Flux-controlled pulse demagnetization method for demagnetization equilibrium of magnetically shielded rooms
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摘要: 极弱磁场测量，如生命科学中使用的磁测量，需要近零磁环境，一般由高磁导率材料构成的磁屏蔽室提供。磁屏蔽室的性能可以通过消磁技术改善。常规的交流衰减消磁无法通过磁化状态评估快速确定并优化消磁参数；相较而言，脉冲消磁能通过磁链的测量和控制直接反映磁化状态。本研究提出了一种适用于磁屏蔽室消磁平衡的通量控制脉冲消磁方法，以实现消磁过程的精确调控。首先考虑损耗及环境磁场作用建立消磁等效电路模型，并引入磁链偏移量以修正控制参数；在此基础上测量磁屏蔽材料的磁性能，并建立磁屏蔽室的有限元模型以分析其理论性能极限。最后通过测试磁屏蔽室内部的实际残余磁场，证明该方法能在双层磁屏蔽室中心区域实现低至3.1 nT的平均残余磁场。Abstract:
Background Extremely weak magnetic field measurements in life science require near-zero magnetic environments, typically provided by magnetically shielded rooms (MSRs) constructed of high permeability materials. The shielding performance can be improved by demagnetization technologies.Purpose Conventional AC attenuation demagnetization does not allow for rapid determination and optimization of demagnetization parameters through magnetization state assessment. In contrast, pulse demagnetization can directly reflect the magnetization state through measuring and controlling the magnetic flux linkage. Therefore, this study proposes a flux-controlled pulse demagnetization method for MSR demagnetization equilibrium to regulate the demagnetization process precisely.Methods The equivalent circuit model is established by considering the losses and the ambient magnetic field, and the flux linkage offset is introduced to correct the control parameters. On this basis, the magnetic properties of the material are measured, and a finite element model of the MSR is established to analyze its theoretical performance limit.Results By testing the residual magnetic field inside the MSR, it has been demonstrated that this method can achieve an average residual magnetic field as low as 3.1 nT in the central area of the double-layer MSR.Conclusions The comparison with the conventional demagnetization can illustrate the improvement of pulse demagnetization in static magnetic shielding performance. The average residual magnetic field is improved by 46.6% for 120 complete demagnetization cycles. -
图 1 电路模型和消磁设备
Figure 1. Circuit model and demagnetization equipment for pulse demagnetization
图 2 消磁平衡过程中电压、电流、磁链同步变化示意图
Figure 2. (Schematic diagram) The applied voltage, the demagnetization current, and the flux linkage during demagnetization equilibrium
图 6 磁屏蔽室消磁过程电压、电流、磁链同步变化图
Figure 6. Synchronous changes in voltage, current, and flux linkage during the demagnetization process of the MSR with $ N=200 $
图 7 不同实验条件下的残余磁场分布图
Figure 7. Distribution of the residual magnetic field in the center area under different experimental conditions
表 1 残余磁场估算结果
Table 1. Estimation results of residual magnetic field
material property $ {B}_{\max } $/pT $ {B}_{\min } $ pT $ {B}_{\text{avg}} $ pT initial magnetization curve 5 600 3800 4200 anhysteresis magnetization curve 98 59 63 
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表 2 残余磁场平均值结果
Table 2. Results of average residual magnetic field
method average residual magnetic field/nT pulse demagnetization with $ N=200 $ 3.8 pulse demagnetization with $ N=220 $ 3.2 pulse demagnetization with $ N=240 $
AC attenuation demagnetization with $ N=240 $3.1
5.8
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