基于Halbach结构的低场核磁共振主磁体的设计与实现

Design and implementation of low-field NMR main magnet based on Halbach structure

随着核磁共振不断向便携性和低成本方向发展,核磁共振仪中主磁体的小型化成为了大家关注的重点。为实现核磁共振的小型化,对基于Halbach结构的低场核磁共振主磁体进行了设计与实现。首先,利用ANSYS有限元仿真软件对采用多磁条特定排列形成的Halbach结构进行仿真,对磁条的数量、大小、长度、位置等参数进行调整;其次,根据仿真确定的理想模型参数,实现了主磁体,其为直径108 mm、高170 mm的圆柱体,重4.5 kg,并对其中心磁感应强度和均匀度进行了检测;最后,根据检测结果,设计了一种匀场片矩阵,采用被动匀场的方式将磁体中心5 mm直径球形区域内的均匀度提升至451.68 ppm,中心磁感应强度为221.4 mT。设计中,较好的权衡了磁体性能和生产成本。

As the nuclear magnetic resonance(NMR) continues to develop towards the direction of portability and low cost,the miniaturization of the main magnet in the NMR has become a major concern.To realize the miniaturization of NMR,a low-field NMR main magnet based on Halbach structure is designed and implemented.Firstly,the ANSYS finite element simulation software is used to simulate the Halbach structure formed by the specific arrangement of multiple magnetic stripes to adjust the parameters,such as the number,size,length,and position of the magnetic stripes.Secondly,according to the ideal model parameters determined by the simulation,the main magnet,which is a cylinder of 108 mm diameter and 170 mm height weighing 4.5 kg,is realized and its central magnetic induction strength and uniformity are tested.Finally,based on the test results,a uniform field sheet matrix is designed to improve the uniformity in the 5 mm diameter spherical region at the center of the magnet to 451.68 ppm with a central magnetic induction of 221.4 mT using passive uniformity.In the design,it is a good trade-off between magnet performance and production cost.