Content for id "text" Goes Here

Recharge Station

New technology that allows for wireless charging of electronic devices could make a rarity of cord jungles like the one in this image, captured this year at a power generation station in New York City during the blackout caused by Hurricane Sandy.

Photograph by Timothy A. Clary, AFP/Getty Images


Wireless Energy

Will Ferguson in Boston
For National Geographic News
Published December 28, 2012

A mobile phone that charges in your pocket, a flat-screen TV that needs no power cord, a car fueled by a cordless panel in the floor: In a nondescript building just outside Boston, these and other applications of wireless electricity signal a future with fewer snaking cables.

WiTricity, a company spun off from research at the Massachusetts Institute of Technology (MIT), aims to redefine how people use energy, making it possible to power devices without ever plugging them into an outlet. In WiTricity's lab, various devices run on power transmitted via electric coils through the air.

Plugged In, Virtually

"It is not hard to imagine that in the next few years, you go to a coffee shop, sit down in a chair, sign into a power zone, and charge your phone or laptop," said Richard Martin, editorial director for Pike, a market research group that focuses on smart-energy solutions. "We predict this technology taking off in a similar fashion to how Wi-Fi got its start a decade or so ago."

Martin says the industrial potential for wireless power is huge, especially in the realm of electric vehicles and wireless sensors, where harsh environments make it difficult to run wiring. In addition, he says wire-free electricity transmission is often a more convenient, greener alternative to conventional plug-in charging. (See related blog post: "Wireless Power Can't Yet Replace Utility Poles, but Could Offer More Options for Electronic Charging") "Part of this is that there is an obviously big space in the market waiting to be filled," Martin said.

WiTricity CEO Eric Giler imagines a future where power devices are embedded in the walls and carpets of homes, making for a truly wire-free household. He says with a big enough power supply and small wireless repeaters, one could even power a grocery store or office building.

Conventional charging devices such as the cord for a cell phone use electromagnetic induction to transmit power. Through electromagnetic induction, an electric current is sent through a magnetic field generated by a power conductor to a smaller magnetic field generated by a receiving device. (See related quiz: "What You Don't Know About Electricity")

"Think of your electric toothbrush," Giler says. "It works very efficiently, but the problem is that it can only transmit power wirelessly a few inches."

WiTricity devices share energy through magnetic fields as well. However, unlike those generated by your toothbrush or iPod cable, WiTricity's devices produce magnetic fields through a process called resonant magnetic coupling, which allows power to be transmitted several meters in distance.

Resonant coupling is a well-understood concept illustrated by many everyday examples. A child pumps her legs at the resonant frequency of a swing to fly through the air, or an opera singer shatters a wine glass by singing a single note at a frequency that matches the acoustic resonance of the glass.

WiTricity founder and MIT professor of physics Marin Soljačić wondered whether electricity could be passed from a wall outlet to an electronic device in a similar manner after he was awoken late one night in 2007 by the beeping of his wife's dying cellphone.

He experimented with two electromagnetic resonators vibrating at a specific frequency and found they shared power through their magnetic fields at distances far greater than their conventional, magnetic induction counterparts. The results of his work were published in the journal Science later that year, and WiTricity was founded soon after to develop the technology for commercial use.

Hope for the Electric Car Market?

Giler says materials such as wood, brick, and concrete are essentially transparent to magnetic fields, enabling two WiTricity devices to transfer power through them in amounts ranging from a few milliwatts to several kilowatts.

As the number of household electronic devices proliferates, so do concerns about electromagnetic radiation exposure from these devices and the possible health effects. Giler, however, says WiTricity's technology is safe. While the human body responds strongly to electric fields, (the same response that makes it possible to cook the meat of a chicken or steak in a microwave), Giler says humans do not absorb power from the low-level, magnetic field generated by a WiTricity device.

"If you are OK living on Earth, then you should be OK with what we are doing at WiTricity," he says. "Our technology generates less radiation than the Earth's magnetic field; it is one hundred times safer than a cell phone and generates a million times less radiation than an MRI machine."

He says WiTricity is developing wirelessly powered devices ranging from an iPhone to implanted medical devices and military robots. Both Giler and Martin agree that the electric-vehicle industry will be the first market sector to benefit from wireless power transmission.

"The electric-car industry has figured out that people aren't going to use electric vehicles if they have to constantly plug them in," Giler says. "We are trying to make charging your car as convenient as fueling it at the pump."

In the bumper of an electric BMW coupe, WiTricity has placed a wireless coil that receives power from a resonator embedded in the floor beneath the car. The system can transmit up to 3,300 watts per hour and takes four to six hours to fully charge the vehicle.

A market report recently released by Pike predicts wireless charging systems will make a big difference for the sluggish electric vehicle market worldwide, helping to increase EV sales from 120,000 in 2012 to more than 280,000 by the end of the decade. Martin says this is primarily due to big investments in the technology on the part of major EV manufacturers. He predicts that as the systems become prevalent in towns and cities, the added convenience of not having to plug in will make buying an EV a more palatable option for convenience-minded consumers. (Related blog post: "How to Compare the Cost of Electric and Gas Cars")

Martin says wireless power is currently being used both in the United States and abroad in experimental vehicle systems. In South Korea, researchers are using power pads on a prototype bus route to feed energy to transport vehicles. At Google headquarters in California, wireless power is being offered free of charge to employees who choose to go electric.

In Europe, wireless-energy developer Qualcomm recently kicked off a two-year project with Renault to test the feasibility of embedding wireless power in the roadway. Called Halo, the technology involves inductive coils placed both in the road and on the underbelly of a vehicle. When a car drives over segments of roadway with the inductive coils, it will receive an energy boost.

While tearing up roadways for electric-powered driving would be a multibillion-dollar project decades down the line, Martin says to expect dynamic charging stations at stoplights and landing pads on bus routes in the not-too-distant future.

"It is really not that hard to envision," Martin says. "Similar to a wireless Internet provider, you will be signed up with a particular service, and the system will charge you automatically when you download power from an overhanging station or pad in the roadway." (See related photos: "Five Most Hopeful Energy Stories of 2012")

This story is part of a special series that explores energy issues. For more, visit The Great Energy Challenge.