Study On The Perfection And Evaluation Of The Performance Of Overhauser Magnetometer

Overhauser magnetometer is a scalar magnetometer measuring the total magnetic field based on dynamic nuclear polarization effect(DNP).With high sensitivity,high sampling rate,and low power consumption,it has been widely used in volcanology,earthquake prediction,military exploration,archaeological investigation and other fields.Our research group has developed the fourth-generation Overhauser magnetometer of JOM and developed a new type of working material that can work normally under low temperature conditions.This paper introduces the classification of magnetometer and the research status of Overhauser magnetometer at home and abroad firstly,expounds the working principle of the Overhauser magnetometer,the system composition and the process of realizing the test magnetic field,and analyzes and improves the system performance.The research is carried out from three aspects: sensor resonant cavity,system amplitude-frequency characteristics,and system noise.The Q value of the designed resonant cavity can reach 1100,and the uniformity of current distribution on the cavity is discussed;The influence of tuning capacitor on the amplitude-frequency characteristics of the resonant circuit is studied,and the actual amplitude-frequency characteristics of the actual signal conditioning circuit are tested for comparison with the theory.Combined with the system noise model,the relationship between noise figure and source impedance is analyzed,the actual voltage noise and current noise values in the system are tested,thus the actual noise figure of the system is obtained.In addition,the power of the RF excitation signal is set to 1W,and the Larmor signal received by the instrument when the new working solution is used in the sensor and the noise are tested on the campus of Jilin University.The signal-to-noise ratio can reach83:1.Finally,the performance specifications of the system are explored experimentally.For the sensitivity specification,the sensitivity estimation is obtained by combining the synchronous measurement method and the fourth-order difference method.In different electromagnetic interference environments,the synchronous method and the gradient method are used for sensitivity estimation.In general,the sensitivity estimation of the synchronous method and the gradient method is almost the same.Gradient instruments are used to carry out sensitivity experiments under different fast measurement periods;The drift problem of the JOM-4 Overhauser magnetometer is experimentally explored indoors,the drift is between ±0.01 n T,and the drift is small enough to be ignored;The magnetic measurement effect of the JOM-4 Overhauser magnetometer system composed of a new type of working solution under different magnetic field strengths and gradients is explored.The influencing factors of absolute accuracy are introduced,an evaluation method of absolute accuracy is proposed,the frequency measurement method is optimized,and the absolute accuracy of the mainframe of JOM-4 Overhauser magnetometer is improved.