Superconducting Magnetic Shield for MEG Coupled with Permalloy PC

Abstract

The Biomagnetism measurement is required shielding effect 1/S≦1/10^-7 for using SQUID magnetometer. The superconducting shield is possible to realize ideal low magnetic noise space. But it is required to attenuate every external field inside hollow superconducting cylinder equally. Especially, radial external field decreases gently comparison to axial field. At this time the length of cylinder needs 4.4 m for diameter 1 m to realize shielding effect 1/S≦1/10^-7. On the other hand, it is only 2.1 m for axial field. For that reason, we devised two methods to attenuate radial field rapidly coupled with permalloy.