Impedance Matching using Interspiraled Coils for Wireless Power Transfer

This paper presents switchable interspiraled coils suited for active impedance matching in magnetic resonance wireless power transfer. The impedance matching network consists of single-turn coils placed in-between turns of a spiral resonator coil. The inductance variation allows matching over a range of distances in Wireless Power Transfer (WPT) systems. Measurements of a 9 turn coil with radius of 103 mm is presented. The measured self-inductances of the single-turn coils vary between 43-510 nH. Measurement of the power transfer efficiency verifies that the proposed interspiraled coils offer an active impedance matching in the under-coupled region for distance changes between 7 cm to 25 cm. The interspiraled coils can be realized on one side of a PCB and the other side can be used for control circuitry and routing, making it compact in size and potentially cheaper in production.