Research And Design Of Medium-low Frequency Vibration Sensor With Excessively Tilted Fiber Grating

In recent years,fiber Bragg gratings have occupied an important position in the field of sensing due to its many advantages such as anti-electromagnetic interference,corrosion resistance,high sensitivity,and small size.Various vibration sensors based on fiber Bragg gratings are widely used in aerospace,power grids,large-scale mechanical structure health monitoring and other fields.In order to meet the needs and practical applications of fiber Bragg grating vibration sensors with high sensitivity,easy demodulation,and low cost,the research of different sensitization structures,special packaging methods and the use of special fiber gratings to make fiber grating vibration sensors are still the current research hotspots at home and abroad.As a kind of special fiber grating,Excessively tilted fiber grating(ExTFG)has extremely low temperature cross-sensitivity effect compared with traditional Fiber Bragg grating(FBG)and Long period fiber grating(LPFG),and it has more advantages in the field of vibration sensing.This article aims to improve the performance of ExTFG vibration sensor and expand its measurement range.Two different types of vibration sensors based on reflective ExTFG are designed.First,the theoretical mechanical models of the two sensors are analyzed.Secondly,combined with ANSYS finite element analysis software,the modal analysis of the two sensors is carried out.Finally,the intensity demodulation method is used to conduct experimental research on the vibration sensing characteristics of the two sensors.The specific research content is as follows:(1)The related coupled mode theory of ExTFG is introduced,and the spectral response characteristics are theoretically analyzed.Secondly,the strain,bending,and vibration sensing characteristics of ExTFG are analyzed.Finally,the mechanical model of the vibration sensor is analyzed,and the feasibility of using different structures as the transducer element of the vibration sensor is theoretically analyzed.(2)A reflection type ExTFG cantilever beam vibration sensor is studied.First,through theoretical analysis of the sensor's vibration sensing characteristics,the feasibility of the reflection type ExTFG cantilever beam to measure vibration signals is theoretically analyzed.Secondly,use ANSYS finite element analysis software to analyze the modal and vibration shape of the sensor model.Finally,a reflection type ExTFG cantilever beam vibration sensor was fabricated and experimental research was carried out.The research results show that the resonance frequency and amplitude frequency response of the sensor can be adjusted by changing the length of the free end of the sensor;at the same time,the sensor has good linear response characteristics and dynamic response characteristics.Compared with the transmission type ExTFG and other intensity cantilever beam vibration sensors,its maximum acceleration sensitivity is increased by ?2.5 times,the TE and TM modes were 0.3 V/g and 0.26 V/g,respectively..(3)An ExTFG vibration sensor based on a symmetrical flexible hinge is studied.Firstly,it analyzes its working principle theoretically;Secondly,it uses ANSYS finite element analysis software to perform modal analysis on the sensor model,and obtains the mutual confirmation of the natural frequency value of the sensor and the theoretical calculation value;Finally,the vibration response characteristics of the sensor are experimentally studied.The experimental results show that the natural frequency of the sensor is 780 Hz,and the flat area of the amplitudefrequency response is 50-400 Hz.In addition,the acceleration has a good linear response.The linear acceleration sensitivity of the TE/TM mode is 302.89 m V/g and 257.08 m V/g,respectively.Under 1g acceleration,the SNR of the flat area(50-400Hz)is greater than 50 dB.