Four-peak tracking autonomous omni-directional CPT atomic magnetometer
Abstract
<p indent="0mm">Omni-directional measurement of the geomagnetic field in satellites is necessary. Coherent population trapping (CPT) atomic magnetometer is theoretically capable of omni-directional measurement of magnetic fields, but it requires a reference signal in the direction of the magnetic field. To solve this problem, a new control method was proposed in this paper to trap four CPT signals. First, the control system demodulates the CPT differential signals with <italic>n</italic>=–3, <italic>n</italic>=–2, <italic>n</italic>=+2, and <italic>n</italic>=+3 by a time-division frequency modulation. Second, these CPT differential signals are fused to obtain two new feedback signals: one feedback signal used to calibrate the central frequency between <italic>n</italic>=±2 or <italic>n</italic>=±3, and the other feedback signal used to adjust the frequency between the central frequency and the CPT signals with <italic>n</italic>=±2 or <italic>n</italic>=±3. When a change in the magnetic field direction causes CPT signals with <italic>n</italic>=±2 or ±3 to disappear, the two feedback signals remain unaffected. Therefore, this control method does not require a fluxgate magnetometer to provide the magnetic field direction for mode switching and can obtain continuous magnetic data without losing lock in the range of 0°–360°. This means that it is an autonomous omni-directional CPT atomic magnetometer.</p>
