This paper deals with the shielding of the magnetic field generated by two planar coils of a wireless power transfer (WPT) system at the frequency of tens of kilohertz used in automotive applications. Different shielding techniques using conductive and magnetic materials are examined and discussed highlighting strong and weak points of each other. Finally, the proposed shielding configuration consisting of a combined conductive and magnetic material is applied to model an electric vehicle equipped with a WPT charging system. With this configuration, compliance with the electromagnetic field safety standards can be achieved inside (passengers) or near (pedestrian) the car.

This paper reviews previous studies on metamaterials and its application to wireless power transfer (WPT) technologies, as well as discussing about development opportunities and technical challenges for the contactless charging of electric vehicles (EVs). The EV establishes a bridge between sustainable energies and our daily transportation, especially the park-and-charge and move-and-charge for EVs have attracted increasing attentions from the academia and the industry. However, the metamaterials-based WPT has been nearly unexplored specifically for EVs by now. Accordingly, this paper gives an overview for the metamaterial-based WPT technologies, with emphasizes on enhancing efficiency, increasing distance, improving misalignment tolerance, and compacting size. From the perspective of EV wireless charging, this paper discusses about the breakthrough to current WPT technique bottlenecks and prospective EV charging scenarios by utilizing the left-handed material. Meanwhile, the technical issues to be addressed are also summarized in this paper, which aims to arouse emerging research topics for the future development of EV wireless charging systems.

In this paper, an experimental study is carried out while charging the sealed lead acid battery bank using a series-parallel (SP) compensated contactless power transfer (CPT) system. Constant current (CC) and constant voltage (CV) modes are used for charging the battery bank. An expression of optimum operating frequency is derived to maintain the maximum compensated coil efficiency throughout the load variation in charging process. An experimental setup of SP compensated CPT system is built for charging the battery bank. The variation of compensated coil efficiency and the load phase angle with respect to different operating frequencies in CC and CV modes is verified with the measurement. Based on the analysis, the control parameters are identified.

In this paper, a resonant inductive wireless power transfer link using a relay element is analyzed. Different problems of practical interest are considered and solved by modeling the link as a lossy two-port network. According to the two-port network formalism, the standard gain definition (i.e. the power, the available, and the transducer gains) are used for describing the network behavior. Firstly, the case of a link with given parameters is considered and the analytical expressions of the optimal terminating impedances for maximizing the link gains are derived. Later on, the case of a link with given source and load is analyzed and the possibility of maximizing the performance by acting either on the transmitting or on the receiving side is investigated. It is shown that by using a single relay element, it is not always possible to maximize all the figures of merit that could be of interest in the WPT context. Theoretical data are validated by comparisons with circuital simulation results.

A preliminary numerical analysis of the power transfer efficiency (PTE) for the forward link of near-field (NF) ultra high frequency (UHF)-radio frequency identification (RFID) systems is addressed in this paper, by resorting to an impedance matrix approach where the matrix entries are determined through full-wave simulations. The paper is aimed to quantify the NF-coupling effects on the PTE, as a function of the distance between the reader and tag antennas. To allow for a PTE comparison between different reader and tag antenna pairs, a benchmarking tag-loading condition has been assumed, where the tag antenna is loaded with the impedance that maximizes the PTE. In a more realistic loading condition, the load impedance is assumed as equal to the conjugate of the tag antenna input impedance. Full-wave simulations use accurate antenna models of commercial UHF-RFID passive tags and reader antennas. Finally, a “shape-matched antenna” configuration has been selected, where the reader antenna is assumed as identical to the tag antenna. It is shown that the above configuration could be a valuable compact solution, at least for those systems where the relative orientation/position between the tag and reader antennas can be controlled, and their separation is of the order of a few centimeters or less.

In this paper, a theoretical study for the design of multi-source transmitters suitable for perpendicular dynamic wireless power transfer is presented. Unlike conventional systems, the concept presented here overcomes the traditional limitation on the receiver's orientation by providing an optimal distribution of the transmitted energy obtained by using different sources. For this purpose, a theoretical study of different transmitters has been achieved by solving the inverse problem. Comparison with conventional single-source transmitters carrying the same total current as the multi-source transmitters, shows a significant enhancement of the power gain when a Genetic Algorithm is used. The obtained theoretical results show power gain levels over 7.5 dB for different path lengths at different heights. At the end, a solution for a path of an infinite length is presented.

Impedance matching is very important to improve transmission efficiency not only for wireless communication but also for wireless power transfer. Lumped reactive elements are usually used in the impedance matching circuit. These reactive components such as inductors and capacitors have ohmic loss. An exact approach to design the lumped matching circuit at the presence of the ohmic loss is derived in this paper. Moreover, the condition for selection of impedance matching topology is deduced not only for lossless case but also for lossy case. Finally, the effect of the ohmic loss in the impedance matching circuit on the transmission efficiency is demonstrated quantitatively.