at these two practical problems,this paper designed and produced two vibration acceleration sensors based on special fiber gratings.An independent long suspended core micro-nano grating vibration sensor based on corroded grapefruit-type photonic crystal fiber was fabricated.The controllable etching preparation process of the suspended core in the photonic crystal fiber was studied,realizing the controllable suspension length of core.Finally,the sensor was subjected to vibration test,and its amplitude-frequency characteristics were analyzed.A fiber optic vibration sensor based on a multi-core fiber grating was designed and fabricated,and its static characteristics and its dynamic response characteristics to vibration signals were studied.The experimental results show that the structure has a direction-dependent response to vibration signals,and the measured The sensitivity under the action of lateral force is 10.8 times that under the action of axial force.The micro-nano fiber vibration sensor with a long suspended core in the fiber proposed in this paper has a controllable length of the suspended core,which broadens the application range of this type of structure and can achieve a wider frequency band of vibration signal measurement.The overall structure is only the size of an optical fiber.It can be applied to vibration detection in small spaces.The proposed multi-core optical fiber vibration acceleration sensor based on lateral force has high sensitivity and direction recognition,which can be applied to two-dimensional vibration measurement.