The concept of being able to charge up a depleted battery without a cord or plug in sight might seem futuristic. But more than a century after Nikola Tesla demonstrated wireless energy transfer, wireless charging systems are already becoming a reality for devices ranging from electric toothbrushes and mobile phones to artificial hearts and LCD televisions. For electric cars, industry analyst Richard Martin and research firm Pike Research predict in a new report that wireless power stations designed for home installation could dramatically speed up adoption of these vehicles. "If many residences, businesses, public parking garages, and so on could be outfitted with 'hand-off' wireless charging systems that essentially recharge the car each time it is parked," writes Martin, "one of the major points of friction for the EV market would be eliminated." In short, driving an electric car in a world with ubiquitous wireless charging options would mean ditching the gas pump without taking on the trouble of charging equipment.

"Consumers will appreciate hands-free charging everywhere," commented Britta Gross, General Motors' R&D and Strategic Planning Director for Global Energy Systems. "Outdoors comes quickly to mind, but even at home hands-free charging would have meaningful value to many consumers." Wireless charging could save time, she said, but mostly it would save the "hassle of plugging in and out."

Among the companies hoping to offer wireless charging systems for electric cars are auto parts maker Delphi and WiTricity Corp., an MIT spinoff working on technology to transfer electric power over distances of up to several meters. At the Plug-in 2010 conference this summer in San Jose, Calif., a company called Evatran unveiled a system for charging electric vehicles with "proximity charging," which would work with a receiver positioned only up to about two inches away from the transmitter. And in the latest alliance formed around wireless power in 2010, Delphi and WiTricity teamed up this fall to develop plug-free products for automatically charging electric vehicles.

How It Works

Here's how Delphi and WiTricity's system is supposed to work: You would carefully park an electric vehicle over a 3.3-kilowatt pad set into pavement or your garage floor. Leaving the car aligned over that pad, you would find the battery fully charged after a few hours (depending on the starting charge level and the size of the battery). In order to make use of the system, cars would have to be outfitted with a receiver.

Wireless power technology can take several forms. Kits are sold (for about $80-$100) today for charging portable devices like phones and cameras by simply placing them on top of a mat. Other systems require no physical contact at all. As the Pike Research report points out, a "room-based system" can charge all electronic devices in a given range or volume. Several different technologies can be used to deliver plug-free power, including induction, conduction, radio-frequency and microwaves, and lasers.

WiTricity's technology involves what's called magnetically coupled resonance (a form of inductive coupling). A copper coil embedded in the parking spot is attached to an AC power source and creates an electromagnetic field in the area around the coil. This is the "sending unit."

When a second copper coil installed in the vehicle is close enough to the sending unit, it can convert the magnetic energy to alternating current (Martin notes that "only specially designed coils can respond" to the electromagnetic field). This is the receiving unit or capture device.

WiTricity uses electronic systems to dynamically "tune" or control this exchange of energy and make it more efficient. That's an important piece of the puzzle for wireless power. As Megan Hayes, Senior Manager of the Consumer Electronics Association's Technology and Standards Group, said in an interview, "wireless power will never be as efficient as plugging into your wall." According to WiTricity, its system is most efficient (with only about 5 percent power loss) when the sending and receiver units are closer together.

Charging Not Just Vehicles, But Gadgets

In conventional vehicles, wireless power technology could come into play much sooner than wireless charging systems for electric cars, as a means for charging mobile devices on the road without a tangle of cords and adapters. "The idea of being able to go into my partner's vehicle and not have to worry about charging," said Hayes, "that's very appealing."

Wireless charging is one of those technologies that seems always to be "just around the corner" from widespread implementation, and Gross expects wireless charging for vehicles to remain the province of demonstration projects in the near term. But according to Martin's estimates, adoption of wireless power charging and transmission devices will increase steadily during the next five years. After that, they forecast that consumer adoption of the technology will accelerate rapidly, making its way into many everyday products and generating $11.8 billion in revenue by 2020.

Today, wireless power charging still faces plenty of hurdles to widespread use in vehicles. According to Pike Research, two of the biggest challenges include regulations and questions about public safety. "Even though the magnetic and electromagnetic fields produced by these systems are demonstrably harmless," writes Martin, "vendors must wrestle with wide public mistrust of the idea of wireless transmission of electricity."

There's also the issue of interoperability, which an industry working group is seeking to resolve for consumer electronics by developing a set of standards. "A lot of companies are working in this space, big and small," said Hayes, "and they're all working on their own flavor." The interface between the coil and device, she explained, is proprietary to each system. As a result, a smartphone equipped with a receiver for a charging mat from one company might not work with the wireless charging system produced by another. In addition, there is not a standardized way for reporting efficiency, making it difficult for consumers to find out which wireless charging system will offer the most bang for the buck.

At this point, said Hayes, automakers are generally "monitoring but not actively participating" in the standards development process for wireless power. Down the road, however, interoperability -- being able to juice up at any equipped parking spot, regardless of a car's make and model -- will be key for wireless charging systems to provide the predicted boost for electric vehicles.

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