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14 June 2017

Wireless charger uses quantum trick to power gadgets on the move

A fully charged mobile phone in a person's hand
Walk and talk and charge

Jorge Perez/Alamy Stock Photo

Wireless chargers for smartphones and other gadgets are convenient but there’s a hitch: you have to leave your device in one place while it charges. A new self-adjusting design means that your smartphone could continue charging when on the move.

Current wireless chargers work through magnetic induction: when a charger and device are tuned to resonate with each other. Although existing designs are efficient when the power source and device are a fixed distance apart, it’s more of a challenge if the device is moving.

Now Shanhui Fan from Stanford University and his team have developed a wireless charger that works even when a device moves up to a metre away from the power source. Its orientation can also change continuously without reducing the energy transfer. In a demo, the team was able to power a moving LED bulb without reducing its brightness.


To achieve the same thing with existing systems, circuits would need to be tuned constantly. “It adds complexity,” says Fan. “Our system is the first to achieve this without the need for active tuning,” he says.

The team did this by applying a concept that originated from quantum mechanics called parity-time symmetry. In this case, it involved coupling circuits in the charger and LED bulb so that the energy boost from an amplifier in the charger exactly balanced out the loss of energy as the bulb moved further away. The system automatically self-adjusts even when the distance between the bulb and charger changes. “I think it is interesting to see a basic physics concept find application in a completely different area,” says Fan.

Daniel Stancil from North Carolina State University in Raleigh thinks it’s an exciting idea. “A smartphone could be charged while you are holding it or using it, without having to put it on a charging station,” he says. Although there are other ways of achieving self-tuning circuits, he thinks that the new approach is simpler and could be less expensive to implement.

Fan and his colleagues are planning to improve the range of their charger. They will modify the design to increase the charging distance, which could be useful for powering moving vehicles for example.

Wireless systems could one day be used to beam power over much greater distances. Another group, for example, is looking at using lasers and balloons to send power to disaster zones. Ultimately, they hope to generate solar power in space and beam it to Earth. It could allow more energy to be harvested than is possible on Earth, since energy from the sun is lost when it passes through our atmosphere.

Journal reference: Nature, DOI: 10.1038/nature22404

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