Research Of Active Magnetic Compensation System For Atomic Magnetometers

The precision measuring of magnetic field is significant in the areas of geophysics,chemical analysis,military affairs,biomedicine,and materials science.Among the various technologies for magnetic field measuring,atomic magnetometers are the most sensitive magnetic sensors.The basic principle of atomic magnetometer is by measuring the Larmor precession frequency of atomic spins in the magnetic field to acquire its information.Nevertheless,atomic magnetometers should work under near-zero field(less than 10 nT)condition.In order to ensure the work conditions of magnetic field for atomic magnetometer,the methods of passive magnetic field shielding or active magnetic compensation are usually used to suppress background magnetic field.As to the method of passive magnetic field shielding,atomic magnetometers normally uses mu-metal to shield the background magnetic field.The magnetic shield made of mu-metal prevents the detection of outside magnetic field,which limits the application of atomic magnetometers in the fields of geomagnetic field detection,space magnetic field detection,and magnetic anomalies detection.In the method of active magnetic compensation,the background magnetic field is compensated by input current in coils.The most critical technique for active magnetic compensation is to suppress the power-frequency field noise and field gradient in the environment.Therefore,in order to solve these problems,a stable and effective algorithm in magnetic compensation system is required.In this thesis,a new magnetic compensation algorithm is proposed,and the development of an active magnetic compensation system based on the algorithm is comprehensively introduced.In addition,the research of Bell-Bloom type atomic magnetometer is also systematically described.This study mainly focuses on the following four parts:(1)The development of hardware for active magnetic compensation system.It mainly includes the compensation coils,the low noise magnetic measurement unit(noise 0.34 nT/Hz1/2),and the six-channel low noise current source(noise 30 ?A).(2)An innovative broadband magnetic compensation algorithm based on hyperfine spectrum analysis is proposed,which achieves the attenuation of power frequency magnetic field noise and magnetic field gradient by 36 dB of and 20 dB,respectively.(3)The synchronous compensation of multi-interference magnetic fields is realized,and the quasi-static magnetic field is attenuated by 111 dB.In addition,the experiment of signal extraction and quantitative evaluation in compensation process is carried out,and the error is about 1 nT.(4)The Bell-Bloom type atomic magnetometer is developed,and the sensitivity is 2 pT/Hz1/2.In summary,we have proposed a new magnetic compensation algorithm,and employed the active magnetic compensation system based on the algorithm to attenuate power-frequency magnetic field noise and magnetic field gradient by 36 dB and 20 dB,respectively.In addition,we have also developed the Bell-Bloom type atomic magnetometer,and the sensitivity is 2 pT/Hz1/2.We have solved the key technical problems that limit the measurement range of atomic magnetometers.This can greatly expand the application range of atomic magnetometers,which enables its promising applications in the areas of geophysics,chemical analysis,military,biomedicine,and materials science.