Two-Dimensional Coil System Compensating X, Y, Z-Components of Leakage Field from an Aperture of Magnetic Shields and its Application to a Large-Scale Cylindrical Shield

提出了一种通过磁屏蔽开口处的磁场进行补偿的新方法。该方法以地磁场和交变磁场为外磁场进行补偿。采用端部开孔的坡莫合金圆柱壳(外径68 cm，长180 cm)和外表面螺旋缠绕16层的Metglas 2705M非晶薄带，研制了大型圆柱形屏蔽壳。磁振动场只施加在非晶层上，通过36圈的环形振荡圈。圆柱形屏蔽盒被放置在地板上，其轴线垂直于地球磁场的方向。在屏蔽罩的中心区域，地球磁场被衰减到0.1毫克(10nT)以下。残余磁场呈圆柱形，分布较为平坦。地磁场的水平分量(0.32G)和垂直分量(0.35G)在圆柱形屏蔽体的开口端使用由对应于每个分量的反馈系统控制的平八字形线圈(直径74厘米)进行补偿。剩余磁场小于0.15毫克的有效屏蔽区向开口端延伸约30厘米(大约半径)。地磁场水平分量的补偿电流为2.3A圈。通过采用最新开发的补偿技术，成功地构建了一种轻质、高性能、低成本的人体尺寸的磁屏蔽样机

A new method was developed by which magnetic fields coming in through an opening of a magnetic shield can be compensated. The earth's magnetic field and ac magnetic field were targeted as external magnetic fields to be compensated by the method. A large-scale cylindrical shielding case was developed for this study using a Permalloy cylindrical case (outer diameter =68cm, length=180cm) with an opening at an end and Metglas 2705M amorphous ribbons, which were wound helically on the outer surface of the Permalloy case by 16 layrs. Magnetic shaking field was applied to only the amorphous layrs by a toroidal shaking coil of 36-turns. The cylindrical shielding case was laid on the floor with its axis perpendicular to the direction of the earth's magnetic field. The earth's magnetic field was attenuated to below 0.1 mG (10 nT) at the central region of the shield. The distribution of residual magnetic field was nearly flat due to the cylindrical shape. The horizontal component of the earth's field (0.32 G) as well as vertical one (0.35 G) was compensated at the open end of the cylindrical shield using a flat figure-eight coil (74 cm in diameter) controlled by a feedback system corresponding to each component. Effectively shielded area where residual magnetic field was less than 0.15 mG was extended by about 30 cm (approximately by a radius) toward the open end. Compensating current for the horizontal component of the earth's field was 2.3 A-turn. Magnetic field applied axially by a large square coil was also compensated using a ring coil of the same diameter.By incorporating a newly developed compensating technique we successfully constructed a prototype magnetic shield of human size which is light-weight, high-performance and low-cost