An AC power source applies power to a primary coil that is provided in a fixed part. An AC current flowing through the primary coil induces electromotive force in a secondary coil that is provided in a movable part. The AC electromotive force induced in the secondary coil is converted by an AC/DC converter...http://www.google.fr/patents/US6556165?utm_source=gb-gplus-shareBrevet US6556165 - Antenna apparatus and waveguide rotary coupler
