开放式磁场屏蔽系统研究

The precise measurement of magnetic field has great potential in the application of military, aerospace, medical, physical diagnosis. The major projects in 13th Five-Year of China's science and technology relates to various types of precision magnetic probe research. But the high ability of the probe does not mean that the high signal testing ability. Because the electromagnetic noise is becoming more complex with the large-scale layout of the urban subway and electric vehicle. Normally, the noise ratio is larger than the measured signal by 3~6 orders. Therefore, the magnetic shielding technology is necessary for the precision magnetic measurement. The traditional high permeability(u) room is widely used. But there is no optical path in the direction of noise fields, so high-u rooms have challenges for the protection of optical sensors and sensors requiring wireless transmission with the outsides. This project proposes a full open type magnetic shielding system. The new system uses dynamic compensation technology in collaboration with closed HTS coils. The new system intends to provide 50dB (99.7%) shielding factor in the frequency of 0~300KHz. This project aims to study the design theory, control algorithm, electromagnetic characteristics and engineering implementation methods of new shielding system, and to carry out compatibility research with protected objects. The research contents include: first, the electromagnetic inverse problem and collaborative control theory of the shielding system under the consideration of the superconducting flux penetrating process; second, study of shielding ability of the system in frequency spectrum and amplitude domain; third, processing method to realize the shielding system and compatibility study with precision measurement.

精密磁场测量在军事、航天、物理、医疗诊断领域应用前景巨大，我国十三五科技重大专项涉及多种类型精密磁探头研发。但探头磁场测试能力强，并不意味着信号测试能力强，这是因为随着城市地铁、电动汽车大规模布局，电磁噪音日益复杂，电磁噪比待测信号大3~6数量级。因此精密磁测量需要匹配磁屏蔽技术。传统高磁导磁屏蔽室应用广泛，但是是一种光学不透明的屏蔽方式，因此本项目提出一种全开放式磁屏蔽系统，系统基于动态补偿技术协同超导闭合线圈实现，拟在0~300KHz频段提供50dB（99.7%）屏蔽效能。 本项目拟对种新型屏蔽系统设计理论、控制算法、电磁特性和工程实现方法开展研究，并拟结合被保护对象开展兼容性研究。具体研究内容包括：第一，考虑超导磁通穿透微观过程条件下的屏蔽系统电磁场逆问题求解方法及协同控制理论；第二，研究系统频谱，幅域特性；第三，探索屏蔽系统的工艺实现方法，并与具体精密测量结合开展兼容性研究。

项目取得三项比较重要成果，第一、提出了AS-TS开放式磁场屏蔽系统，完成了磁场设计理论工作与解耦控制策略工作。系统可实现DC-10000Hz，50dB以上的广谱屏蔽，与传统的高磁导率屏蔽室的方案形成有效互补，为各类精密测量提供重要保障。这项技术理论工作发表在仪器仪表类知名期刊Review Scientific Instrument杂志上，技术已经与北京航空航天大学合作，目标为杭州极弱磁大科学装置提供0.1ft/Hz^0.5@1Hz的极限物理指标。第二、目组提出了一种超导体磁通穿透的快速算法，计算表明，利用该方法比目前国际上已知最快的T-A方法计算速度提升300%左右，对2000匝线圈计算，时间从原来的2.56小时每状态点，压缩至0.58小时，该快速算法未来超导电工装备电性能计算提供了算法基础。目前该算法理论工作发表在2021年1月份超导技术领域最具影响力的Superconductor Science and Technology期刊上。该算法已经通过http://www.eastfs.com/ ，https://www.htsmodelling.com/ 网站开源，全球有千余次下载，并且转化成为数值仿真教学实验课题http://nusep.phys.tsinghua.edu.cn/。第三、发展了基于BP神经网络PID控制技术的主动抵消式磁场屏蔽系统，研制了宽带、低噪音功率驱动板卡与低延时AD/DA可编程控制器；该系统在1Hz处屏蔽效果最高可达800倍，10Hz处约为100倍，在PID独立控制条件下环境噪音可被压制在0.1nT/Hz^0.5@1Hz尺度以下，已经可以满足市面上各种类型弱磁探头的测试条件，已经初步具备在全开放条件下的生物磁测量条件。与生物磁测量结合特别是开放环境条件下的心磁测量是项目团队下一步重点工作。项目总计发表SCI文章5篇。受邀报告3次，项目总计授权专利1项，培养硕士研究生2人。关于开放式磁场屏蔽以及超导体磁通穿透快速算法的研究成果被清华大学物理系公众号以重要科研进展推送报道。