Simulation Of Nuclear Spin Precession And Alkali Metal Atom Magnetometer In Nuclear Magnetic Resonance Gyroscope

Nuclear magnetic resonance gyroscope(NMR gyroscope)is based on Larmor precession of spin magnetic moment of atomic nucleus.The angular rate or angular displacement of the carrier can be obtained by measuring the change of Lannor precession frequency or phase observation value caused by the gyroscope rotating with the inertial reference frame.There are usually two kinds of closed-loop control schemes for signal processing and system control of NMR gyroscope.One is the closed-loop control method based on frequency locking,the other is the closed-loop control method based on phase control.Compared with the frequency locking control scheme,the phase control scheme has better dynamic characteristics and real-time performance.It can directly output gyro rotation angular displacement information without integral calculation,but it requires higher phase error and closed-loop delay performance of the closed-loop control system.In this paper,the control mechanism and the influence of phase error of NMR gyroscope based on phase control are analyzed theoretically and simulated.A closed-loop control scheme of NMR gyroscope based on phase control is proposed and verified by simulation.Taking the nuclear magnetic resonance gyroscope with 87Rb-129Xe as an example,the influence of the magnitude and phase of the transverse excitation magnetic field on the macroscopic magnetic moment Larmor precession of inert gas atoms in the gyroscope is analyzed based on the dynamic equation of the nuclear spin precession.The conditions for realizing the nuclear spin oscillation are discussed and the simulation model of the nuclear spin macroscopic magnetic moment precession is established.The simulation results are given.Based on phase control,the steady-state self-excited oscillation of spin precession,the extraction and unwrapping of gyro rotation angular displacement signal are realized.The theoretical analysis and simulation results show that the steady-state precession of 129Xe atom can be maintained when the phase of the transversely excited magnetic field keeps the same phase with the macro-magnetic moment y component phase.When the feedback magnetic field based on phase control has phase deviation,the gyro output error will accumulate over time,which seriously affects the gyro output performance.The magnitude of the exciting magnetic field affects the magnitude of the steady-state macro magnetic moment,which should be considered comprehensively in the design of gyroscopes.The dynamic equation of spin precession of alkali metal rubidium atom is analyzed.The principle of three-dimensional magnetic field measurement using alkali metal atom in situ magnetometer in NMR gyroscope is studied.The principle of magnetic field compensation is analyzed.The simulation model of alkali metal magnetometer is established and verified by simulation.The simulation results show that the magnetometer model can detect and extract the precession signal of inert gas atoms,separate the magnetic field compensation signal and realize in-situ magnetic field compensation.