Gradient Tolerance Estimation of Overhauser Magnetometer

Abstract

Overhauser proton magnetometer is a scalar quantum device for total magnetic field measurement based on the dynamic nuclear polarization (DNP) effect. The earth generates a weak and uniform magnetic field about 18 μT to 60 μT. The magnetic anomaly in the survey area will generate a gradient magnetic field which decreases the accuracy of the magnetometer. The gradient tolerance is the maximum magnetic field gradient that the magnetometer can tolerate. A gradient coil consisting of two circular coils connected in reverse has been constructed to estimate gradient tolerance value of Overhauser magnetometer. The distance between the two circular coils is set as $\sqrt 3 $ R, where R is the radius of the circular. Calculated results indicate that the uniformity of the gradient can reach 99% in the range of 5×5×11 cm when the radius of the circular R is set as 0.3 m. Proton precession signal and sensitivity of Overhauser magnetometer under gradient field from 0 nT/m to 12000 nT/m are investigated. Beat phenomenon is observed under high gradient field. The experimental results show that under the background field strength of about 54500 nT, the fluctuation of the measurement results increases with the increase of the gradient.