Research On Low Frequency Vibration Sensor Based On Optical Fiber Macro Bending

The COVID-19 pandemic is raging,the health of quarantined people is an urgent concern because of the shortage of medical staff.The human heartbeat is a low-frequency vibration signal.The low-frequency vibration sensor can measure the heartbeat signal and monitor the health status of quarantined personnel.During the epidemic,the lockdown zone is large,there are many quarantined people,and the environment is complex and changeable.Therefore,a large number of vibration sensors are needed,which requires that the cost of vibration sensors should be low enough and be able to cope with the complex environment.Fiber optic sensors have the advantages of corrosion resistance,electromagnetic interference resistance and high sensitivity,and are widely used in vibration detection in complex environments.Traditional optical fiber sensors mainly use wavelength modulation,whose demodulation system is complex and cost is high;the phase modulation vibration sensor is based on the interferometer structure,which is easy to be affected by the outside world and has a low signal-noise ratio;the intensity modulation sensor has simple structure and easy demodulation,which is suitable for low cost and complex application scenarios.However,the existing intensity modulation sensor has the problems of low sensitivity and poor structural stability.In view of the above problems,this paper designs a low frequency vibration sensor based on fiber macro bend for low cost and complex application scenarios.The main research contents are as follows:(1)Simulation analysis and experimental research on single mode fiber bending loss.Analyze the principle of bending loss of fiber,study the bending loss mechanism of single mode fiber;analyze the relationship between bending loss and core radius of single mode fiber through simulation,test the bending loss of single mode fiber with small core diameter;select the sensing fiber that can improve the sensitivity of intensity modulated fiber vibration sensor according to the simulation analysis and experimental test results.(2)Design and fabrication of fiber macro bending low frequency vibration sensor.Analyze the sensing principle of fiber macro bending low frequency vibration sensor;design sensing element based on fiber macro bending arc structure;explore the relationship between bending loss and bending radius of single mode fiber through simulation analysis and experimental test,select the bending radius of macro bending arc structure;design of sensor mechanical structure with low frequency response for sensor element,establish three dimensional model diagram of sensor structure through simulation software,complete the production of optical fiber macro bending low frequency vibration sensor.(3)Performance test and application of fiber macro bending low frequency vibration sensor.Test the sensitivity response of the sensor,get the sensitivity response curve of the sensor,and studied the sensitivity improvement effect of the fiber macro bending low frequency vibration sensor;test the amplitude and frequency response,get the amplitude frequency response curve of the sensor,analyze the natural frequency and operating frequency range of fiber macro bending low frequency vibration sensor;test the performance of fiber macro bending low frequency vibration sensor in practical application scenarios by measuring human heartbeat signal and gait signal.