Investigations On Key Issues Of Magnetoresistance Based Triaxial Magnetic Sensors With High Performance

Emerging weak field application,such as unmanned aerial magnetic anti-submarine,geomagnetic navigation and bio-magnetic tag need high performance small three-axis magnetic sensor.Magnetoresistance(MR)is potential to be applied to above fields,but still suffered from problems such as 1/f noise,hysteresis and triaxial nonorthogonal problems.In view of these problems,this paper has carried out systematic research on the high-performance small-scale three-axis magnetic sensor from the aspects of magnetic field manipulation theory and determination method research,design and manufacturing,high resolution parameter estimation algorithm,integrated decoupling and calibration method and experimental evaluation under the support of National Natural Science Foundation Project,the main work and achievements are as follows:(1)A theory and method of magnetic field manipulation and sensing with micro-structure was presented.It provides a systematic solution to overcome 1/f noise,hysteresis and triaxial nonorthogonal problems.Utilizing electromagnetic theory and finite element stimulation to investigate magnetic flux vertical motion modulation,flux turning,magnetic field tracking and compensation.In which,flux modulation and magnetic field compensation theory is further developed into the theory of spatial magnetic field integration.The vertical(Z-direction)magnetic field is redirected to the X-Y plane with an integrated soft magnetic flux structure and achieved the planar measurement for 3D magnetic field with GMR sensor.Magnetic flux vertical motion which disturbs the magnetic field in air gap and induce a dynamic alternate current magnetic field,and 1/f noise suppression mechanism is reveal from spectrum shift of GMR signal.The influence of mechanical disturbance noise and quality factor on the stability of magnetic field manipulation was revealed.By rationally designing the quality factor of vibration structure,power consumption reduction and modulation efficiency improvement was achieved.Pulse magnetization can help GMR elements work at a stable original state,and the magnetization state of GMR elements can be roughly constant with tracking and compensating the detected magnetic field,for which magnetic hysteresis and nonlinearity will be suppressed.After modeling GMR output signal,parameter estimation of output signal was realized with FFT-based spectrum correction method,simulation results illustrate that the parameter estimation accuracy are related to sampling points,frequency bias and ratio of signal to noise.An integrated decoupling and calibration model was built and the influence of channel coupling error,channel inconsistency error and remanence and other non-ideal error were greatly reduced,the three-dimensional(3D)magnetic field measurement with high-precision was achieved.(2)Proposed a design scheme for the magnetoresistance based high-performance triaxial magnetic sensors,and built its optimization methods.Design and optimization of magnetic sensor system with high performance modulation structure and high-precision measurement and control system were presented.Based on the manipulation theory of micro structure,the magnetic sensitive elements,vertical motion modulation films,soft magnetic bulk for flux turning,micro compensation coils and micro silicon/PZT gyro-beam were integrated,which further improve and develop the design of triaxial magnetic sensor with high performance.According to damped vibration theory,quality factor of vibration structure was designed and optimized,simulation results shows that it has been improved to 737,which is 41 times higher than traditional schemes.The designed flux turning structure with efficiency of 62% and micro magnetic compensation coil with excitation coefficient is 1470.6nT/mA.By increasing the thermal conductivity of substrate material,power consumption of the system and damping of vibration structure are decreased,resulting in thermal effect reduction of the sensor,and the temperature rise is reduced from 17.9 to 2 degrees Celsius refer to simulation results.High accuracy vibration amplitude measurement and control were realized with orthogonal lock-in amplifier and digital PI control technology respectively.Bidirectional pulsed magnetization was used to reduce the hysteresis effect significantly.Combining with high resolution DAC and voltage controlled constant current source technology to achieve the high precision current control circuit.(3)Broke through some critical processes such as preparation of high performance modulation structure,high density micro compensation coil preparation,and high precision interconnect of the discrete microstructure with multi-physical characteristics at low temperature,and established a relatively complete manufacturing system for high performance triaxial magnetic sensing heads.By controlling the composition proportion of NiFe solution and electroplating current,high quality soft thick magnetic microstructure with large thickness was fabricated.Polishing the PZT ceramic with optimizing the rotation speed of grinding wheel,and with compensation of high-speed wheel cutting width to solve the roughness and brittleness problems.By optimizing electroplating parameters and adopting ion beam etching technology,the thickness consistency and vertical characteristics of the plating coil were improved,a high quality micro-compensation coil was fabricated;high-precision plane optical alignment was used to achieve high precision three-dimensional installation of GMR elements.Preparing the deep slot with photosensitive dry film and adopting Au-In eutectic bonding,the integrating bonding problems with small size bulk structures were solved,sequentially,low temperature interconnection of the PZT structures and the micro silicon structures were achieved.The shear strength with Au-In bonding could reach 12 Mpa or higher.By controlling the thickness of eutectic bonding layer,and using precision bi-direction CCD alignment,precision alignment of the triaxial magnetic sensing probe was realized.(4)Built the mathematical model of sensor output signal,and proposed its high resolution parameter estimation algorithm,then an integrated decoupling and calibration method was presented,and precise determination of triaxial magnetic field was achieved.Characteristics of the sensor output signal under different magnetic field frequency is investigate.A parameter estimation method based on zero-crossing and iterative spectrum correction was proposed for DC magnetic field measurement,which solves the problem that the traditional estimation algorithm can not take into account the accuracy and speed.A method based on determination factor inversion is proposed for low frequency AC magnetic field measurement,it overcome the restrict of frequency resolution problem due to spectral aliasing problem in the traditional DFT algorithm,and the frequency resolution of measured magnetic field reachs 0.8Hz.Aiming at the problems of triaxial magnetic information coupling and channel non-consistency,an integrated decoupling and calibration method based on the principle of vector magnetic field invariant was proposed.This method overcomes the limitation that classical total magnetic field invariant calibration methods require symmetry model,and integrated calibration and decoupling of magnetic sensor was achieved.(5)Established a serial of test and estimate methods for high performance triaxial magnetic sensors,roughly verified the magnetic manipulation and sensing theory,and some key indexes of magnetic prototype sensor are comparable to the latest reported level.The basic performance of the sensor hardware system was verified.Quality factor and amplitude-frequency characteristic of the resonant structure,thermal stability of sensing probe,response,noise and hysteresis of prototype sensor were measured and analyzed.The test results show that the quality factor of the resonant structure is beyond 400,the temperature rise of the probe is 1.9(2? ?),1/f noise reduction is about 230 times,the modulation efficiency is 31.45%,nonlinearity of prototype sensor is 0.13%,and the minimum detectable magnetic field reaches 126pT/?Hz,which is equivalent to the latest reported level.With the integrated decoupling and calibration processing,the turning efficiency of the sensor is measured to be 0.4,which is close to the design value(0.61),and the triaxial non-orthogonal error is 0.05°.