I. INTRODUCTION
WIRELESS power transfer (WPT) is used in various ap- plication fields ranging from a few milliwatts in biomed-ical applications [1]–[3] up to several kilowatts of output power in automotive applications [4]–[6]. Currently, WPT systems in- tended to wirelessly charge consumer electronic devices, such as mobile phones or tablet computers, are studied extensively [7]–[10]. Various aspects of these systems are defined by several standards which are either based on nonresonant or inductive power transfer (IPT), like the Qi standard [11] or on resonant power transfer (RPT), like the Rezence standard [12]. In order to ensure interoperability of different transmitter and receiver devices, these standards define parameters such as the voltage range, the basic circuit structure, and the operating frequency of the system. The main drawbacks of currently available WPT systems for consumer applications are, amongst others, the rel- atively low overall efficiency and the limited power transfer capability. This results in long charging times which hampers the widespread application of the WPT technology.