Shielding of longitudinal magnetic fields with thin, closely, spaced concentric cylindrical shells with applications to atomic clocks

A general formula is given for the longitudinal shielding effectiveness of N closed concentric cylinders. The use of these equations is demonstrated by application to the design of magnetic shields for hydrogen maser atomic clocks. Examples of design tradeoffs such as size, weight, and material thickness are discussed. Experimental results on three sets of shields fabricated by three manufacturers are presented. Two of the sets were designed employing the techniques described. Agreement between the experimental results and the design calculations is then demonstrated.