Design Of Overhauser Magnetometer Based On ARM

Overhauser magnetometer has been widely used in geological survey,archaeological survey,resource exploration,military reconnaissance and other fields since its appearance in 1983.Unlike proton magnetometer,Overhauser magnetometer adopts dynamic nuclear polarization technology instead of constant magnetic field polarization.Especially in polarization circuit,Overhauser magnetometer uses both bias magnetic field and radio frequency magnetic field to polarize simultaneously.Based on Overhauser effect,the amplitude of proton precession signal is increased by 100 times,and the polarization saturation time of proton is shortened.Therefore,it has the outstanding advantages of low power consumption,high precision and high efficiency.At present,the related research of Overhauser magnetometer has been carried out in some domestic universities and scientific research institutions,and has achieved corresponding results,but the results are developed on the basis of new methods put forward by foreign countries,so it lags behind the developed countries in general.Based on the analysis of the research background of Overhauser magnetometer and the current situation at home and abroad,the design of Overhauser magnetometer system using dual core of ARM and FPGA is proposed.Firstly,in order to satisfy the high frequency magnetic field excitation requirements of OVH sensor,a high efficiency boost switching power supply circuit,a third harmonic crystal oscillator circuit with a frequency of 55.3 MHz and a class A power amplifier circuit with a power greater than 1.5 W are constructed.Secondly,aiming at the problem of long turn-off time of transceiver switching circuit,dual-channel MOSFET is introduced to optimize the switching circuit,so that the turn-off time can be controlled within 2 ms.Then,in order to obtain high quality FID signals,128 sets of capacitance value Auto-scanning tuning and state variable filter are used as pre-filter,supplemented by two or three bandpass filters with specific gain.The parameters of each part are optimized by theoretical calculation and software simulation.Finally,according to the requirement of magnetic measurement accuracy,a four-channel periodic frequency meter based on FPGA is designed around the dual-core system of ARM+FPGA.In view of the gross errors of frequency measurement data,an algorithm of removing gross errors by adaptive double mean square deviation threshold is proposed,and the algorithm program is written through ARM.In order to verify the performance of the Overhauser magnetometer system based on ARM,a series of tests were carried out in the laboratory environment.Through testing,the output power of RF circuit is more than 1.5W;the range of Q value of resonance circuit in the frequency range of FID signal is given;the feasibility and reliability of the preamble signal conditioning circuit are evaluated;the conclusion that the frequency resolution of frequency measurement by frequency meter combined with debonding algorithm(threshold is 0.5)is greater than 0.0002 Hz is obtained;finally,the source of system error is analyzed and the error fitting curve is drawn.Provides the basis for instrument calibration.The research in this paper improves the measurement accuracy and anti-interference ability of Overhauser magnetometer,which is of great significance and value for promoting the capability of independent research and development of magnetic exploration instruments in China.