Rigorous Network and Full-Wave Electromagnetic Modeling of Wireless Power Transfer Links

The proposed approach makes use of full-wave electromagnetic modeling of wireless power transfer links in order to derive the network characterization, e.g., in terms of scattering or impedance matrix. Once the latter is obtained, we show that network theory provides the appropriate matching impedances for achieving either maximum efficiency, maximum power on the load, or conjugate matching. The proposed approach also permits to derive closed-form matching networks and expressions for power and efficiency. An example of full-wave numerical electromagnetic modeling of a wireless power transfer link is presented. The selected example, which is similar to the experiment published by Kurs et al., shows the importance of selecting the appropriate source/load impedance for obtaining significative results.

I. Introduction

At present, there is considerable interest among researchers in wireless power transfer (WPT). In [1], the authors have shown power transmission at a distance of 2 m. In particular, a 60-W bulb has been lightened up. In this case, the wireless power system has been made by using two self-resonant spiral resonators. The transmitting coil has been inductively coupled to an oscillating circuit, while the receiving coil has been inductively coupled to a resistive load. The experiment has been conducted at a frequency of 9.9 MHz. Initially, coupled-mode theory was used for the analysis [1], [2]. Later, a network approach has been used by several authors, e.g., in [3]–[5]. Subsequent research has addressed the problem of mid-range wireless energy transfer by always considering the coupling between resonant networks [6]–[9]. In [10]–[12], efficiency investigations have been presented, together with appropriate network representations [13] always considering coupled resonators.