Charts for estimating the axial shielding factors for triple-shell open-ended cylindrical shields

Describing the shields with the number of shells greater than two differs from the previously done work in having a significant increase in the number of charts needed. To limit the number of charts, only the shields were examined that have the most-used exterior aspect ratio, namely, equal to 5. It was also assumed that all the shielding shells are made of the same material with an equal and relatively small thickness, which is a practical case as well. Since the three-shell structure does not allow much freedom for variations in the air gaps between the shells, only the shields having air gaps of 5% and 10% of the diameter of the outermost shell were considered. Finally, a set of charts was computed with the help of a standard ANSYS® software employing an FEM method. The charts are represented as logarithmic contour plots where the ratio of the inner to outer shells' lengths and permeability normalized to the thickness-to-diameter ratio of the outermost shell are independent variables; and the air gaps and ratio of the middle to outer shells' lengths are fixed parameters. The charts calculated allow one to quickly estimate the axial shielding factor and to clearly observe the effect of the shield's parameters on the axial shielding.