How wireless electricity works

How wireless electricity works

The technology under WiTricity’s hood could fill several books, all of which would require advanced degrees to comprehend, but a simple analogy might be an opera singer, facing a table of glasses filled with different amounts of liquid. If she belts out a sufficiently loud note at a single frequency, it might be able to shatter one of those glasses — but only the one whose contents have the corresponding frequency. All of the other glasses — and everything else in the room, for that matter — would be unscathed.
In the MIT experiment, two copper coils were set up — one a "sender" and one a "receiver." The sender coil was attached to the power source, while the receiver coil was attached to the light bulb. When turned on, the sender coil emits electricity in the form of a magnetic field, oscillating at a specific frequency. The receiver coil picks up the transmission, while the rest of the environment is unaffected. One specific opera singer, sending energy to one specific wine glass.
Strictly speaking, wireless transfer of power is not new — electromagnetic induction, the process that takes place when you set your cordless phone in its charger base, is technically wireless, although it requires extremely close proximity. And scientists are still arguing about the merits of Nikolai Tesla’s work in Colorado Springs at the turn of the 19th century, when he built his eponymous coils that sent power not only through the air but the ground.
The MIT team said its discovery is different from all previous efforts because it uses "magnetically coupled resonance," which means it will not only be safe, but it will be fairly efficient.
"In order for the power transfer to be efficient, we design the system such that the rate of energy transfer between the emitter and the receiver is greater than the rate of energy dissipation," Kurs said. "This way, the device can ‘capture’ the energy and use it for useful work before too much of it gets wasted away."
The other major breakthrough here is the nature of the power’s delivery — in a word, it is omni-directional. Tesla coils and cordless phone chargers require precise positioning of both ends of the delivery chain; WiTricity imagines a world in which the power is in the air, and can be snagged by any device that needs it.
"As long as (a laptop) is in a room equipped with a source of such wireless power, it would charge automatically without having to be plugged in," writes Prof. Peter Fisher in a white paper on the experiment. "In fact, it would not even need a battery to operate inside of such a room."

Is it practical — and is it safe?

The WiTricity demonstration is still too recent, and too focused, to produce any definitive conclusions — a 60W light bulb is very different from a plasma screen, after all. Kurs said his team has been focused on smaller transfers of power, but he said it will be possible to power a digital display wirelessly — he just can’t say when, exactly.
"With the WiTricity method, they anticipate transmitting power over distances of about a meter, which is much less than ideal but still very impressive," said electrical engineer Charles Lidstone. "I wonder what level of wirelessness represents the best trade-off between convenience, efficiency, safety, cost and whatever else you can think of. In the end, its usefulness will depend on how well implemented a future product is, I think."
If the technology is improved and honed to a point where it can be "product-ized," it stands to turn any number of industries on their respective ears. Digital signage and retail technology in general will undoubtedly be some of the first in line, as power cables are the bane of many an installation.
"(Wiring issues are) a big impediment to development in the retail sector right now, because most stores have aisles and aisles of shelves with no power in them," said Dave Haynes of the digital signage company Digital View. "The only solution, in most cases, is dropping wire down from the ceiling and that generally looks like crap."
Wireless power would also make it possible for deployers to pull off creative installations, such as in the middle of a shopping mall. "Understandably, mall and high-end building operators are not real wild about cutting trenches into their marble floors to get power to a display planned for the middle of a walkway," Haynes said.
Gerba said such a technology, if it were reliable and safe, would not only reduce installation and maintenance costs, it would make possible some installation ideas that have been merely dreams up to this point — like placing small screens in close proximity to certain products on shelves, then moving the screens around as needed.
So, what about safety? To most, the idea of electricity swirling through the air is unsettling at best, downright terrifying at worst.
"I am fairly certain I would be loath to spend much time around a wireless power transmitter," Haynes said. "I get all these weird, Stephen King ideas about AV installers turning into Magnetic Men superheroes."
But the MIT team points out that magnetic fields interact very weakly with most common materials, and extremely weakly with biological materials (i.e. people and animals). Everybody hears the opera singer’s voice, but only the intended recipients can convert it into power.
"Unlike Tesla coils, our scheme does not rely on high electric fields," Kurs said. "The safety issue certainly needs to be explored further very carefully, but our calculations indicate that it is possible to design a wireless power transfer system that operates within the IEEE’s safety guidelines."