Nulls-Free Wireless Power Transfer With Straightforward Control of Magnetoinductive Waves

We present a straightforward and yet, effective method to modulate the termination impedance of 1-D LC resonating arrays for wireless power applications. The modulation method is based on activating/deactivating the last two cells of the array allowing to remove the power nulls caused by standing waves inside this type of arrays. The modulation of the terminating impedances is done at a distinct frequency than the resonance frequency of the cells. We explain why and how this distinct frequency was chosen. We further demonstrate how the same modulation is applicable for a wide range of load resistances on the receiver device. Modulation is achieved by wirelessly sensing the voltage delivered by the power supply according to where above the array a receiver device is located. A microcontroller records these voltages and determines which terminating impedance will provide the highest possible efficiency to the receiver device. Changes in the terminating impedances are set by digitally controlled solid state relays. The proposed modulation method permitted to power up a receiver device with a system efficiency of up to 60% anywhere over the 30 cm length of the resonating array.