Abstract: A proton magnetometer is a type of geomagnetic field measuring instrument based on the Larmor precession effect. However, a proton magnetometer with a single sensor is easily affected by geomagnetic diurnal variation and environmental interference. To improve the measurement accuracy of the proton magnetometer, sensor design and system performance evaluation are studied. Firstly, based on MAXWELL electromagnetic simulation software, simulation models of four kinds of sensors are established, including solenoid, cylindrical coil, ring coil, and "8" coil, and the directivity and anti-interference ability of the four coils are analyzed. Finally, it is determined that the "8" coil is used as the sensor to build a proton magnetic gradiometer. Secondly, the single and differential measurement results based on the fourth-order difference and mean square error algorithms are evaluated to analyze the performance of the magnetic gradiometer. The experimental results show that the initial signal-to-noise ratio of the "8"coil sensor can reach 40 / 1, the sensitivity of the single-channel mode can reach 0. 054 nT, and the sensitivity of the dual-channel differential mode can reach 0. 071 nT even under strong interference conditions, which is √2 times that of the single-channel mode.

Key words: Larmor effect, proton magnetic gradiometer, sensitivity, sensor