This article presents the existing challenges of coil selection in a multi-coil power transmitter system. If a transmitter coil with large mis-alignment to the receiver coil is selected for wireless power transfer, protection will trigger, leading to poor user experience. Finite element analysis (FEA) and circuit modeling study find that extending the receiver coil’s magnetic shielding in the direction of a misaligned transmitter coil can increase this specific transmitter coil’s self-inductance, and thus avoid false selecting it in a digital ping phase. Two receiver coil samples with and without the extended shielding are tested. Experimental results verify that the proposed receiver coil design can improve the transmitter coil selection without side effects on normal operation.
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