Resonant inductive coupling or
electrodynamic induction is the
near field wireless transmission of electrical energy between two magnetically coupled coils that are part of
resonant circuits tuned to
resonate at the same frequency. This process occurs in a
resonant transformer, an electrical component which consists of two high
Q coils wound on the same core with
capacitors connected across the windings to make two coupled
LC circuits. Resonant transformers are widely used in
radio circuits as
bandpass filters, and in switching power supplies. Resonant inductive coupling is also being used in
wireless power systems. Here the two
LC circuits are in different devices; a transmitter coil in one device transmits electric power across an intervening space to a resonant receiver coil in another device. This technology is being developed for powering and charging portable devices such as cellphones and tablet computers at a distance, without being tethered to an outlet.