“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 lead researcher Patrick Mercier. The wireless chargers that are on the market today are only compatible with one of three competing wireless standards—Qi, Powermat and Rezence. The Qi and Powermat standards operate at around 200 kHz but Rezence operates at 6.78 MHz. So, in order for the new wireless charger to work with a wide variety of devices, the engineers designed it to operate at both frequencies.
Mercier and his team built a charger that has two transmitter coils—one for each frequency. An inner coil optimized to operate at a frequency of 200 kHz (for Qi and Powermat devices), and an outer coil optimized to operate at 6.78 MHz (for Rezence). In order to keep the design compact, the coils lie in the same plane. The prototype has a filtering circuit which prevents any potential efficiency loss that could be caused by the coils interacting with each other.
The researchers then tested the proof of concept prototype using two receiver coils (one for each frequency), which represented two smartphones on different standards. The engineers demonstrated that the charging platform delivered power to both receiver coils at the same time, no matter where the coils were placed on the platform. Even when the two receivers were charged at the same time, the power transferred at 70 to 80 percent efficiency.
The researchers have filed patents on this wireless technology and are now looking for partners to help commercialize a universal wireless charger. The work is described in a paper published in the journal IEEE Transactions on Power Electronics.
