Evaluating and enhancing the alternating current (ac) shielding performance of magnetic shielding cylinders (MSCs) is important to improve the sensitivity of magnetometers and the signal-to-noise ratio (SNR) of magnetocardiography (MCG). The dynamic radial shielding factor (RSF) of single-ended open MSC rapidly decreases with increasing frequency. To accurately analyze and improve the dynamic RSF, a high-performance and low-cost permalloy-nanocrystalline MSC (P-N-MSC) composite structure is innovatively proposed based on the analytical and finite element model (FEM) in this article. The structural reason why placing nanocrystals in the innermost layer of P-N-MSC performs significantly better than placing nanocrystals in the middle and outer layers is analyzed in detail through experiments and finite element simulations. The average dynamic RSF of P-N-MSC is 2.05 times higher than that of MSC among 0.5-95 Hz. The average noise at 0.5-95 Hz is reduced by 63.58%. This study provides a theoretical basis and technical support for constructing magnetic shielding devices with high magnetic shielding performance.

Magnetic shielding room (MSR) is one of the necessary equipment for measuring magnetocardiography (MCG) and magnetoencephalography (MEG). The traditional closed MSR only focuses on the indicators of the shielded magnetic field, and ignores the patient's feelings within the MSR. In this paper, an open-window MSR is proposed to solve the problem that patients have difficulty in communicating with the outside of closed MSR and have closed fear. The simulation results show that the size and distribution trend of the residual magnetic field in the inner working area of the MSR with shield-duct and active magnetic compensation coil is similar to that of the closed MSR. The method proposed in this paper provides a way to improve the comfort of patients in MSR for measuring MCG and MEG in humans.

The magnetoencephalography (MEG) measurement is important for diagnosing and treating brain functional diseases. MEG measurement based on the atomic magnetometer requires highly uniform and stable magnetic field environment, which is usually achieved by combining magnetic shielding room (MSR) and biplanar coils control system. However, the control effect heavily relies on the performance of the MSR. A hybrid control method based on dual-coil is proposed in this study, which reduces the dependence of the control effect on the MSR by actively adjusting the magnetic field distribution in the MSR and ensures high control accuracy based on the Rayleigh model relationship between the compensation coils and the MSR, better results can be achieved compared with the biplanar coils control system. The proposed method can provide certain reference for developing the active and passive combined magnetic shielding system with low cost and high performance for the MEG.

Magnetic field noise is a key factor limiting the resolution of quantum precise measurement. In active magnetic field compensation systems, the large coil constant and fixed noise of the coil and current source, respectively, cause excessive noise. This study proposes a differential biplanar coils (DBCs) design method by comprehensively optimizing two sets of biplanar coils with differential evolution (DE) algorithm, which can reduce the coil constant by two magnitude orders while ensuring high uniformity. The peak-to-peak magnetic field at the center point is reduced to 0.8 pT, and the magnetic field noise is reduced to 8 fT/Hz, which is a reduction of 94.4%. The low noise active magnetic compensation system based on the differential biplanar coils can improve the accuracy of the magnetic shielding room (MSR) internal magnetic field control and reduce magnetic field noise effectively. The proposed method contributes to generating a near-zero magnetic field environment with low magnetic field noise, which is critical to promoting magnetoencephalography (MEG) measurements.

The Magnetoencephalography (MEG) based on atomic magnetometer has high demand for the uniformity in the measurement area. Due to the door and holes of the magnetically shielding room (MSR), the distribution of residual magnetic field is non-linear, introducing much trouble into the magnetic field compensation. This study proposes a method for improving the uniformity of the residual magnetic field in the compact MSR by injecting different currents into the two coils in each pair of the outside compensation coils. The model and theoretical analysis method have been established, the feasibility has been verified both by the simulation and the experimental test. Results show that the maximum of the three components of the residual magnetic field in the direction of the three axes can be reduced by 18 times, 10.6 times and 8.1 times, respectively, when compared with the results without compensation, and 2.4 times, 2.3 times and 2.2 times, respectively, when compared with the results compensated with the same current. This study can provide certain help for achieving ultra-weak magnetic environment with high uniformity for the MEG measurement Note to Practitioners —In this article, we focus on the problem of compensating the residual magnetic field in the compact MSR with high efficiency and low cost, which remains the key factor that limits the promotion of the MEG. Method based on the compensation coils in series outside the MSR only deals with the linear or symmetric components, but has nothing to do with the non-linear and asymmetric one caused by the door. We propose a new method for compensating the residual magnetic field based on the coupling between the active and passive shielding, high compensation efficiency and uniformity can be achieved. In future work, we will aim at applying this method to create an ultra-weak magnetic field environment with high uniformity for the MEG measurement.

Active magnetic compensation technology can effectively reduce magnetic field disturbances within a magnetic shielding room (MSR) and improve the signal-to-noise ratio of magnetoencephalography (MEG) measurement. But, for small-sized MSRs with external compensation coils, achieving high-precision magnetic field control is challenging, because it is difficult to establish an accurate mathematical model. In this article, an active magnetic compensation system is constructed based on model-free adaptive control with a radial basis function neural network (MFAC-RBFNN) method, which addresses the limitations of magnetic field control accuracy caused by the requirement for precise system model information. The nonlinear and coupling characteristics of the active magnetic compensation system were analyzed, and a model-free adaptive control (MFAC) controller is designed based on the input current and output magnetic field, and the utilization of radial basis function neural network (RBFNN) for estimating magnetic field disturbances. The experimental results are given to prove that the algorithm proposed can achieve high-precision control of magnetic field within the MSR without an accurate system model, and compared with proportional-integral-derivative (PID), the magnetic field disturbance reduction effect is improved by 2.4x. It contributes to generating a near-zero magnetic field environment with low magnetic field disturbance.

