Abstract
We developed a human-size, open-structure, vertical cylindrical magnetic shield consisting of four shells. The inside diameters of the four shells are 0.67 m, 0.72 m, 0.82 m and 0.97 m, respectively. The lengths of the shells are 1.80 m, 2.20 m, 2.43 m and 2.75 m, respectively. The first shell is made of Permalloy (2.1 mm thick). Other three shells, made of amorphous ribbons (approximately 50 mm wide, approximately 22 μm thick), employ magnetic shaking. The second shell consists of four subdivided helical shells with internal space of about 10 mm. Each subdivided helical shell comprises of 12 layers, with the amorphous ribbons wound helically. The outer two shells have an axial structure, in which the ribbons are placed along the axial direction of the cylinder. The third shell has 26 layers and the fourth shell has 30 layers of the amorphous ribbons. The shielding factor measured at the center was approximately 100,000 for the transverse magnetic field and approximately 380 for the axial magnetic field, the amplitude of the magnetic field being in both cases 10,000 nT. The leakage field from the shaking coils at the center of the shield was below 1 nT permitting operation of highly sensitive SQUID magnetometers.
