Research on wireless power transmission by a rectenna using millimeter waves and subterahertz waves is gaining attention. It is expected that energy harvesters at high frequencies will be developed for use with future 5 G. High-power wireless power supply to various applications will be possible because of miniaturization of the rectenna. As described herein, we investigate earlier studies of millimeter-wave wireless power supply, selecting and explaining salient examples of millimeter-wave high power wireless power supply.

New small unmanned air vehicles designated as micro air vehicles (MAVs) are increasingly attractive for research, environmental observation, and commercial purposes. As described herein, the feasibility of a system for wireless power transmission via microwaves for MAVs was investigated. For its light weight and flexibility, a textile-based rectenna was proposed for microwave wireless power transmission of MAVs. To investigate bending effects on radiation performance, a microstrip patch antenna with a 5.8 GHz left-hand circular polarization was developed on a textile substrate. The antenna return loss, 20 dB, increased slightly with the antenna bending angle. An axial ratio <3 dB was maintained when the antenna bend angle was <30°. A rectification circuit was formed on the back side felt with sandwiched copper foil as a ground plate. Its weight per unit area was 0.08 g/m2, with maximum rectification efficiency of 58% with 100 Ω load at 63 mW input power. The average and maximum total transmission efficiency using the 5.8 GHz multiple rectenna with a 2.45 GHz retrodirective system were, respectively, 0.44 and 0.60%. The possibility and feasibility of microwave power transmission system using the textile-based rectenna were evaluated.

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An adaptive calibration technique of timing skew mismatch in time-interleaved analog-todigital converters Review of Scientific Instruments 90, 025102 (2019);