Wireless Power Transmitter and Receiver Supporting 200-kHz and 6.78-MHz Dual-Band Operation without Magnetic Field Canceling

The paper proposes a method to suppress the anticurrent and magnetic canceling in a dual-band transmitter (Tx) and receiver (Rx) for wireless power transfer. The problem of intracoupling between the two coils in a dual-band resonator is analyzed. During 6.78-MHz operation, the intracoupling causes antidirectional current at 200-kHz coil which cancels the magnetic field and degrades efficiency. To solve the problem of antidirectional current, a new resonator design method is proposed. The proposed technique suppresses the 6.78-MHz anticurrent by specially selecting the impedance values and coil-winding direction that manipulate the magnitude and phase of 6.78-MHz voltage, such that total voltage across 200-kHz path is zero. One of the advantages is that the spatial separation between 6.78-MHz coil and 200-kHz coil can be reduced, which allows the maximum diameter for inner coil. Also, smaller discrete inductor can be used. The two coils share an inverter (or a rectifier), thus minimizing the number of inverter and rectifier. The 24-W system with dual-band Tx achieves 70.3% and 70.8% efficiencies at 6.78 MHz and 200 kHz, respectively, whereas the system with dual-band Rx achieves 66.3% and 74.3% at 6.78 MHz and 200 kHz, respectively. The efficiency improvement due to anticurrent suppressing is 4.8~23.6%.