A Figure of Merit for the Design of Inductance Coils Having Low Distributed Capacitance

The performance of an inductor is often significantly compromised by the combined effects of series resistance and distributed capacitance. For a given inductance value and coil configuration, it is always possible to vary the absolute size and/or turns count so as to reduce one residual parameter at the expense of an increase in the other. The ratio M = L/RC²is unaffected by these transformations and is proposed as a figure of merit characterizing the particular coil design. Measurements of M for sample coils of a number of commonly used types are given; they provide lower limits to the performance attainable with available magnetic materials.