An Oudin coil, Oudin oscillator, Oudin resonator, or Oudin Configuration is a modified Tesla Coil for producing high voltage arcs and discharges. Though an autotransformer in appearance, like all Tesla Coils it is a resonant transformer with primary and secondary circuits tuned to the same frequency. It is powered by a neon sign or other suitable high voltage transformer, and oscillation is maintained in its primary circuit by the negative resistance of a spark gap. The Oudin configuration is disfavored by Tesla Coil builders as being an unnecessary distraction which provides no performance improvement while exposing operators to potentially lethal currents at its secondary terminal. Nonetheless in 1889 Paul Marie Oudin (1851–1923), a French Physician and experimenter and Jacques d'Arsonval were granted a patent for their configuration, nine years after the work of Tesla.