Development of an Overhauser Magnetometer with an Omnidirectional Sensor for Submarine Magnetic Field Observation

To achieve optimal measurement of the Earth's magnetic field at different latitudes when the attitude of the sensor changes, an omnidirectional sensor is necessary for marine magnetometers. A novel omnidirectional sensor consisting of primary and compensation coils is proposed to enhance omnidirectional performance. The primary coil consists of eight inclined coils with an inclined angle of 27° to generate both axial and radial magnetic field components, and two compensation coils are wound to enhance radial magnetic field components. With the compensation coils, the omnidirectional coefficient was successfully increased from 0.411 to 0.485 through theoretical calculations. Experimentally, the measured omnidirectional coefficient was 0.477, which is in agreement with the theoretical result. The performance of the omnidirectional sensor was estimated in a controlled artificial magnetic field. For the worst case, the peak-to-peak amplitudes of the Larmor signal and sensitivity are 1.817 V and 0.018 nT@5s (sensitivity with a cycling rate of 5 s), respectively. For the best case, the peak-to-peak amplitudes of the Larmor signal and sensitivity are 3.808 V and 0.004 nT@5s, respectively.