Wireless power transfer for free positioning using compact planar multiple self-resonators

In this paper, a wireless power transfer (WPT) system supporting free positioning in a large area is proposed. The main coupling unit of the proposed system consists of a transmitter with 5 self-resonators and a receiver with a self-resonator. By circuit analysis, the proposed system is analyzed. The fabricated coils are compact planar rectangular spiral types. The total size of the transmitter is 96 cm × 16 cm. The receiver is 10 cm × 10 cm. With the exception of the 5^th resonator in the transmitter, their resonant frequencies are 6.78 MHz. There are some regions with less than 50% power transfer efficiency (called a dead zone). By changing the 5^th resonator´s frequency, the area of the dead zone can be reduced. When the 5^th resonator´s resonant frequency f₅ is 6.78 MHz, a system has 40% dead zone of the transmitter and power transfer efficiencies of 57% ~ 87% in the other regions. On the other hand, when f₅ is 6.38 MHz, a system has 10% dead zone and power transfer efficiencies of 70% ~ 86% in other regions. The measured power transfer efficiencies are approximately consistent with the calculated results.