四峰跟踪自主全向适应CPT原子磁力仪

Four-peak tracking autonomous omni-directional CPT atomic magnetometer

卫星上测量地球磁场要求高精度的原子磁力仪具有全向测量能力,多数的单探头原子磁力仪不具备这一能力,CPT原子磁力仪理论上具有全向测量能力,但目前仍需要外部磁场方向参考,不能自主实现磁场的全向测量.本文提出了一种CPT原子磁力仪的分时扫描四峰双闭环控制方法,通过循环扫描+2,–2,+3和–3级CPT信号峰获得开环输出信号,并将4个CPT峰的开环输出处理形成两路控制回路的误差信号,一路求和用于校准0级中心频率,一路差分用于跟踪锁定±2,±3级CPT信号峰与0级信号峰之间的微波频率差.当磁场方向变化导致平行模式对应的±2级CPT信号峰消失时,通过±3级CPT信号峰与0级信号峰之间的微波频率差获得磁场大小,反之亦然,可以保持磁测数据连续不失锁,不需要外部磁场方向参考,首次实现了CPT原子磁力仪自主的全向测量能力.

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 n=–3,n=–2,n=+2,and n=+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 n=±2 or n=±3,and the other feedback signal used to adjust the frequency between the central frequency and the CPT signals with n=±2 or n=±3.When a change in the magnetic field direction causes CPT signals with n=±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.