Experimental correction of the axial shielding equation

Summary form only given. Analytical descriptions of axial shielding for cylindrical shields (neglecting the effect of the openings or caps) is based on the assumption that the field reduction inside the shield is due to the demagnetizing field within the equivalent ellipsoid: S/sub ax/ = 1 + N/sub ell/ /spl mu//sub av/ = 1 + 4 N/sub ell/ /spl mu/t/D ( equation 1), where S/sub ax/ is the axial shielding factor, N/sub ell/ is the demagnetizing factor of the equivalent ellipsoid, /spl mu//sub av/ is the average permeability of the shield (the permeability that is averaged over the shield´s cross-sectional area, /spl mu//sub av/ = 4/spl mu/t/D), /spl mu/ is the permeability and t/D is the thickness-to-diameter ratio of the shield. Equation (1) shows some discrepancy; it seems more reasonable to replace the N/sub ell/ in (1) by the demagnetizing factor of the equivalent rod, N/sub rod/, because the shields analyzed have the same outer surface as the rod does. In order to support the above idea experimentally, we built and investigated ten cylindrical shields with L/D ratios from 1 to 8.3. The results obtained show that the employment of the N/sub rod/ in (1) provides much better agreement between the experimental and analytical results.