Wireless power transfer with extended distance and power regulation

Abstract

This thesis starts with the basic review of magnetically resonant coupled Wireless Power Transfer (WPT). The concept of reflected impedance (admittance) is introduced to analyze the efficiency of WPT. General guidelines to obtain high efficiency at longer distance are explained. Based on the above discussions, we investigate the effect of coupling between multiple transmitters (Tx) or between multiple receivers (Rx). We propose the required frequency adjustment to compensate the variation of the effective resonant frequency. Next, we study the magnetic field repeater resonator, which is placed between Tx and Rx, to enhance the power transfer distance. We propose the guidelines to select the optimum repeater positions and numbers. We also propose a new kind of repeater which can be placed even in the vicinity of Tx or Rx, resulting in increased flexibility in choosing the position of a repeater. Third, we propose a method to boost the coupling between Tx and Rx, by using Tx or Rx consisting of multiple separate resonators. In this way, the distance of power transfer is significantly increased. The final part of this thesis is on the WPT to the miniature biomedical implants. The considerations for such biomedical implants are low thermal dissipation, minimum number of component, and lightweight coil. To satisfy these considerations, we propose a design methodology which can obtain high efficiency even with the integrated CMOS power amplifier and planar PCB coil, rather than using bulky discrete FET and heavy solid copper wire. More importantly, the transferred voltage is controlled to maintain a constant level regardless of the variation of coupling or loading.