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Compatibility isn't an issue with this universal wireless charger

14 October 2015

Engineers at UC San Diego have developed a new technology for concurrently powering multiple devices that support different wireless standards.

The prototype set-up pictured side by side on the platform. The transmitter coils and receiver coils are attached to green circuit boards (photo: UC San Diego Jacobs School of Engineering)

A wireless charger that's compatible with different consumer electronics from different brands is one step closer to becoming a reality thanks to research by electrical engineers at the University of California, San Diego.

Researchers have developed a dual frequency wireless charging platform that could be used to charge multiple devices, such as smartphones, smartwatches, laptops and tablets, at the same time, regardless of which wireless standard each device supports.

"To our knowledge, this is the only multi-standard wireless power transmitter that's been shown to operate simultaneously at two different frequencies with high efficiency," says UC San Diego's Professor Patrick Mercier who led the study.

The new proof of concept study not only presents a "universal wireless charger" that can deliver power to multiple devices concurrently, it addresses an issue that afflicts existing wireless technology: incompatibility between the three competing wireless standards (Qi, Powermat and Rezence). Each wireless charger so far supports either the Qi, Powermat, or Rezence standard and will only work with devices that support the same standard.

"We developed a wireless technology that is universal and supports all of these standards so it won't matter which standard your device supports," says Mercier.

A wireless charger's ability to operate at a particular frequency depends on its transmitter coil. Wireless charging generally requires the charger's transmitter coil to send a high-power signal out to a compatible receiver coil in the device-to-be-charged. Existing wireless chargers are typically built with a transmitter coil that's optimised to work at one frequency. But as a consequence, the chargers are extremely inefficient at other frequencies.

The prototype set-up pictured with the two receiver coils off the charging platform. The transmitter coils and receiver coils are attached to green circuit boards (photo: UC San Diego Jacobs School of Engineering)

To address this problem, Mercier and his team built a charging platform capable of simultaneously operating across the frequencies supported by all three wireless power standards. The prototype that they built is a thin, rectangular box (12.5cm × 8.9cm) that contains two transmitter coils: an inner coil optimised to operate at a frequency of 200kHz, and an outer coil optimised to operate at 6.78MHz.

One of the features of this design is that the coils lie in the same plane, allowing for a compact size. The platform is just big enough to fit two smartphones side by side. Another important feature of the prototype is a filtering circuit that the researchers designed to prevent the coils from interacting with each other and causing efficiency losses.

The researchers demonstrated that the charging platform was able to deliver power to both receiver coils at the same time at efficiencies ranging from 70 to 80 percent. The receiver coils were also able to receive power regardless of where they were placed on the charging platform.

The researchers have filed patents on this technology and are looking for commercial partners to help bring the universal wireless charger into the market.

The work is published in the journal IEEE Transactions on Power Electronics.

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