Study On Key Technologies Of FBG Accelerometers Based On Spring-mass Structures

With the tremendous development of the vector acoustic theory and the underwater acoustic vector detection system,vector hydrophones have been showing great superiority over scalar hydrophones as a kind of important sensors in the underwater acoustic detection area.Among them,interferometric fiber optic vector hydrophones have seen rapid improvement in recent ten years and been in the stage of array applications.But its size can not be reduced further because of the sizes of the interferometer elements and the sensor head structure.While optical fiber gratings have advantages of small size,low prime cost and easy to wavelength division multiplexing which makes it possible to develop miniaturized optical fiber grating vector hydrophones and extreme large scale optical fiber grating vector hydrophone arrays.In this paper,the research goals are to manufacture and analyze small size and high sensitivity optical fiber grating accelerometers and vector hydrophones aiming at vector hydrophone towed arrays application.Some key technologies of optical fiber grating accelerometers are researched.Taking optical fiber grating accelerometers as main research objects,this paper implements intensive study on four main parts which are accelerometer sensing model analysis,optical fiber grating signal processing technology,accelerometer sensor head technology and vector hydrophone application technology,respectively.The spring-mass type optical fiber grating accelerometer model based on push-pull structure is theoretically and simulantly analyzed.The theoretical expressions of the sensitivity and the resonant frequency are obtained.And the factors which influence the sensitivity are theoretically analyzed.The optical fiber grating demodulation system based on an unbalanced Michelson interferometer is designed.The key system parameters are theoretically studied based on which the optical fiber grating and the interferometer are analyzed and designed.The system dynamic range is theoretically analyzed.A fiber Bragg grating(FBG)accelerometer based on a radii-varying elastic cylinder is designed and its sensitivity enhancement are realized.Some miniaturized FBG accelerometers with different elastic shells based on the mass-embedded structure are designed and tested.The accelerometer size is reduced half whereas the sensor performance is not influenced.A three-dimension FBG accelerometer and the corresponding FBG vector hydrophone based on the discrete structure are designed and tested.The influence of an asymmetrical suspension system on triaxial signals' phase uniformity of vector hydrophones is theoretically and experimentally studied.The influence of nonzero floating force state of vector hydrophones on the system response is theoretically researched.The main achievement and innovation are as follows:1.A FBG accelerometer structure which can improve the sensor sensitivity base on the radii-varying elastic cylinder is proposed.The theoretical and simulation results indicate that the structure can improve the accelerometer sensitivity.In theory,the accelerometer sensitivity can be improved to 1.5 to 2 times of the original sensitivity under the given condition.2.A FBG accelerometer design idea based on the mass-embedded structure is proposed.This structure specially aims at FBG accelerometers based on elastic shells.It uses the inner space of the shells and reduce half of the axial size without influencing the accelerometer performance.The accelerometer based on a hollow lantern-shape aluminum shell has the best performance,its size is ?24mm×17mm,its sensitivity is 43.6pm/g,its resonant frequency is 1000 Hz,and its crosstalk is-15.3dB.3.The influence of an asymmetrical suspension system on triaxial signals' phase uniformity of vector hydrophones is theoretically and experimentally studied.The experimental results indicate that the suspension system has influence on the phase uniformity of vector hydrophones.A novel suspension structure is proposed which provides a new idea to design vector hydrophone towed arrays.