High-Impedance Wireless Power Transfer Transmitter Coils for Freely Positioning Receivers

In this letter, a wireless power transfer (WPT) system based on two high-impedance coil (HIC) - cable loop antennas with a modified shield - as transmitters (Tx)s and a spiral coil as a receiver (Rx) is proposed and discussed. Utilizing features of HIC at its parallel-circuit resonance frequency, we design the Tx in a way that in the absence of the Rx, the input impedance of the Tx is very high compared to the case when the Rx is near the Tx. This feature offers a possibility for free positioning of the Rx over an array of Txs and auto self-activation and de-activation of the Txs, leading to highly efficient performance. To verify the proposed solution, we have designed, fabricated, and experimentally tested a WPT system based on two HICs as Txs and one Rx. The proposed system operates in a high-frequency range (around 280 MHz) in the near-field coupling regime. The measured averaged efficiency of the prototype is higher than 93%. The proposed system is simple, cheap, and does not require any control circuit system for tuning the system when the receiver position changes.