Technology[edit]
WiTricity is based on strong coupling between electromagnetic resonant objects to transfer energy wirelessly between them. This differs from other methods like simple induction, microwaves, or air ionization. The system consists of transmitters and receivers that contain magnetic loop antennas critically tuned to the same frequency.[citation needed]
Because WiTricity devices operate in the electromagnetic near field, receiving devices must be no more than about a quarter wavelength from the transmitter. In the system demonstrated in the 2007 paper, this was only a few meters at the frequency chosen. In their first paper, the group also simulated GHz dielectric resonators. WiTricity devices are coupled almost entirely with magnetic fields (the electric fields are largely confined within capacitors inside the devices), which they argue makes them safer than resonant energy transfer using electric fields (most famously in Tesla coils, whose high electric fields can generate lightning), since most materials couple weakly to magnetic fields.[9]
Unlike the far field wireless power transmission systems based on traveling electro-magnetic waves, WiTricity employs near field resonant inductive coupling through magnetic fields similar to those found in transformers, except that the primary coil and secondary winding are physically separated, and tuned to resonate to increase their magnetic coupling. These tuned magnetic fields generated by the primary coil can be arranged to interact vigorously with matched secondary windings in distant equipment but far more weakly with any surrounding objects or materials such as radio signals or biological tissue.[citation needed]
In particular, WiTricity is based on using 'strongly-coupled' resonances to achieve a high power-transmission efficiency. Aristeidis Karalis, referring to the team's experimental demonstration, says that "the usual non-resonant magnetic induction would be almost 1 million times less efficient in this particular system".[2] The researchers suggest that exposure levels are below the threshold for FCC safety regulations, and the radiated-power levels comply with FCC radio interference regulations.
Researchers attribute the delay in developing wireless-power technology to limitations of well-known physical laws and a simple lack of need. Only recently have modern consumers obtained a high number of portable electronic devices that use batteries and plug-in chargers.[2]