A recent YouTube video by Hyperspace Pirate demonstrates the optimised wireless power transfer using inductive coupling, however, it has been noted that there are large losses involved once the distance between the transmitter and receiver is increased.
The transmitter in the video- which has 10kV on the coil, oscillates at 145kHz, and uses a 4.6-metre hexagon with eight turns of 14 AWG wire as its antenna- was able to light an LED at a distance of 40m.
Although the tests show that there are boosting effects for the range usingintermediate (unpowered) coils between the transmitter and receiver, it has been said that this technology is not practical for power transfer over distance.
Modern attempts to charge phones wirelessly do trade efficiency for convenience, and systems such as those by Energous and Ossia use large phased array transmitters and target tracking to help counter the problems with the Friis Transmission Equation, however, the apertures still need to be many wavelengths in size for them to work.
