Research On JPM-4 Proton Precession Magnetometer

The proton precession magnetometer(PPM)is a scalar quantum magnetometer based on the hydrogen proton lamo precession in the earth’s total magnetic field.The sensitivity of the magnetometer is an important technical indicator reflecting the ability to detect small magnetic field changes,and is closely related to the signal-to-noise ratio(SNR).In this article,the classic PPM design is studied and discussed,including sensor and electronic design.The measured initial signal of the magnetometer is 2V,and the lateral relaxation time is 0.77 s.Four methods for evaluating the sensitivity of proton magnetometers under different interference environments are studied,including direct measurement method,high-pass filtering method,synchronization method and gradient method.The sensitivity estimation results show that the direct measurement method is susceptible to low-frequency and high-frequency interference.Due to high-frequency interference,the estimated standard deviation of the high-pass filtering method is large,and this method can be used as an evaluation standard for the degree of environmental interference.The synchronization method and gradient method have excellent ability to suppress all natural and man-made electromagnetic interference(EMI),and can be used as an evaluation method of magnetometer sensitivity.Observation of the long-term diurnal variation of the magnetic field by multiple magnetometers shows that the sensitivity of the JPM-4 proton magnetometer at the 5 s cycle rate reaches 0.05 nT for the synchronous method or the gradient method.Synchronization and gradient sensitivity estimation methods are very suitable for developers and magnetometer users to evaluate the performance of magnetometers.