A new wirless power transmission system uses receivers that are only about a foot across – moving closer to a size that could eventually be built into a PC or a television set. The transmitting coil could be built into a wall or ceiling, the researchers say, and the transfer of power has been shown to work over distances comparable to the size of an ordinary room.
Although predicted by theory, the increase in efficiency when powering two devices at the same time had not been previously demonstrated in experiments. The team that carried out the recent work — Kurs, Moffat and Soljačić — found that when powering two devices at once, which individually could achieve less than 20 percent efficiency in power transfer, the combined efficiency climbed to more than 30 percent. The two receiving coils resonate with each other as well as with the transmitting coil, and help to reinforce the strength of the magnetic field. Kurs says that the efficiency should continue to rise as more devices are added, climbing toward a theoretical limit of 100 percent