Wireless Sources Might One Day Charge Electric Vehicles as They Move

Stanford researchers transmitted a 1 milliwatt charge to a moving LED lightbulb — a feat that they hope can be scaled up to power electric vehicles on a roadway.

Remote power is not new. In the 1960s, scientists wirelessly charged a hovering miniature helicopter using microwaves. Wirelessly charging smartphones have been around for a few years, too.

Distance between objects is not a barrier to exchanging power, said Sid Assawaworrarit, an Ph.D student at Stanford and lead author of the researchers’ study, which is published in the journal Nature. Rather, he said, it’s how they interact in space.

“People usually think that the closer you are to the source, the better you get power transfer,” he said. “But the counterintuitive fact is that it’s the importance of tuning that you need.”

Wireless charging has faced challenges going mainstream because, until now, energy sources and their recipients have had to remain stationary to transfer power. Moving them would break the magnetic connections that deliver energy between the two.

One could attempt to adjust the magnetic connections between two objects to keep them charging, but that’s too difficult, the Stanford researchers said. Instead, they adjusted voltage and feedback to produce an instant connection that kept charging even as the energy source and the recipient moved.

The team transmitted a 1 milliwatt charge to a moving LED lightbulb.

“For anything that could benefit from dynamic, wireless charging, this is potentially very important,” said Stanford electrical engineer Shanhui Fan, the study’s senior author, in a university news release.

Assawaworrarit compared the process to tapping into the energy released from microphone feedback. “You have some sort of gain element, amplified in a circuit, the frequency of feedback noise,” he said. “It’s the same.”

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Electric cars usually require tens of kilowatts to drive. But if the team could scale up their findings, the implications were most promising for green vehicles, the engineers said.

Stanford’s TomKat Center for Sustainable Energy provided partial funding for the project.

Currently, electric cars tend to have ranges of around 200 miles before they need a recharge that can take hours, the researchers said. Car companies are racing to extend that range. But it might be far enough if the cars were charged more frequently.

“We still need to significantly increase the amount of electricity being transferred to charge electric cars, but we may not need to push the distance too much more,” he said, adding that the goal would be to revamp the country’s infrastructure.

“In theory, one could drive for an unlimited amount of time without having to stop to recharge,” Fan said. “The hope is that you’ll be able to charge your electric car while you’re driving down the highway. A coil in the bottom of the vehicle could receive electricity from a series of coils connected to an electric current embedded in the road.”

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