Charge Your Phone (and Your Car) from Afar
Charging systems that send power farther through the air will soon be on sale.
Eric Giler points a remote control at a small black pad leaned up against a wall, and three lamps instantly light up and a tablet computer starts charging. The funny thing is, the devices all sit several feet away from the black pad, which provides power, and aren’t plugged in.
Giler is the CEO of Witricity, a startup that hopes to revolutionize electronics by replacing wireless charging systems with ones that send power safely through the air. The nearly five-year-old company uses technology developed at MIT that extends the range of inductive wireless charging.
Witricity says its first products—for charging portable electronics—could be on the market later this year. Within a year or two, similar technology could allow electric-vehicle owners to charge their cars without plugging them in. This could be followed by wireless power for heart pumps and other medical implants.
The idea of wireless power transfer is hardly new. Nikola Tesla demonstrated a version of it a hundred years ago, and inductive chargers for electric toothbrushes and video game controllers are now widespread. But the inductive chargers available today work over only very short distances and require physical contact between the charger and electronic device, which isn’t much more convenient than plugging a device in.
Inductive charging systems work by passing a current through a coil to generate a magnetic field, which creates another electric current in a similarly sized and oriented coil in the other device. Move these coils apart, and the efficiency of energy transfer drops off quickly. To increase the distance at which the power is transferred efficiently, Witricity tunes the sending and receiving coils to resonate with each other at a specific frequency with very little energy loss within each resonator.
The distance that power can be transferred in this way depends on the size of the coils. If both the sending and receiving coils are small, as may be the case with a system for mobile phones, the charger and the phone need to be placed within several centimeters to charge efficiently. But Witricity has also shown prototypes with larger coils that can send power at distances of about a meter. (Power can also be beamed with lasers and microwaves, but this requires a direct line of sight and can raise safety concerns.)
It’s also possible to boost the signal with coils called repeaters. In the demonstration Giler gave, coils installed under carpet squares allow power to leapfrog from a wall outlet to anywhere in the room.
Witricity is one of a handful of companies working to extend the range of electric chargers. The company has developed a prototype table that charges devices placed anywhere on its surface—even if they remain inside a backpack or purse—and a wireless keyboard and mouse that can be powered from a computer monitor, eliminating the need for batteries. (Apple has patented a similar idea.) The company has also developed a charger for electric cars. It’s a half-meter-wide pad that sits on the floor of a garage—just drive over it, and the car starts to charge.
Witricity is partnering with several companies to bring the technology to market. It has a multimillion-dollar contract with Toyota to develop charging for battery-powered vehicles (soon it might not make sense to call them plug-in electric vehicles), and has also announced a partnership with Taiwanese electronics manufacturer Mediatek to develop products for charging portable electronics.
Katie Hall, Witricity’s chief technology officer, says the company is working on components that will add the necessary electronics to a portable device. It’s also working to make charging sleeves for mobile phones that are no larger than the covers people typically use to protect their phones. The company isn’t certain how much these will cost, but Hall says the system for charging cars wouldn’t cost much more to make than the chargers that electric-vehicle owners often install in their garages anyway.
Several other companies are developing inductive chargers that can send power efficiently through the air. Siemens and BMW are developing chargers for electric cars, and Qualcomm recently bought a startup that had developed its own wireless electric-car chargers. A company called Fulton Technologies has technology that sends wireless power through a few centimeters of marble, as well as from the floor of a garage to an electric vehicle.
A handful of researchers are even working to extend the concept to allow charging of electric vehicles while they are out on the road. Researchers at Oak Ridge and Stanford recently developed detailed concepts for such a system. In a $2.7 million federally funded project, researchers at Utah State University are installing a system to charge buses as they stop along a route in Salt Lake City.
In the Oak Ridge model, 200 coils would be embedded in a section of the roadway and controlled by a single roadside device; successive coils would be energized as electric vehicles pass over them, providing enough power for the vehicle to reach the next series of coils a mile down the road.
John Miller, a research scientist at Oak Ridge, estimates that each series of coils plus the controller would cost less than a million dollars. “Wireless chargers for electric vehicles are so convenient. You don’t have to mess with plug cables. You don’t care what the weather is. You don’t even have to think about it. I think it’s going to catch on superfast,” Miller says.
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