Abstract :
The paper starts with an outline of Butterworth´s method for the determination of the high-frequency resistance of an isolated single-layer solenoid. It points out that his method must tend to exaggerate the resistance, and accordingly a modification is suggested. By applying the modification, the high-frequency resistance of a particular coil is computed and it is shown that the losses are less than those which would be obtained using Butterworth´s formulae. Comparison is made with Jackson´s measurements, which show that Butterworth´s formulae, in fact, tend to underestimate the resistance, and it is consequently noted that there must be a further underestimation by the method given in the paper. When the coil is surrounded by a concentric screening-can, not only are the losses in the coil altered, but further losses arise in the screening-can itself. Butterworth´s method still applies to the former, and an expression is derived for the latter. This expression is compared with Bogle´s empirical formula and is found to agree very well, provided that the coil is not too short. Finally there is a worked example where a particular screened coil is taken for which all the losses are calculated, and the effect of the screening-can on the Q-factor of the coil is determined.
