The aluminum shielded room has been an important part of ultra-low-field magnetic resonance imaging （ULF MRI） based on the superconducting quantum interference device （SQUID）. The shielded room is effective to att...The aluminum shielded room has been an important part of ultra-low-field magnetic resonance imaging （ULF MRI） based on the superconducting quantum interference device （SQUID）. The shielded room is effective to attenuate the external radio-frequency field and keep the extremely sensitive detector, SQUID, working properly. A high-performance shielded room can increase the signal-to-noise ratio （SNR） and improve image quality. In this study, a circular coil with a diameter of 50 cm and a square coil with a side length of 2.0 m was used to simulate the magnetic fields from the nearby electric apparatuses and the distant environmental noise sources. The shielding effectivenesses （SE） of the shielded room with different thicknesses of aluminum sheets were calculated and simulated. A room using 6-mm-thick aluminum plates with a dimension of 1.5 m x 1.5 m x 2.0 m was then constructed. The SE was experimentally measured by using three-axis SQUID magnetometers, with tranisent magnetic field induced in the aluminum plates by the strong pre-polarization pulses. The results of the measured SE agreed with that from the simulation. In addition, the introduction of a 0.5-mm gap caused the obvious reduction of SE indicating the importance of door design. The nuclear magnetic resonance （NMR） signals of water at 5.9 kHz were measured in free space and in a shielded room, and the SNR was improved from 3 to 15. The simulation and experimental results will help us design an aluminum shielded room which satisfies the requirements for future ULF human brain imaging. Finally, the cancellation technique of the transient eddy current was tried, the simulation of the cancellation technique will lead us to finding an appropriate way to suppress the eddy current fields.展开更多
无铁芯超导直线同步电机(superconducting linear synchronous motor,SLSM)具有推力密度高、工作气隙大等优势,是超导磁浮列车的动力核心。由于会不可避免地受到弯道、道岔、横风和电源谐波等因素的影响,磁浮列车在运行过程中将发生多...无铁芯超导直线同步电机(superconducting linear synchronous motor,SLSM)具有推力密度高、工作气隙大等优势,是超导磁浮列车的动力核心。由于会不可避免地受到弯道、道岔、横风和电源谐波等因素的影响,磁浮列车在运行过程中将发生多自由度运动,使电机次级姿态发生滚转或偏移,致使超导直线电机的电磁力性能发生改变,进而影响列车的运行稳定性。针对多变电机次级姿态下高温超导直线同步电机的三维力特性展开研究,首先分析悬浮车体多自由度运动对直线电机次级姿态的影响,并建立计算SLSM三维电磁力的有限元模型;其次,通过搭建超导同步直线电机样机,实验验证模型的有效性;最后,基于该模型研究无铁芯SLSM次级在发生横向偏移、法向偏移、侧滚、俯仰以及偏航条件下的三维电磁力输出特性及其变化规律,为超导磁浮列车运行性能优化提供了理论依据。展开更多
基金Project supported in part by the Strategic Priority Research Program(B)of the Chinese Academy of Sciences(Grant No.XDB04020200)in part by the National Natural Science Foundation of China(Grant No.11204339)
文摘The aluminum shielded room has been an important part of ultra-low-field magnetic resonance imaging （ULF MRI） based on the superconducting quantum interference device （SQUID）. The shielded room is effective to attenuate the external radio-frequency field and keep the extremely sensitive detector, SQUID, working properly. A high-performance shielded room can increase the signal-to-noise ratio （SNR） and improve image quality. In this study, a circular coil with a diameter of 50 cm and a square coil with a side length of 2.0 m was used to simulate the magnetic fields from the nearby electric apparatuses and the distant environmental noise sources. The shielding effectivenesses （SE） of the shielded room with different thicknesses of aluminum sheets were calculated and simulated. A room using 6-mm-thick aluminum plates with a dimension of 1.5 m x 1.5 m x 2.0 m was then constructed. The SE was experimentally measured by using three-axis SQUID magnetometers, with tranisent magnetic field induced in the aluminum plates by the strong pre-polarization pulses. The results of the measured SE agreed with that from the simulation. In addition, the introduction of a 0.5-mm gap caused the obvious reduction of SE indicating the importance of door design. The nuclear magnetic resonance （NMR） signals of water at 5.9 kHz were measured in free space and in a shielded room, and the SNR was improved from 3 to 15. The simulation and experimental results will help us design an aluminum shielded room which satisfies the requirements for future ULF human brain imaging. Finally, the cancellation technique of the transient eddy current was tried, the simulation of the cancellation technique will lead us to finding an appropriate way to suppress the eddy current fields.
文摘无铁芯超导直线同步电机(superconducting linear synchronous motor,SLSM)具有推力密度高、工作气隙大等优势,是超导磁浮列车的动力核心。由于会不可避免地受到弯道、道岔、横风和电源谐波等因素的影响,磁浮列车在运行过程中将发生多自由度运动,使电机次级姿态发生滚转或偏移,致使超导直线电机的电磁力性能发生改变,进而影响列车的运行稳定性。针对多变电机次级姿态下高温超导直线同步电机的三维力特性展开研究,首先分析悬浮车体多自由度运动对直线电机次级姿态的影响,并建立计算SLSM三维电磁力的有限元模型;其次,通过搭建超导同步直线电机样机,实验验证模型的有效性;最后,基于该模型研究无铁芯SLSM次级在发生横向偏移、法向偏移、侧滚、俯仰以及偏航条件下的三维电磁力输出特性及其变化规律,为超导磁浮列车运行性能优化提供了理论依据。
