2014 Articles

Paul Drude’s Prediction of Nonreciprocal Mutual Inductance for Tesla Transformers

McGuyer, Bart H.

Inductors, transmission lines, and Tesla transformers have been modeled with
lumped-element equivalent circuits for over a century. In a well-known paper from
1904, Paul Drude predicts that the mutual inductance for an unloaded Tesla
transformer should be nonreciprocal. This historical curiosity is mostly forgotten
today, perhaps because it appears incorrect. However, Drude’s prediction is shown
to be correct for the conditions treated, demonstrating the importance of constraints
in deriving equivalent circuits for distributed systems. The predicted nonreciprocity
is not fundamental, but instead is an artifact of the misrepresentation of energy by
an equivalent circuit. The application to modern equivalent circuits is discussed.