Imagine an electric car that charges up as it’s zooming along the highway. The road is the charger, able to wirelessly transmit power to a vehicle while it’s in motion.
This vision could be a step closer thanks to work by Stanford University researchers, who have come up with a new way to transfer power to an appliance even as it moves away from the source. The team, led by Shanhui Fan, showed that they could provide continuous wireless power to an LED light bulb while they moved it away from the power source, up to a distance of about one metre. They published their results in Nature.
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Fan explains that most existing wireless charging systems require the object being charged to stay in a specific position. If you take two similar coils of wire and excite one with a source of radio waves, the other will couple with it and the two will act like a single circuit, with the first transferring power to the second. But the frequency of the radio waves has to be carefully tweaked for this to work well with any given distance between the coils.
“For stationary charging this is not an issue, because you know the distance and you can always tune the circuit to the optimum condition,” Fan told WIRED. “But if you are thinking about dynamic charging, when the distance constantly varies, then you need to continuously tune the circuit in order to maintain the efficiency.”
If you were charging you phone this way, for instance, you’d need to place it in just the right spot near the charger.
So Fan and his colleagues developed a new technique, drawing on ideas from quantum mechanics. Their system automatically adapts to the optimum conditions for power transfer as the coils move closer and further away. To do this, they use what is called a “parity-time symmetric circuit”. Where the first coil would usually be driven by a source of radio waves, they get rid of that and instead put an amplifier directly into the coil – so it’s essentially creating the waves it needs itself.
Geoffroy Lerosey, a research scientist at the Institut Langevin in Paris who wrote a commentary to accompany the Nature article, compares the effect to audio feedback from an electric guitar placed at a certain distance from a speaker. “There’s a huge sound that auto-creates in the system due to the fact you have an amplifier,” he says. “The system is picking up one frequency, and this frequency is amplified and amplified and amplified to create this huge sound.”
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Lerosey says this is a really novel way of thinking about wireless power transfer, and describes it as an “ingenious strategy”.
For now, the researchers have only experimentally tested their system with an LED bulb – which requires a lot less power than a car. Higher power levels could pose issues of practicality, and the system would have to be able to adapt quickly enough to accommodate fast speeds. But if limitations can be overcome, the idea is that an array of coils on the road could transfer power to a coil in a vehicle as it passes over them.
Meanwhile, Fan says there are plenty lower-power applications that could benefit from the technique - it could be used to wirelessly charge implantable medical devices, for example.
And for Fan, it’s nice to see a new application for a fundamental concept in quantum mechanics. “I always find it fascinating how a very basic concept can show up in application somewhere unexpectedly,” he says.
This article was originally published by WIRED UK
