The prototype of the dual frequency charger is a thin, rectangular box (12.5 centimeters × 8.9 centimeters) that contains two transmitter coils: an inner coil optimized to operate at a frequency of 200 kHz (orange), and an outer coil optimized to operate at 6.78 MHz (red). The prototype setup is pictured with the two receiver coils off the charging platform (top) and side by side on the platform (bottom). The transmitter coils and receiver coils are attached to green circuit boards. Credit: UC San Diego Jacobs School of Engineering
Uni of CA, SD Electrical engineers 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, or frequency, 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,” said Prof. Patrick Mercier. 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 3 competing wireless standards in today’s market (known as 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.
These 3 standards operate under different frequencies: Qi and Powermat operate at around 200 kHz while Rezence operates at 6.78 MHz. So herein lies the challenge. In order for a single charging device to support multiple standards, it needs to operate across these very different frequencies.
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 optimized to work at one frequency. But as a consequence, the chargers are extremely inefficient at other frequencies.
To address this problem, Mercier and his team built a charging platform capable of simultaneously operating across the frequencies supported by all 3 wireless power standards. The prototype that they built is a thin, rectangular box (12.5 cm × 8.9 cm) with 2 transmitter coils: an inner coil optimized to operate at a frequency of 200 kHz, and an outer coil optimized to operate at 6.78 MHz. 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 2 smartphones side by side. Another important feature is a filtering circuit to prevent the coils from interacting with each other and causing efficiency losses.
The charging platform was able to deliver power to both receiver coils at the same time at efficiencies ranging from 70 -80%. The receiver coils were also able to receive power regardless of where they were placed on the charging platform.
“This means that multi-device and multi-standard wireless charging don’t have to come at a significant efficiency penalty,” said Mercier. http://jacobsschool.ucsd.edu/news/news_releases/release.sfe?id=1828
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