The mass imbalance of the rotor will produce the synchronous vibration force that is transmitted to the magnetically suspended control moment gyroscope (MSCMG) through the magnetic levitation stator, which affects the imaging performance of the satellite. The suppression of the synchronous vibration force needs the speed signal. In order to solve the synchronous vibration force of the MSCMG when the speed measurement sensor fails, this article proposed an modified double second-order generalized integral frequency-locked loop (SOGI-FLL) method, which uses the frequency of the disturbance signal generated through the mass imbalance of the rotor to adaptively estimate the rotor speed and suppress the synchronous vibration force generated by the active magnetic bearing system. The phase compensation is introduced to ensure the stability of the system in full frequency band. The electromagnetic force is directly used as the input signal of the control algorithm to achieve zero magnetic force control. Simulation and experiment are carried out, and the results are given to prove that the algorithm proposed in this article can accurately estimate the rotation speed and achieve the vibration force suppression in the full rotation speed range. It is of great significance for the high-precision control of the active magnetic bearing (AMB) rotor system.

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.

This study proposes a hybrid method for improving the magnetic shielding performance of a magnetic shielding room (MSR) with few permalloy layers. In this method, two types of compensating coils are combined, one placed outside the MSR and the other placed inside. The coupling effect between the outside coil and the permalloy layer is used to adjust the residual field distribution characteristics of the MSR, and the inside coil is used to compensate for the adjusted residual field. This method has been verified with an MSR with two permalloy layers and an inner space of 1.3 × 1.3 × 2.2 m. According to the result, the residual field was reduced to less than 2.5 nT in a cube with a 0.4-m side length, which is seven times lower than that without compensation, and the inner space utilization rate was also improved by two times compared with existing MSRs with a comparable space size. The proposed method is of great significance in the development of magnetic shielding technology.

In rotating machinery, the rotor mass unbalance will cause synchronous vibration, in which static unbalance will produce synchronous vibration force, and dynamic unbalance will produce synchronous vibration moment. In order to suppress the vibration moment of the magnetically suspended control moment gyro, a modified dual-channel notch filter (DNF) is proposed in this article. First, the modeling of the rotor system with mass unbalance is performed. Then, the design of modified DNF is carried out. This notch filter uses the equivalent vibration moment calculated by the current and displacement signals as input, and uses the orthogonal characteristics of the moment signals in the X and Y directions to enter the controller at the same time. The stability of the rotor system with a DNF is proven. Finally, the experimental results are given to show that this method can effectively eliminate the synchronous vibration moment in the rotor system.

The active magnetic bearing rotor in magnetically suspended control moment gyro (MSCMG) will produce unbalance vibration due to the mass unbalance, and the frequency equal to the rotation speed. In order to suppress the unbalance vibration of MSCMG, the working principle of the active magnetic bearing (AMB) is introduced and the unbalance vibration model is established. And then, a high-precision closed-loop detection method of the synchronous signal based on synchronous rotating frame transformation (SRFT) is proposed. This method can detected synchronous signals in two directions at the same time, with less calculations. The synchronous current is suppressed by detecting and compensating the synchronous component in the output signal of the displacement sensor, which can reduce most of unbalance vibration. The phase modulation angle is introduced to make the algorithm have a wider stable range. In order to simplify the analysis method, the orthogonal characteristic of the output signal of the displacement sensor is used to equalize the dual output system to a complex-coefficients single-input system, and the dual frequency Bode diagram is used to analyze and evaluate the stability of the system. Finally, experimental results are given to verify that this method can effectively suppress synchronous current.

Magnetically suspended control moment gyro (MSCMG) is used in high-performance satellite platforms such as ultraquiet and ultrastable satellite. However, due to the unbalanced mass and sensor runout, the harmonic vibrations of synchronous and multifrequency will be generated, which will affect satellite performance. Aiming at the problem of harmonic vibration suppression of MSCMG, this article proposes a control algorithm based on multisynchronous rotating frame transformation. The electromagnetic force of the active magnetic bearing in MSCMG is directly used as the input signal of the control algorithm to achieve zero magnetic force control. This algorithm uses the orthogonal characteristics of the output signals of the X-direction and Y-direction displacement sensors. The vibration force in both directions can be suppressed by one controller simultaneously, saving the computing resources and having a faster response speed. The stability of the proposed method and the robustness to frequency fluctuations are analyzed. By changing the phase compensation angle in different frequency ranges, the stability of the system in the whole frequency band is ensured. Finally, experimental results are given to verify that the proposed method can achieve high precision and fast response suppression of harmonic vibration.

The rotor mass imbalance and sensor runout will cause the harmonic vibration of active magnetic bearing system. Repetitive control (RC) can effectively eliminate periodic disturbances. When the vibration frequency fluctuates, the performance of conventional repetitive control (CRC) becomes worse, and it is difficult to deal with the situation that the ratio of fundamental period to sampling period is a fraction. Therefore, the virtual sampling second-order repetitive control (VSSRC) is designed. Virtual sampling can ensure that the ratio of the fundamental period to the sampling period is an integer without changing the physical sampling frequency. The second-order repetitive control (SRC) can enhance the robustness of the system and maintain a good suppression effect even when the frequency fluctuates. The experimental results of AMB system show that the suppression effect of VSSRC is better than that of CRC when the frequency fluctuates. This research on the micro-vibration of the rotor is of great significance and application value.