Wireless power transfer (WPT) has a long history of over 100 years since the first experiment conducted by Nicola Tesla. However, the most interesting innovation of WPT was born in the 21 ^st century. In this decade, near-field WPT commercialization was advanced, and we now use many near-field WPT products, such as wireless chargers for mobile phones and electric vehicles. In the next decade, we can expect the development of far-field WPT via microwaves, through which we can drive Internet of Things (IoT) sensors without batteries based on transmitted or ambient microwave power. We can charge mobile phones with microwave power. When we focus microwave power on a target by beam forming technology, we can transmit higher wireless power to fly drones or from space to the earth. In conjunction with the research & development of microwave-based WPT, radio regulations suitable for each country need to be discussed. In this paper, I review the history, innovation, and status of the radio regulations of WPT via microwaves with the classification of wide-beam WPT, including harvesting, and narrow-beam WPT.

Power beaming is the efficient point-to-point transfer of electrical energy across free space by a directive electromagnetic beam. This paper clarifies the basic principles of power beaming in simple terms, and proposes a benchmarking methodology for improving the comparative assessment of power beaming systems and technology. An in-depth historical overview tracing the worldwide progress in microwave and millimeter wave (mmWave) experimental demonstrations over the past 60 years shows clear evidence of a significant increase in activity during the last 5 years. In addition, a review of progress in scalable rectenna arrays for the reception of microwave power beaming shows sufficient maturity for new research to initiate on the ruggedization, productization, and system integration aspects of the technology. A review of regulatory issues including spectrum management and safety indicates the need for additional technical solutions and international coordination. Breaking results reported in this paper include 1) data from the first in-orbit flight test of a solar-to-RF “sandwich module”, 2) the construction of multiple US in-orbit demonstrations, planned for 2023 launch, that will demonstrate key technologies for space-based solar power, and 3) a 100-kW mmWave power beaming transmitter demonstrating inherent human life safety.

Wireless power transfer (WPT) technology gained wide recognition over a decade ago following a resonance coupling WPT study conducted by a group at the Massachusetts Institute of Technology (MIT) [1]. WPT was originally proposed by Nicola Tesla at the end of the 19th century [2] based on a study of near-field inductive-coupling WPT and far-field WPT via radio waves. The first patent involving inductive WPT as a wireless charging system was granted in 1894 for the earliest electric vehicle (EV) [3]. Inductive WPT technology is based on a transformer and was commercialized as a wireless charger for an electric toothbrush in 1981 by Panasonic Corporation and as a power source for an integrated circuit (IC) card in 1995 by Sony Corporation. Daifuku Corporation produces many systems for material handling in stockroom and clean room applications [4]. From the 1970s through the 1990s, several research projects on wireless chargers for EVs were undertaken in New Zealand, the United States, and Europe. Advances in microwave technology led to improvements in WPT via radio waves, with many field experiments on microwave power transfer (MPT) conducted from the 1960s through the 1970s by William C. Brown in the United States [4]. The commercialization of RFID at the 920-MHz band started recently, and the proliferation of mobile rechargeable batteries since 2010 accentuates the need for a wireless charger in, e.g., mobile phones, EVs, and sensors for the Internet of Things (IoT).

Radio frequency (RF) energy harvesting and wireless power transmission (WPT) technologies —both near-field and far-field—have attracted significant interest for wireless applications and RFID systems. We already utilize near-field WPT products in our life and it is expected that RF EH and far-field WPT systems can drive the future low-power wireless systems. In this article, we initially present a brief historical overview of these technologies. The main technical challenges of rectennas and WPT transmitters are discussed. Furthermore, this paper presents the recent advances on the development of these technologies, including the possibility of powering RFID systems through the millimeter wave power from 5G networks, the trends in flexible rectennas design and the technological developments on the simultaneous wireless information and power transfer (SWIPT).

We build a phased array system with four power-variable phase-controlled magnetrons (PCMs) by applying the injection-locking method and phase-locked-loop method. To reduce the cost and ensure the durability of the phased array, a waveguide slot array antenna was designed and used for the output antenna of power-variable PCMs. The slot antenna has an expected angle deflection of 22.5°, a gain of 24.9 dBi, and the half bandwidth of the main lobe was 10°. We demonstrated the properties of microwave beamforming and wireless power transfer based on the magnetron phased array system. In horizontal directions, a beam scanning range of ±3° was obtained by adjusting the output phase of the magnetrons. Furthermore, the received dc power reaches 142 W at a distance of 5 m when the output microwave power of the magnetron phased array is 1304 W.