Superconducting magnetic shields for SQUID applications

Abstract

We investigate the shielding of superconducting and μ-metal forms in axial and transverse directed background magnetic noise fields. Analytical expressions are obtained for the improvement in signal-to-noise ratio obtained by placing a superconducting disk in the presence of a dipole source and a uniform noise field. Axial and transverse shielding factors are then compared for identical superconducting and μ-metal cylinders. The signal-to-noise ratio is found to be infinite at certain points inside a superconducting cylinder as well as a superconducting cylinder with a central partition. Shielding factors obtained here are relevant to SQUID measurements of small dipole source fields in the presence of large background noise fields such as those encountered in biomagnetism and nondestructive evaluation.