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The method of laser far-detuned frequency locking is proposed based on a fiber Fabry–Perot cavity which transfers the ultra-stable atomic reference frequency stability to the target laser utilized for atomic sensors. The control transfer function of the closed-loop system is established to elucidate the process of perturbation suppression. It is illustrated that this method is robust against the disturbance to the laser and cavity by controlling the cavity with different parameters. After the long-term experimental test, the stability of the laser frequency locked on the fiber cavity achieves an Allan deviation of 9.9 × 10 − 11 and the detuning of the nearest atomic frequency resonance point is more than 200 GHz. Its stability and detuning value exceed previous reports. [ABSTRACT FROM AUTHOR]

This paper systematically studies the output noise model of the K-Rb-21Ne co-magnetometer and proposes the method for determining the optimal pump laser power density. The amplitude-frequency response and the equivalent model for each frequency band are obtained through the transfer function of the co-magnetometer. Based on the established model and considering the power spectral density characteristics of magnetic noise, the output noise equation is formulated. Consequently, the pump laser power density yielding minimal output noise is determined. Both experimental and simulation results indicate that the pump laser power density yielding minimal output noise is greater than the pump laser power density corresponding to the maximum scale factor. Moreover, when the co-magnetometer operates at the pump laser power density corresponding to the minimal output noise, the output noise can be reduced by approximately 25%, and the Allan variance reaches its optimal value. The optimal Allan variance at 180 °C and 190 °C are 0.01395°/h @100 s and 0.01329°/h @100 s, respectively. Therefore, this pump laser power density is designated as the optimal pump laser power density for the co-magnetometer. Finally, simulations are conducted to investigate the variation patterns of the optimal pump laser power density points and the minimum output noise under different density ratios and gas pressures. The theories and methods proposed in this paper provide significant reference value for selecting the optimal pump laser power density and suppressing magnetic noise in co-magnetometers. [ABSTRACT FROM AUTHOR]

Magnetically shielded rooms (MSRs) provide a near-zero field environment for magnetoencephalography (MEG) research. Due to the high cost of high-permeability materials and the weak shielding capability against low-frequency magnetic disturbance, it is necessary to further design active compensation coils combined with a closed-loop control system to achieve dynamic nulling of environmental magnetic disturbance. To enhance the performance of the dynamic nulling system, this paper proposes a novel controller design method based on Padé approximation and generalized active disturbance rejection control (GADRC). First, a precise closed-loop model of the dynamic nulling system is established. On this basis, the delay element of the optically pumped magnetometer (OPM) is approximated using the Padé approximation method, and the controller is designed within the GADRC framework. The system's stability and disturbance suppression capability are analyzed using frequency-domain methods. To validate the effectiveness of the proposed method, simulations and experiments are conducted, achieving a shielding factor greater than 40 dB at 0.1 Hz. After filtering out power frequency interference, the peak-to-peak field fluctuation is reduced from 320.3 pT to 1.8 pT. [ABSTRACT FROM AUTHOR]

Stochastic magnetic field noise has a non‐negligible negative impact on the performance of quantum precision measurement instruments such as spin‐exchange relaxation‐free (SERF) co‐magnetometer in terms of sensitivity and stability. Conventional magnetic field error analysis and suppression methods are not applicable to stochastic magnetic field noise. In this paper, a stochastic model of the SERF co‐magnetometer is proposed to analyze the mechanism of stochastic magnetic field noise. The mean and covariance propagation model of the SERF co‐magnetometer is given based on the stochasticity model and statistical principles. The analysis of simulation experiments reveals that reducing the longitudinal electron spin polarization can somewhat reduce the standard deviation of the system output caused by stochastic magnetic field noise. And the atomic ensembles are most resistant to stochastic magnetic field noise when the electron spin polarization strongly couples with the nuclear spin polarization. Finally, the experiments verified the above conclusions. In conclusion, this paper provides theoretical and experimental support for analyzing and suppressing the effect of stochastic magnetic field noise on the SERF co‐magnetometer, which is of great significance for improving the sensitivity and stability of the measurement. [ABSTRACT FROM AUTHOR]

The active magnetic bearing system exhibits mass imbalance and sensor runout which cause the system to generate harmonic vibration force and moment. Repetitive control is an effective method to eliminate such harmonic vibration. Traditional repetitive control will eliminate all of the harmonic frequency components. However, in a practical system, the odd harmonic components usually dominate. Meanwhile, the existing method only suppresses the vibration force in the magnetic bearing system, and there is little research on the suppression of moment. Aiming at these problems, the harmonic vibration moment of the active magnetic bearing system is taken as the control object. This study investigates a hybrid control method that combines a second-order odd harmonic repetitive control with finite-dimensional repetitive control. And the virtual variable sampling is applied to construct any virtual sampling period in the proposed method, which effectively solves the problem of non-integer delay of digital repetitive control. The stability of the active magnetic bearing system is analyzed. The experimental results show that this method has faster response speed and better robustness when the frequency fluctuates. [ABSTRACT FROM AUTHOR]

Permanent magnet synchronous motor always suffers from air gap field distortion and inverter nonlinearity, which lead to the harmonic components in motor currents. A resonant controller is a remarkable control method to eliminate periodic disturbance, whereas the conventional resonant controller is limited by narrow bandwidth and phase lag. This article presents a novel resonant controller with a precise phase compensation method for a permanent magnet synchronous motor to suppress the current harmonics. Based on the analysis of the current harmonic characteristics, the proposed resonant controller for rejecting a set of selected current harmonic components is plugged in the current loop, and it is parallel to the traditional proportional–integral controller. Furthermore, the stability analysis of the proposed resonant controller is investigated, and the parameters are tuned to get a satisfactory performance. Compared with the conventional resonant controller, the proposed resonant controller can achieve good steady-state performance, dynamic performance, and frequency adaptivity performance, simultaneously. Finally, the experimental results demonstrate the effectiveness of the proposed suppression scheme. [ABSTRACT FROM AUTHOR]

Repetitive controllers are widely used in rotor systems of magnetically suspended control moment gyro, which are responsible for suppressing harmonic current because of sensor runout and mass imbalance of the rotor. However, the rotation frequency of the rotor is not constant in industrial applications, and it is likely to fluctuate around the rotation frequency, which greatly affects the suppression effect of the repetitive controller on harmonic current. This article proposes a new repetitive control method with strong frequency robustness, which still has high suppression accuracy when the rotation frequency is fluctuant. This method is simulated and verified on the magnetically suspended rotor system, which has achieved better results than previous research. [ABSTRACT FROM AUTHOR]