Capacitance of Disk Capacitors

The capacitance of a parallel plate capacitor is formulated in basic electrostatics, assuming that the separation between the two electrode plates is very narrow and the fringe field of the edges is negligible. However, in practical problems of electrical and electronic engineering there are many cases where the plate separation is wide and the fringe field effect cannot be neglected. In our previously published paper the capacitance of strip capacitor was computed by the boundary element method (BEM) for the case where the separation becomes wide, and a new empirical formula of the capacitance against the plate separation was derived. The empirical formula agreed well with experimental data. This paper presents a “formula” for the capacitance of a parallel plate disk capacitor. The “formula” is valid over a wider separation than formulas presented previously. As a special case of the problem, the capacitance of parallel plate ring capacitors is computed by the BEM.