| The main cause of casualties in earthquake rescue is that the structure of ruins that had been seriously damaged or even collapsed is disturbed by aftershocks or improper rescue methods,causing re-damage or even secondary collapse.Vibration measurement is an important index for post-earthquake rescue safety assessment and an important factor for the stability of various mechanical equipment,Bridges and buildings.For vibration signals with frequency below 50 Hz,such as underwater detection,earthquake monitoring,geological exploration,etc.,in the military field,the amplitude of vibration signals is small,and effective signals are easy to be ignored.General fiber Bragg grating vibration sensors cannot meet the measurement of low-frequency signals.At the same time,the influence of complex ambient temperature changes on the measurement environment of FBG cannot be ignored.In order to reduce the influence of temperature change on the vibration measurement,it is very important to improve the sensitivity of the sensor.The traditional fiber Bragg grating sensor is easily affected by the change of ambient temperature,in order to effectively reduce the influence of temperature change on the vibration measurement results,this paper proposes a fiber Bragg grating acceleration sensor with double fiber-cantilever beam structure.Two fiber Bragg grating-cantilever beam structure is selected for the sensor,and two fiber Bragg gratings can realize the differential compensation of temperature.The cantilever beamstructure is chosen because the resonance frequency sensitivity of the sensor is mutually restricted,and the low-frequency vibration signal can be measured effectively with high sensitivity.Complete of sensor with Solidworks software and ANSYS Workbench software modeling and numerical calculation,the static simulation analysis of the sensor and the modal analysis,get the left arm arm length and thickness of the cantilever beam structure under different parameters of the sensor should be variables and the first order modal,by comparing the simulation result,and combining the results with the actual demand to determine the optimal cantilever arm arm length and thickness of the structure parameters;Then the parts are cut according to the simulation analysis results,and the parts are made by polishing,cleaning and other steps,and then the acceleration sensor of double-fiber-cantilever structure is assembled.The vibration experiment system and temperature experiment system were built,and the assembled sensors were used for vibration experiment and temperature experiment,among which the vibration experiment included amplitude and frequency characteristic experiment,sensitivity experiment and cross disturbance experiment.The comparison between a single fiber and two fiber Bragg grating acceleration sensors is set up in the experiment.The results of comprehensive simulation and experimental data analysis show that the arm length of the cantilever beam of the sensor is 15.5mm and the thickness is 1.00 mm,and the sensor structure is optimized.However,considering the indentation in the structure design,the arm length of the sensor is selected to be 17.00 mm to make the real object.With completed sensor testing,get a double fiber-suspensi on motion sensor working band of 15 ~ 60 Hz,the sensitivity of 156.70 PM/g,orthogonal crosstalk is 23.68 dB,and single fiber Bragg grating acceleration sensor sensitivity of 111.87 PM/g,comparison results show that the double fiber-cantilever structure effectively decrease the temperature influence on the measurement of fiber grating,for fiber Bragg grating temperature sensor in the complex environment of a certain basis is provided for engineering application. |
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