Research On Key Technologies Of High Sinsitivity And Low Crosstalk Fiber-optic Vector Accelerometer

Accelerometer is widely used in inertial navigation,seismic monitoring,resource exploration,control monitoring and other fields.For different application fields,the performance requirements of accelerometer are also different.In the field of seismic monitoring,accelerometer with high sensitivity and high directivity is needed to monitor the tiny vibration of seismic precursor.However,the performance of traditional accelerometer has reached its limit and is difficult to meet the current requirements,which severely restricts the development of seismic observation.Therefore,the development of accelerometer with high sensitivity,high precision and high directivity in low frequency observation has become one of the key technologies.Compared with the traditional seismometer,the fiber optic accelerometer has higher sensitivity,wider measurement frequency band and larger dynamic range,which is expected to replace the traditional seismometer and become an important measurement tool for the new generation of seismic observation,precursor information acquisition and geophysical research.At present,there is still a gap between the sensitivity of current fiber-optic accelerometer with the requirements of seismic precursor observation.How to achieve high sensitivity and low crosstalk of fiber optic accelerometer becomes one of the key problems to promote the development of seismic observation technology.In this dissertation,we focused on the measurement sensitivity and transverse crosstalk of fiber optic vector accelerometer.The main is contants as follow:Firstly,we study the energy conversion structure of fiber optic accelerometer.The stress-strain distribution of sensitive optical fiber in disc and mandrel energy exchange structure is analyzed,and the theoretical models of acceleration sensitivity and resonant frequency of the accelerometer in the above energy exchange structure are established.The sensitivity and resonant frequency of the accelerometer are compared and studied via finite element method,and it is concluded that the dual-disc accelerometer is more advantageous when it is applied to highly sensitive very low frequency seismic observation.Secondly,the method of enhancing the measurement sensitivity of dual-disc accelerometer is studied via finite element method.The effects of the geometric size of the elastic disk,the material properties and the optical fiber distribution on the sensitivity and resonant frequency of the designed accelerometer are analyzed.Combined with the actual operability and the analysis of the above three directions,a comprehensive optimization scheme for improving the sensitivity of the fiber optic accelerometer is proposed under the condition of ensuring that the designed sensor meets the requirements of the seismic observation frequency band.Thirdly,we build the theoretical model of transverse crosstalk for the fiber optic accelerometers,and the influence of transverse stiffness and symmetry deviation on transverse crosstalk is analyzed.A new low-crosstalk dual-disk fiber optic accelerometer is designed and a sample is fabricated.The errors introduced by the test system in transverse crosstalk testing are analyzed,and the influence of the deviation of the test system and the deviation of the accelerometer is modeled,and a new transverse crosstalk testing method is established to eliminate the errors introduced by the test system.Last but not the least,we build the performance testing system test the performance of the designed high sensitivity and low crosstalk fiber optic vector accelerometer.The results show that the sensitivity of the sample fiber optic accelerometer is higher than 16200rad/g,resonance frequency reaches 250Hz,crosstalk reaches-62.43d B,and resolution is6.02ng/Hz^1/2@1Hz.The research work in this dissertation can not only optimize the performance of fiber optic accelerometer,but also design accelerometers with different performance parameters according to different application situations,which has a good guiding significance.