Abstract—The operation of wireless power transfer systems
with multiple transmitters (TXs) or receivers (RXs) is investigated.
With multiple TXs or RXs in a limited space, couplings
occur between TXs or between RXs. The frequency conditions
for maximum efficiency and power transfer under such couplings
are proposed. Effective resonant frequency of the TXs or the RXs
is changed due to such couplings, and driving and/or resonant
frequencies should therefore be adjusted accordingly. The amount
and type of the required adjustments are provided. The efficiencies
in these conditions are discussed. These concepts are supported
by experiments with couplings between TXs or between RXs.
Using the proposed frequency adjustments, 51–65-W power is
transferred with 45%–57% efficiency, even with very low coupling
coefficients of 0.025–0.063 from TX to RX. This improvement is
significant compared to the unadjusted cases where less than 4 W
is transferred with only 5%–33% efficiency.