Overhauser Study On The Measurement Method Of Output Signal Of Proton Magnetometer

Overhauser magnetometer is a weak magnetic measurement instrument based on electron paramagnetic resonance and nuclear magnetic resonance.Because of its high precision,high sensitivity and low power consumption,it is widely used in archaeological exploration,mineral resources exploration,engineering environment exploration,object magnetic measurement and other fields.In China,the research on Overhauser magnetometer is still in the development stage,and there is a big gap in the accuracy,sensitivity,accuracy,magnetic measurement range and other indicators.In order to make the Overhauser magnetometer localized and industrialized,it is of far-reaching significance to strengthen the research of Overhauser magnetometer.Based on the project of "high precision Overhauser proton magnetometer R & D and industrialization" of Jilin Provincial Development and Reform Commission,this paper studies the output signal measurement of magnetometer:1.Through consulting a large number of relevant literature,the research significance and background of Overhauser magnetometer are introduced,the research status of Overhauser magnetometer is described,and the existing measurement methods of FID signal are analyzed.Based on the working principle and structure of Overhauser magnetometer,the specific research work of thispaper is determined.2.The signal-to-noise ratio of the FID signal output from the sensor in the probe of Overhauser magnetometer is low,so it cannot be directly used for frequency measurement,so it is necessary to improve the signal-to-noise ratio by means of capacitor harmonic matching circuit.In order to solve the problems of slow tuning speed and low precision of the existing harmonic distribution circuit,a fast tuning method based on multiple autocorrelation is proposed.Through the multiple autocorrelation operation and FFT transformation of the FID signal,the approximate frequency of the FID signal is obtained,and the corresponding harmonic capacitance is quickly selected.3.In view of the fixed frequency and exponential attenuation of the FID signal,the FID signal is preprocessed to meet the needs of digital frequency measurement.An amplifying filter shaping circuit is designed,which can amplify the amplitude of the FID signal,filter out the interference noise and shape it into a square wave.The output signal can meet the requirements of digital frequency measurement.4.In view of the shortcomings of the existing equal precision frequency measurement method of FID signal,such as low precision and no synchronization of standard signal,an improved equal precision frequency measurement method is proposed.By counting the rising edge and falling edge of the standard signal at the same time,the measurement accuracy is nearly 2 times higher than that of FID;In order to improve the measurement accuracy by increasing the measurement time,a multi-channel synchronous frequency measurement algorithm based on FPGA is designed to indirectly extend the frequency measurement time due to the limitation of the exponential attenuation of FID signal amplitude.Through the co simulation of software Quartus II and Modelsim,the results show that the multi-channel synchronous frequency measurement can reduce the frequency measurement error and improve the measurement accuracy without increasing the original frequency measurement time.