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J. Electromagn. Eng. Sci > Volume 10(4); 2010 > Article
Journal of the Korean Institute of Electromagnetic and Science 2010;10(4):224-230.
DOI: https://doi.org/10.5515/JKIEES.2010.10.4.224   
Beam Efficiency of Wireless Power Transmission via Radio Waves from Short Range to Long Range
Naoki Shinohara
Department of Research Institute for Sustainable Humanosphere, Kyoto University
Wireless power transmission (WPT) is useful technology in near future. There are some kinds of the WPT technologies, WPT via radio waves, resonance coupling, and inductive. Especially the WPT via radio waves is used for multi-purposes from short range to long range application. However, unfortunately it is misunderstood that it is low efficiency and low power. In this paper, I show the theory of beam efficiency between transmitting antennas and receiving antennas and also show some high efficient applications of the WPT via radio waves. Especially, I pick up a wireless power charging system of an electric vehicle and show the experimental results. I show difference between the theory of beam efficiency and the experimental results of short range WPT. I indicate that reasons of poor beam efficiency in the experiment are (1) change of impedance caused by mutual coupling between transmitting antennas and receiving antennas, (2) oblique direction of microwave power to receiving antennas caused by short distance.
Key words: Wireless Power Transmission, Microwave, Beam Efficiency, Electric Vehicle


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