We propose a loop switching technique to improve the efficiency of wireless power transfer (WPT) systems using magnetic resonance coupling. The proposed system employs several loops with different sizes, one of which is connected to the system with various distances between the transmitter and the receiver. It enables the coupling coefficient to be adjusted with the distance, which allows high efficiency over a wide range of distances. The proposed system is analyzed using an equivalent circuit model, and electromagnetic (EM) simulation is performed to predict the performance. It is shown from the experimental results at 13.56 MHz that the proposed loop switching technique can maintain high efficiency over a wide range. The efficiency is measured to be 50% at 100 cm, which corresponds to a 46% increase compared to a conventional WPT system without the loop switching technique.
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