English: A block diagram of a wireless power system using resonant inductive coupling. Resonant inductive coupling is the transmission of electric power using magnetic fields between two resonant circuits, one in a transmitting device and one in a receiving device. This technology, invented by Nikola Tesla in the 1890s but further developed and popularized by a team led by Marin Soljačić at MIT in 2007, allows high efficiency wireless transmission of power at ranges of 4 to 10 times the coil diameter, much farther than nonresonant inductive coupling. In 2007 Soljačić's team achieved transmission of 60 watts of power over a distance of 2 meters at about 40% efficiency. This block diagram shows the system they used. The two resonant circuits were self-resonant coils of wire with internal capacitance (dotted capacitors). Both are tuned to the same resonant frequency. In the transmitter an electronic oscillator generates a high frequency oscillating current through the small lefthand coupling coil. This induces an oscillating current in the lefthand resonant circuit. The lefthand resonant circuit creates a magnetic field (B, green) that induces an oscillating current in the righthand resonant circuit. This power is coupled out of the resonant circuit by the small righthand coil, and rectified to direct current to power the load.