Research On Performance Enhancecment Of Coupled Core Fluxgate Sensor Based On State Feedback And Injection Locking

Detection technology of weak magnetic field which plays a crucial role in the fields of mineral resource exploration,space scientific research,earthquake observation,national defence and military early warning,is one of the core technologies related to people's livelihood and national security.Moreover,the high sensitivity,low noise magnetic field sensing method is the premise of weak magnetic field detection.At present,among various vector magnetic-field sensing technologies,the fluxgate sensor is considered to be the best all-around magnetic sensing technology due to its balanced advantages in cost,volume,performances,Etc..It has become an indispensable weak-magnetic detection means.Although the fluxgate technology has been researched and developed for nearly a century,there is still a big gap between its current achievement and its performance potential.In 2003,a scientific research group affiliated to the US Naval Information Warfare Systems Command(NAVWAR)proposed the coupled core fluxgate(CCFG)sensing technology based on the stochastic resonance.This sensing technology combines the characteristics of coupling induced oscillation in nonlinear systems,whose sensitivity is beyond the reach of the single-core fluxgate technology.And it has the great potential to further improve the performances of fluxgate sensors due to its extraordinary sensitivity in magnetic-field sensing.Since its development,the global scientific research team integrating theoretical research(NAVWAR),method application(University of Warwick),and technology realization(University of Catania)have been established,and the theoretical system construction and prototype realization of the CCFG technology have been basically completed,and the overall progress is in an ascending stage.In contrast,although domestic research teams have conducted related research on stochastic resonance theory in fluxgate phenomenon,we have not yet formed a complete theoretical system.We are still in the initial stage of pre-research,and there is a true gap between foreign groups and us.In order to build a complete research system of CCFG sensing technology,narrow the gap with foreign groups,and further improve the measurement performances of fluxgate magnetometers,this dissertation will focus on the theoretical studies,method utilization,and hardware optimizations.On the basis of learning and understanding the theory of coupled core fluxgate sensing,applying state feedback and self-frequency injection locking to achieve sensor sensitivity enhancement and noise elimination,furthermore performing magnetic crosstalk suppression and close-loop detection through the optimization of component arrangement and detection method,and finally complete the construction of the CCFG magnetometer and realize the improvement of the sensor's performances.Based on the above research schemes,the main contents of this thesis are as follows:(1)The theoretical analysis and prototype construction of CCFG.Essentially,the CCFG sensing technology is the application of dynamic characteristics of soft magnetic materials.The nonlinear bistable characteristics of the magnetic core are analyzed based on the dynamic model of soft magnetic materials.And according to the coupling topology of CCFG system,the dynamic expression of the coupling system is built,and the characteristics and critical conditions of the coupling-induced oscillation are studied by bifurcation analysis.Based on the waveform pattern obtained from the experiments,the CCFG numerical simulation model is built through regression fitting.After the theoretical study of CCFG sensing technology,we built the first domestic prototype of the CCFG magnetic sensor through the analysis,implementation and optimization of soft magnetic material of fluxgate core,probe structure,coupling topology,detection scheme,Etc..This part provides basic theoretical support and experimental test objects for subsequent research.(2)State feedback utilized for sensor sensitivity enhancement.The sensitivity expression of the CCFG magnetic sensor and its influencing factors are studied,and the control law of the state feedback is studied,and the physical realization is carried out.Through the means of numerical simulation and experimental testing,the influence law of state feedback on the oscillation characteristics and sensor sensitivity is obtained.The test results show that the state feedback can effectively control the critical coupling strength,thereby achieve significant enhancement on sensor sensitivity.Finally,the sensor sensitivity increases from 0.0253?s/n T to 0.7895?s/n T.(3)Injection locking implemented for sensor noise optimization.The theory of injection locking is learned and combined with the CCFG system,and the influence of frequency offset and amplitude on the working regime of the coupling system is studied.Numerical simulations have verified the effect of injection locking on the frequency stabilization and phase locking of the coupling-induced oscillation.The physical realization of injection locking is designed and tested.The test results show that injection locking can efficiently improve the detection resolution.Without the state feedback,the resolution has been improved from 395 p T to 70 p T.(4)Magnetic crosstalk suppression between adjacent fluxgate elements.The influence of magnetic crosstalk on the oscillation characteristics and sensor performances is analyzed.The conventional horizontal arrangement and the proposed vertical arrangement are evaluated by means of finite-element simulation.And a CCFG probe with the vertical arrangement is built,and its magnetic crosstalk is evaluated in the electro-magnetic shielding room.The simulation and experimental results show that the vertical arrangement can effectively reduce the magnetic crosstalk,and at the same time make the probe size smaller.(5)The close-loop flux detection based on residence times difference method.The analog circuit implementation of the residence times difference method is designed,and the flux feedback detection method is proposed,which realizes the close-loop detection of the magnetic field.And the balance detetion scheme makes the magnetic core in the zero magnetic state,avoiding the inherent defects due to the non-zero working regime.The final design of the CCFG magmetometer is completed and experimental tests are carried out.The test results show that the noise level of the self-built fluxgate sensor is about 20 p T/?Hz at 1Hz frequency point,which basically reaches the level of the current mainstream fluxgate sensor(Mag-03 basic version from Bartington Inc.).Finally,through the above research,the method for detection performances enhancement of fluxgate magnetic sensor based on coupling-induced oscillation is formed,and the construction and performances test of the CCFG magnetometer is completed.And the sensor basically reaches the noise level of current mainstream fluxgate magnetic sensors.In addition,based on the self-built CCFG magnetic sensor,a successful attempt is made to measurethe magnetic field interference induced by the subway,which initially verifies the sensor applicability.This dissertation studies the coupled-core fluxgate sensing technology from theoretical study,method utilization,hardware optimization,etc.,forming a complete research system,narrowing the gap with foreign scientific research groups,and improving the performances of fluxgate sensors.The improvement provides a feasible direction and lays a solid foundation for domestic research on CCFG sensing technology.