A new type of magnetic shield (abstract)

Abstract

We propose a new type of magnetic shield which is made by piling the many U-shaped soft magnetic materials. We call it ♯-type shield because of its shape as shown in Fig. 1. The principle of magnetic shielding is based on the zero vector sum of the applied field and demagnetizing field outside the soft magnetic specimens. In this way a weak field region is produced inside the ♯-type shield which screen out the external field. Therefore, shielding effectiveness can be controlled by changing the demagnetizing factor which primarily depends on the shape of the specimen. It is hard for the conventional magnetic shield like a cylindrical shell to control its demagnetizing factor, therefore, the shielding effectiveness is based on only the permeability of the soft magnetic materials. However, it is easy for the ♯-type shield to control its demagnetizing factor by changing the length of U-shaped speciments. The shielding ratios S (external field/internal field) of the ♯-type shield have the maximum as the external field increases. The demagnetizing field due to U-shaped iron cancels perfectly the external field when the shielding ratio S is maximum. Therefore, S is extremely high (S=104). The critical field at which S is maximum optionally varies with the length L of U-shaped specimens. The shielding effectiveness of ♯-type shield using iron is as effective as that of the cylindrical shield using permalloy. The ♯-type shield is more economical. The shield is free from temperature rising because of the open structure. The ♯-type shield using iron can be applied to almost any device having magnetic structure or involving electron beam.