Design analysis and realization of compact energy efficient RF wireless power transfer systems

Abstract

Nowadays, wireless power transfer (WPT) has become a top area of research due to ease and portable outcome in the present technological scenario. This creates an increased demand globally in various technological sectors such as consumer electronics, bio-medical implants, automotive industry and so on. In consumer electronics, wireless power transfer is used in wireless charging of electronic devices. For example, mobile devices are required to be plugged in manually for charging which limits mobility and disrupts use when charge is depleted. In addition, due to compactness in the overall size of the portable device, the connectors become a larger fraction of device size. As a result, the use of wireless power transfer technique eliminates the connector from portable electronic devices which improves both size and reliability. Furthermore, in biomedical implants, the use of non-rechargeable batteries needs replacement at the end of their life span by a costly surgery. Also, the bulky nature of non-rechargeable batteries creates an obstacle in the design of compact implantable devices. These concerns raise the requirement of wireless power transfer technique in modern applications. Furthermore, wireless power transfer is classified into two different types i.e. near field and far field WPT. This thesis mainly focuses on resonant inductive type near field WPT systems operating in MHz frequency range. This type of WPT system transfers power at higher efficiency and over longer distances than non-resonating WPT systems. In addition, these systems can also transfer power at mid-range separation distance where the distance of power transfer is greater than the size of the resonator. Most importantly, resonant inductive near field WPT is realized using different coil mechanisms i.e. litz/solid wire and printed circuit board (PCB) based spiral coils and planar microstrip line structures such as defected ground structures (DGS). Firstly, the coil mechanism based on litz/solid wire uses two similar coils separated by a dis