This paper presents a new method for analyzing the maximum efficiency of a wireless power transfer (WPT) system with multiple n resonators. The method is based on ABCD matrices and allows transformation of the WPT system with multiple n resonators into a single two-port network system. The general maximum efficiency equation of a WPT system with multiple n resonators is derived using the ABCD matrix. Use of this equation allows placement of the relay resonators for maximum efficiency even though they are asymmetrical. The general maximum efficiency equation and the method of the optimum placement are verified by a full wave simulation. The results show that the method is useful for the analysis of a WPT system with relay resonators. This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/ by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. Ⅰ. IntroductionMany researchers are currently investigating magnetically coupled wireless power transfer (WPT) systems. A conventional WPT system consists of two main resonators for the transmitter and receiver, which operate at the same resonance frequency [1][2][3]. This system, however, has a limitation on the distance between transmitter and receiver for achieving high WPT efficiency. This limitation can be overcome by using some resonators as relays between the two main resonators [4]. The WPT system is then composed of multiple n resonators, which can achieve a higher WPT efficiency than a conventional WPT system can at the same distance. This system is well analyzed in [5] with respect to the general circuit model and the maximum efficiency with a matched load. However, the general maximum efficiency equation of a WPT system with multiple n resonators described in [5] becomes complicated when analyzing the type of system normally utilized for practical applications.This paper proposes a new analysis method for the WPT system with multiple n resonators. The method simplifies the entire WPT system into a single two port network expressed by an ABCD matrix. The general maximum efficiency equation of the WPT system with multiple n resonators can then be obtained with elements of the ABCD matrix. This equation provides a much more convenient way to obtain the maximum efficiency and the optimum placement of the asymmetrical relays for the best utilization. The general maximum efficiency equation and the method of the optimum placement of the asymmetrical relays are verified by a full wave simulation of ANSYS HFSS (high frequency structural simulator). Ⅱ. New Analysis Method Using the ABCD MatrixThe schematic diagram of a WPT system with multiple n resonators is shown in Fig. 1(a). The non-adjacent coupling coefficient is ignored since it is very small in a practical WPT system with the relays. Thus, the WPT system with multiple n resonators can be considered as n-1 parts of ...

In this letter, a mode reconfigurable resonator insensitive to its alignment is proposed. The resonator is capable of maintaining a wireless power transmission (WPT) efficiency without degradation of its performance caused by misalignments. After optimum mode selection, the average WPT efficiency of 66.71% (59.02 to 71.34%) in the azimuthal plane is measured at the transmitting distance of 20 cm. The result shows that the resonator can maintain a WPT efficiency with less than 12.5% of variation. Therefore, it is expected that the resonator would be a good solution for the practical applications demanding alignment-free in mid-range and high efficiency WPT systems.

A compact dual-band open-end slot antenna using a chip capacitor was proposed for WLAN applications. The dual-band characteristics were obtained by introducing a current bridge path using the capacitor. This antenna achieves not only a simple and miniaturized structure but also omni-directional radiation patterns with appropriate antenna gains and efficiencies. The proposed antenna is suitable to be embedded in mobile handsets for dual-band WLAN systems.

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