Study of a Leakage Magnetic Field due to an Opening in a Multi-layer-type Magnetically Shielded Room using Finite Element Method

Abstract

A typical magnetically shielded room (MSR) for an electron beam lithography system and biomagnetic measurements is composed by multi-layered ferromagnetic materials such as μ-metal. However, a number of openings must be provided in the wall and floor for air conditioning and cables. In this paper, the optimal structure of a duct to prevent leakage flux from entering through the openings was investigated by 3-D magnetic field analysis. We found that the duct should be connected to the inner layer in order to reduce the introduction of the leakage fluxes from the middle and outer layers. When magnetic noise is applied vertically to the opening, the duct protruding from the outer layer should be short, in order to avoid gathering surplus fluxes from outside the MSR. Inner partition plates dividing the hole of the duct are also effective for this purpose.