An Orientation Sensitivity Suppression Method for an Overhauser Sensor Based on a Solenoid Coil

Earth magnetic field sensors are used to detect the geomagnetic field and are critical for research in the geosciences and in prospecting for mineral resources. Today, the Overhauser sensor is the most accurate scalar sensor among widely applied geomagnetic field sensors. However, the Overhauser sensor shows severe orientation sensitivity due to its solenoid induction coil. Hence, in mobile applications that use Overhauser sensors, the accuracy of geomagnetic field data is decreased because of this orientation sensitivity. This paper proposes a method of suppressing the orientation sensitivity of the Overhauser sensor from the perspectives of the sensor structure, signal conditioning circuit, and measurement algorithm. To address the problem of no signal output from the sensor in a certain orientation, the parameters of the solenoid coil are optimized. Moreover, we designed a frequency adaptive high-accuracy signal extraction method based on a closed-loop feedback strategy, to decrease the measurement error contributed by the signal conditioning circuit and frequency measurement algorithm. Finally, we implement a prototype device using the proposed method with the commercial instruments to characterize the performance of our prototype, and test the orientation sensitivity of the prototype in the standard magnetic metering station. Experimental results demonstrate that the proposed sensor can achieve high-accuracy measurement capabilities comparable to those of commercial instruments in any orientation, indicating that its orientation sensitivity is efficiently suppressed.