To Charge Electric Cars, Just Drive

Electric vehicle recharging techniques run the gamut from fast-charging setups to battery swap-outs to wireless charging stations. Electrical engineers at Stanford propose the most convenient of them all: just drive.

A team led by associate professor Shanhui Fan, including postdocs Xiaofang Yu and Sunil Sandhu, are working on it. They'd like to embed metal coils several feet apart in a stretch of highway and outfit an EV with its own coil. Then, as the vehicle drives down the highway, the embedded coils would wirelessly recharge the car's battery.

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Sounds too good to be true, but the phenomenon -- called magnetic resonance coupling -- has already been proven. It works like a secret message: When copper coils are tuned to resonate at the same frequency, one coil that's hooked up to an electric current can pass it to the other coil through a unique magnetic field. The transfer requires special tuning so anything that's not tuned the same way -- including humans -- won't be affected.

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Five years ago, a group at MIT lit a 60-watt lightbulb using magnetic resonance and a spinoff from the Institute called WiTricity created power mats that wirelessly recharge devices this way. MIT physicists also found that the efficient power transfer is safe for humans and animals.

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Fan and his colleagues used computer models to come up with a coil array that could transfer 10 kilowatts to an EV. They found that coils bent at 90 degrees, each with a metal plate, spaced 6.5 feet apart would do the trick. They published their results (PDF) in the journal Applied Physics Letters and recently filed a patent application.

Next, the electrical engineers plan to test the setup using computer simulations in the lab and then create a real prototype to make sure the system works as expected.

I still hear about "range anxiety" whenever there's the hint of EV recharging. We should be well past this. With magnetic resonance, it's time to put those fears to rest -- under the highway.

Photo: Stanford postdoc Xiaofang Yu points to a computer rendering showing how wireless EV charging on the highway would work. Credit: Mark Shwartz, Precourt Institute for Energy, Stanford University.

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