Design of a Wireless Power Transfer System using Electrically Coupled Loop Antennas

Abstract

Wireless Power Transfer (WPT) has become quite popular over the recent years. This thesis presents some design challenges while developing a WPT system and describes a system-level methodology for designing an end-to-end system. A critical analysis of contemporary research is performed in the form of a literature survey of both academic and commercial research to understand their benefits and demerits. Some theoretical notes are presented on coupled-mode theory and coupled filter theory and the problems concerning WPT analyzed using these models. The need for higher power transfer efficiency (PTE) and power delivered to load (PDL) is studied using these models. The case for using magnetic antennas over electric antennas when surrounded by lossy media (specifically for the case of human body tissues at various frequencies) is made using some theoretical models and simulation results. An Electrically Coupled Loop Antenna (ECLA) is introduced, studied and designed for two main WPT applications, viz. free space transmission and that of powering implanted devices. An equivalent circuit is proposed to better understand the coupling effects of the antennas on a circuit level and to study the effect of various environmental and structural factors on the coupling coefficient. Some prototypes were created and measured for the two use cases of free space and implanted applications. In order to complete the system design, a negative resistance-based oscillator is designed and fabricated, that incorporates the antennas as a load and oscillates at the required frequency. Some changes in load conditions and power handling are studied by the use of two circuits for free-space (high-power) and implanted (low-power) applications. Finally, the salient points of the thesis are re-iterated and some future work outlined in the concluding chapter.