The ability to charge devices without plugging them in is creeping into our garages, living rooms and even the furniture itself, but most of these systems require close proximity to the power source. The tools to take wireless charging to the next level already exist, though, according to a new paper that outlines how an LCD-like panel could be used to charge several devices simultaneously from a distance of up to 10 meters (33 ft).
Current systems mostly work through induction. The charging panel contains a coil of wire, and as a current flows through that coil, it generates a magnetic field strong enough to induce a similar current in a nearby coil – say, one that's incorporated into a phone, toothbrush or electric car. The problem with these is that the strength of that magnetic field drops off very quickly, meaning the device needs to stay in contact with, or at least very close to, the power source. The upshot is that while there's no need to actually plug in, you're still effectively tethered to the charging source.
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"Our proposed system would be able to automatically and continuously charge any device anywhere within a room, making dead batteries a thing of the past." says David Smith, professor at Duke University and one of the authors of the paper.
The new system would stretch that range by making use of higher microwave frequencies, and focus the waves towards a device in a room by running them through a flat, LCD-like panel. That panel would be made of a metamaterial that already allows experimental Toyota vehicles to communicate with satellites through a flat "antenna" on the roof.
In this case, each cell in that metamaterial could be tuned to manipulate the electromagnetic wave as desired, which can focus the beams of energy from a wall-mounted panel the size of a TV down to something as small as a smartphone, anywhere in the room. The system could be capable of charging multiple devices at once, and work at a distance of up to 10 m, twice the range of the KAIST system. The Cota system comes close, reaching 9 m (30 ft), but since it's based on phased array technology, it's likely too expensive and power-hungry for home use.
Of course, the proposed system comes with its own hurdles. The electromagnetic energy source behind the panel would need to be developed to balance power, cost and efficiency, and the metamaterial would need to be optimized to best focus the beams of energy without creating secondary "ghost" signals. And while the beams are considered safe for human exposure, the system will still need to turn itself off if someone walks between the panel and the device. But, the team says, these problems aren't dealbreakers.
"All of these issues are possible to overcome — they aren't roadblocks," says Smith. "We actually came up with some nice analytical formulas for coverage areas and efficiencies that would be possible. I think building a system like this, which could be embedded in the ceiling and wirelessly charge everything in a room, is a very feasible scheme. Moreover, there are versions of the concept that can deliver larger power over much larger distances."
The research is published online at arXiv.