Abstract
Wireless power transfer technology via magnetic resonance coupling now has significant interest in industry and research with many applications. This paper proposes a linear multiple transmitter coil array (5 coils) for wireless power transfer for added gain and hence higher transfer efficiency in comparison to a single transmitter coil. The frequency splitting effect as a result of the coupling between the resonant transmitter coils due to their close proximity is shown to reduce the transfer efficiency to a receiver. The effect of the array spacing on splitting effect suppression is verified. It is shown that the splitting effect is sup-pressed as the distance between the coils is increased leading to a higher received signal and hence higher efficiency. Proposed horizontal displacement of the middle transmitter coils (2nd and 4th coils) in the coil array is shown to suppress frequency splitting. To further suppress the splitting effect due to the magnetic coupling between the transmitter coils, a multiple transmitter array is proposed with different coil turns. Thus it is shown that designing the multiple coil array with mixed number of coil turns (the 2nd and 4th coils are designed to have different number of turns as compared to the other three coils) causes uniform coupling among the coils reducing and eventually eliminating the splitting effect. Also to increase the efficiency at the receiver coil, displaced stacked coils are introduced on top of the coil array. The pro-posed stacked coil array is demonstrated to improve the transfer efficiency. Using the techniques, the proposed linear array structure achieves a transfer efficiency of 36.9% for a receiver coil at the boresight of the array at a transfer distance of 40 cm.
Highlights
Wireless power transfer is electrical energy transmission using time varying electromagnetic fields without the use of wires
Wireless power transfer provides a useful solution of powering electrical devices in situations where interconnecting wires are a downside, hazardous or not applicable
High efficiency is achieved with inductive coupling as far as the coils are close together and on the same axis
Summary
Wireless power transfer is electrical energy transmission using time varying electromagnetic fields without the use of wires. The increase in the number of transmitters was found to increase the gain of the system, increase in the transfer efficiency This phenomenon is shown to occur when the transmitters are far away from each other such that there is negligible coupling between adjacent coils. Coupling between adjacent transmitter coils, there is a frequency splitting effect of the received signal at the receiver This phenomenon reduces the transfer efficiency at the receiver and suppression and elimination of the splitting effect increases the efficiency [6, 7]. The design of a proposed structure where the middle coils in the multiple coil array are displaced horizontally suppresses and eventually eliminates the splitting effect and enhances the efficiency. As compared to the multiple transmitter coil structure in [6] which achieves a transfer efficiency of 11% at 40 cm, the proposed structure achieves 36.9%
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