Shielding Factor and Maximum Magnetic Flux Density of Cylindrical Magnetic Shield against Axial Magnetic Field

Abstract

Studies on the shielding factor against the transverse magnetic field have been carried out but that against the axial (longitudinal) magnetic field is less studied. Moreover, the maximum magnetic flux density in magnetic materials of the shield is not evaluated up to the present.Applying existing approximate expressions for the shielding factor, approximate expressions for the maximum magnetic flux density were derived for single and double cylindrical magnetic shields. In order to evaluate the accuracy of the expressions, the linear finite element method (FEM) was used to calculate the shielding characteristics of shields with different length and thickness. The calculated results by both the FEM and the approximation agreed considerably in the case of the single cylinder but the agreement was obtained only within the limited shield dimensions for the double cylinder.