Some Possibilities for Low Loss Coils

A toroidal coil wound with a flat conductor so curved that the flat side follows exactly the surface of the toroid has remarkably low losses. The Q (=ωL/R) of such a coil is independent of the number of turns, is proportional to size, and to the square root of frequency. For maximum Q there is a best proportion which is given in the paper for the case of toroids of rectangular and circular cross sections, together with formulas for calculating the losses and the Q for such toroids. These formulas show that values of Q between 1000 and 10,000 are theoretically realizable with reasonable dimensions. The practical difficulties of realizing the theoretical possibilities are discussed, and it is shown that the mechanical construction must have a perfection comparable to the skin depth of current penetration.