Witricity shows a resonant system that could charge your phone while it’s in your pocket – but is it green?
A wireless power system could remove the need for chargers and disposable batteries, according to its inventors.
Witricity uses electromagnetic induction to charge deliver power to devices without wires – and can operate over distances of around 2m, according to a demonstration at the TEDglobal conference in Oxford.
In the next year and a half there will be clip-on chargers for devices such as iPhones, which would charge the device while it remains in your pocket, when you arrive at a charging zone, according to Eric Giler, chief executive of the firm: “You might never have to think about plugging a cellphone in again.”
The conference saw Giler using a Google G1 phone and an iPhone powered by the system, as well as a conventional TV, all operating over distances of around 2m.
For devices in physical contact with the power source, the effect is well understood, and widely used in devices such as toothbrushes. The Palm Pre uses a wireless charger called the Touchstone.
Contact-based charging without plugs could be extended to many other devices, except for technology wars between the developers. These may be winding down, as industry group the Wireless Power Consortium is slowly gathering new members including Samsung and Duracell. The list of example products include such essentials as electrically-heated slippers.
Charging devices over a distance has been more difficult because electromagnetic waves would interfere with people or other things in their path. Witricity avoids this problem by switching the signal to a very low frequency.
The low frequencies used by WiTricity have a long wavelength, around 30m, and the transmission operates within the “near-field” region, where magnetic fields predominate over electrical ones, and there is less effect on people. The system, developed by physicist Marin Soljacic at the Massachusetts Institute of Technology (MIT), uses resonance to make sure as much energy as possible is sucked into the destination system.
Apart from the convenience of doing away with wires, the system’s credentials as a power delivery are mixed. The 2007 experiment it is based on had an efficiency of only around 45 percent, but Giler promised power delivered wirelessly would start out 15 percent more expensive than wires, and improve on that.
However, if it replaces disposable batteries, it might have a good impact on the environment. “There are something like 40 billion disposable batteries built every year for power that, generally speaking, are used within a few inches or feet of where there is very inexpensive power,” said Giler in a BBC interview. “It’s the most expensive form of electricity ever invented, at £200 to £300 per Kilowatt-hour.