A wireless charger that supports multiple frequencies in order to charge devices with different standards has been developed by electrical engineers at the University of California. The charging platform could be used to charge 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 the study’s lead, professor Patrick Mercier.
Ref: Wireless Power Transfer with Concurrent 200 kHz and 6.78 MHz operation in a Single Transmitter Device. IEEE Transactions on Power Electronics (2015) | DOI: 10.1109/TPEL.2015.2480122
This paper proposes a wireless power transfer (WPT) transmitter that can concurrently operate at 200 kHz and 6.78 MHz in order to simultaneously power two receivers operating with different frequency standards. Unlike a dual-resonant single-coil design, the use of two separate coils decouples the design for one frequency from the other, enabling independent selection of inductance and Q-factor to simultaneously maximize efficiency at both frequencies. The two coils then support separate coil drivers, enabling concurrent multistandard operation. Dual-band operation is achieved in the same area as an equivalent single-band design by placing a low-frequency coil within the geometry of a high-frequency coil, where the outer diameter of inner coil is sacrificed only by 1.2 cm in a 12.5 × 8.9-cm2 design. Circuit analysis is presented to identify the eddy current between the two Tx coils and its associated loss, after which an eddy-current filter design is proposed. To validate the proposed design, a dual-mode transmitter, along with two receivers designed at 6.78 MHz and 200 kHz, respectively, have been fabricated. At 25-mm separation, the system is able to simultaneously deliver 9 and 7.4 W with efficiencies of 78% and 70.6% at 6.78 MHz and 200 kHz, respectively.