Development of a large-scale vertical setting cylindrical magnetic shield - Realization of low-level, low-gradient magnetic field with current superposition

大型立式圆筒磁屏蔽研制——电流叠加实现低水平低梯度磁场

基本信息

批准号：
09555129
负责人：
SASADA Ichiro
金额：
$ 7.87万
依托单位：
KYUSHU UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1997
资助国家：
日本
起止时间：
1997 至 1998
项目状态：
已结题

项目摘要

(1) We designed a large-scale vertical open-structure cylindrical magnetic shield and constructed it employing magnetic shaking. The shield developed consists of four concentric magnetic shells positioned on the outer surfaces of paper pipes of 〜 270 cm length, 〜 1 cm thickness, and with outer diameters of 67, 72, 82, and 97 cm, respectively. The first (innermost) shell is a passive Permalloy shell of 2.1 mm thickness and 180 cm length. The second, third and fourth shells are made of 〜 5 cm wide and 〜 22 μm thick Metglas 2705M amorphous ribbons. The second shell is a 220 cm long helical structure of 48 layers of the amorphous ribbons. The third shell, 243 cm in length and fourth shell, 270 cm in length, are axial structure consisting of 26 and 30 layers, respectively. The gross weight of the sheild is 〜 400 kg including 〜 68 kg of Permalloy and 〜 110 kg of Metglas ribbons. An 〜 10ィイD15ィエD1 transverse shielding factor and a relatively large 〜 380 axial shielding factor, despite of the e … More ffect of openings, are achieved for a 10 μT external magnetic field in the extremely low frequency region. The shaking leakage measured by a fluxgate at the shield's center is less than 1 nT and the level of magnetic noise field measured by a SQUID magnetometer at the same position is less than 1 pT.(2) The optimum geometry of the open-ended cylindrical magnetic shield is presented for the maximum axial shielding factor and for the maximally flat distribution of the magnetic field inside the shield. With the geometrical parameter including the diameter, D, the length, L, and the thickness, t, and with the material parameter, the permeability μ, a maximum shielding factor for the axial magnetic field is obtained when L/D = 1 + log (μt/D), and a maximally flat distribution is obtained when L/D = 1 + log (μt/D) + C where C = 0.75 〜 1.0.(3) The effect of magnetic anisotropy on the shaking enhancement is made clear. The magnetic field to be shielded should be parallel to the easy axis of magnetization, whereas shaking magnetic field does not have such preference in direction. However, the amplitude of the shaking magnetic field required is ten times larger when the shaking magnetic field is applied perpendicularly to the easy axis than that required when applied in parallel. Less

(1) 我们设计了一个大型垂直开放式结构的圆柱形磁屏蔽，并利用磁振动构建了它。该屏蔽由四个同心磁壳组成，位于长约 270 厘米、厚约 1 厘米的纸管外表面上。，外径分别为 67、72、82 和 97 厘米。第一个（最内）壳是厚度为 2.1 毫米的被动坡莫合金壳。第二个、第三个和第四个壳长 180 厘米，由约 5 厘米宽和约 22 微米厚的 Metglas 2705M 非晶带制成。第二个壳是 220 厘米长的螺旋结构，由 48 层非晶带组成。第2壳长243厘米，第4壳长270厘米，分别为26层和30层的轴向结构。屏蔽的重量约为 400 千克，包括约 68 千克的坡莫合金和约 110 千克的金属玻璃带，在极低频区域中实现了 10 μT 的外部磁场。屏蔽中心小于1 nT，SQUID磁力计在同一位置测量的磁噪声场水平小于1 pT。(2)针对最大轴向磁屏蔽，提出了开放式圆柱形磁屏蔽的最佳几何形状。屏蔽系数和屏蔽内部磁场的最大平坦分布，几何参数包括直径 D、长度 L 和厚度 t，以及材料参数磁导率 μ，当 L/D = 1 + log (μt/D) 时，获得轴向磁场的最大屏蔽系数；当 L/D = 1 + log (μt/D) + C 时，获得最大平坦分布，其中 C = 0.75～1.0。(3)明确了磁各向异性对振动增强的影响，要求屏蔽的磁场应平行于易磁化轴，而振动磁场在方向上没有这种偏好。然而，垂直于易磁化轴施加振动磁场时所需的振动磁场的振幅比平行施加时所需的振动磁场的振幅大十倍以下。