"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 Patrick Mercier, a professor in the Department of Electrical and Computer Engineering at UC San Diego.
The development addresses the incompatibility of three competing wireless charging standards: Qi, Powermat and Rezence. Each wireless charger offered in the market to date supports either the Qi, Powermat, or Rezence standards, and will only work with devices that support the same standard.
The Qi and Powermat standards operate at around 200 kHz while the Rezence standard operates at 6.78 MHz. Wireless chargers are typically built with a transmitter coil optimized to work at a set frequency but are extremely inefficient at other frequencies.
The Mercier transmitter contains two coils; an inner coil optimized to operate at a frequency of 200 kHz, and an outer coil optimized to operate at 6.78 MHz. The design includes a filtering circuit to prevent the coils from interacting with each other and causing efficiency losses. Space is saved by putting the low-frequency coil inside the geometry of the high frequency.
At 25 mm separation, the system is able to simultaneously deliver 9 W and 7.4 W with efficiencies of 78% and 70.6% at 6.78 MHz and 200 kHz, respectively. The researchers have filed patents on this technology and are looking for commercial partners to help bring the universal wireless charger into the market.
For more, see the paper published in the journal IEEE Transactions on Power Electronics: Wireless Power Transfer with Concurrent 200kHz and 6.78MHz operation in a Single Transmitter Device.
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