Table of Content

    25 June 2022, Volume 20 Issue 2
    Special Topic
    Editorial: Special Topic on Simultaneous Wireless Information and Power Transfer: Technology and Practice
    2022, 20(2):  1-2.  doi:10.12142/ZTECOM.202202001
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    High-Power Simultaneous Wireless Information and Power Transfer: Injection-Locked Magnetron Technology
    YANG Bo, MITANI Tomohiko, SHINOHARA Naoki, ZHANG Huaiqing
    2022, 20(2):  3-12.  doi:10.12142/ZTECOM.202202002
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    Applications using simultaneous wireless information and power transfer (SWIPT) have increased significantly. Wireless communication technologies can be combined with the Internet of Things to develop many innovative applications using SWIPT, which is mainly based on wireless energy harvesting from electromagnetic waves used in communications. Wireless power transfer that uses magnetrons has been developed for communication technologies. Injection-locked magnetrons that can be used to facilitate high-power SWIPT for several devices are reviewed in this paper. This new technology is expected to pave the way for promoting the application of SWIPT in a wide range of fields.

    An Overview of SWIPT Circuits and Systems
    TORRES Ricardo, MATOS Diogo, PEREIRA Felisberto, CORREIA Ricardo, CARVALHO Nuno Borges
    2022, 20(2):  13-18.  doi:10.12142/ZTECOM.202202003
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    From a circuit implementation perspective, this paper presents a brief overview of simultaneous wireless information and power transmission (SWIPT). By using zero-power batteryless wireless sensors, SWIPT mixes wireless power transmission with wireless communications to allow the truly practical implementation of the Internet of Things as well as many other applications. In this paper, technical backgrounds, problem formation, state-of-the-art solutions, circuit implementation examples, and system integrations of SWIPT are presented.

    Optimal Design of Wireless Power Transmission Systems Using Antenna Arrays
    SUN Shuyi, WEN Geyi
    2022, 20(2):  19-27.  doi:10.12142/ZTECOM.202202004
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    Three design methods for wireless power transmission (WPT) systems using antenna arrays have been investigated. The three methods, corresponding to three common application scenarios of WPT systems, are based on the method of maximum power transmission efficiency (MMPTE) between two antenna arrays. They are unconstrained MMPTE, weighted MMPTE, and constrained MMPTE. To demonstrate the optimal design process with the three methods, a WPT system operating at 2.45 GHz is designed, simulated, and fabricated, in which the transmitting (Tx) array, consisting of 36 microstrip patch elements, is configured as a square and the receiving (Rx) array, consisting of 5 patch elements, is configured as anL shape. The power transmission efficiency (PTE) is then maximized for the three application scenarios, which yields the maximum possible PTEs and the optimized distributions of excitations for both Tx and Rx arrays. The feeding networks are then built based on the optimized distributions of excitations. Simulations and experiments reveal that the unconstrained MMPTE, which corresponds to the application scenario where no radiation pattern shaping is involved, yields the highest PTE. The next highest PTE belongs to the weighted MMPTE, where the power levels at all the receiving elements are imposed to be equal. The constrained MMPTE has the lowest PTE, corresponding to the scenario in which the radiated power pattern is assumed to be flat along with the Rx array.

    Dynamic Power Transmission Using Common RF Feeder with Dual Supply
    DUONG Quang‑Thang, VO Quoc‑Trinh, PHAN Thuy‑Phuong, OKADA Minoru
    2022, 20(2):  28-36.  doi:10.12142/ZTECOM.202202005
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    This paper proposes the design concept of a dynamic charging system for electric vehicles using multiple transmitter coils connected to a common radio frequency (RF) feeder driven by a pair of two power supplies. Using a common RF feeder for multiple transmitter coils reduces the power electronic redundancy compared to a conventional system, where each transmitter coil is individually driven by one switched-mode power supply. Currently, wireless charging of electric vehicles is recommended to operate in the frequency range of 85 kHz and beyond. In this frequency range, the signal wavelength is shorter than about 3.5 km. Therefore, a charging pad longer than several hundred meters is subject to the standing wave effect. In such a case, the voltage significantly varies along the RF feeder, resulting in a variation in the received power level when the receiver moves. Specifically, the received power significantly deteriorates when the receiver is nearby a node of the voltage standing wave. In this paper, we employ a pair of two power sources which are electrically separated by an odd-integer number of the quarter wavelength to drive the RF feeder. As a result, the voltage standing wave generated by one power source is complemented by that of the other, leading to stable received power and transmission efficiency at all the receiver’s positions along with the charging pad. Simulation results at the 85 kHz frequency band verify the output power stabilization effect of the proposed design. It is worth noting that the proposed concept can also be applied to simultaneous wireless information and power transfer (SWIPT) for passive radio frequency identification (RFID) tags by raising the operation frequency to higher industrial, scientific and medical (ISM) bands, e.g., 13.56 MHz and employing similar modulation methods as in the current RFID technology.

    Polarization Reconfigurable Patch Antenna for Wireless Power Transfer Related Applications
    SHEN Jun, ZHAO Tianxiang, LIU Xueguan
    2022, 20(2):  37-42.  doi:10.12142/ZTECOM.202202006
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    A polarized reconfigurable patch antenna is proposed in this paper. The proposed antenna is a dual cross-polarized patch antenna with a programmable power divider. The programmable power divider consists of two branch line couplers (BLC) and a digital phase shifter. By adjusting the phase of the phase shifter, the power ratio of the power divider can be changed, and thus the feed power to the antenna input port can be changed to reconfigure the antenna polarization. The phase-controlled power divider and the cross dual-polarized antenna are designed, fabricated and tested, and then they are combined to realize the polarized reconfigurable antenna. By moving the phase of the phase shifter, the antenna polarization is reconfigured into vertical polarization (VP), horizontal polarization (HP), and circular polarization (CP). The test is conducted at the frequency of 915 MHz, which is widely used for simultaneous wireless information and power transfer (SWIPT) in radio-frequency identification (RFID) applications. The results demonstrate that when the antenna is configured as CP, the axial ratio of the antenna is less than 3 dB, and when the antenna is configured as HP or VP, the axial ratio of the antenna exceeds 20 dB. Finally, experiments are conducted to verify the influence of antenna polarization changes on wireless power transmitting. As expected, the reconfigured antenna polarization can help improve the power transmitting efficiency.

    A Radio‑Frequency Loop Resonator for Short‑Range Wireless Power Transmission
    WANG Xin, LI Wenbo, LU Mingyu
    2022, 20(2):  43-47.  doi:10.12142/ZTECOM.202202007
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    A microstrip loop resonator loaded with a lumped capacitor is proposed for short-range wireless power transmission applications. The overall physical dimensions of the proposed loop resonator configuration are as small as 3 cm by 3 cm. Power transmission efficiency of greater than 80% is achieved with a power transmission distance smaller than 5 mm via the strong coupling between two loop resonators around 1 GHz, as demonstrated by simulations and measurements. Experimental results also show that the power transmission performance is insensitive to various geometrical misalignments. The numerical and experimental results of this paper reveal a bandwidth of more than 50 MHz within which the power transmission efficiency is above 80%. As a result, the proposed microstrip loop resonator has the potential to accomplish efficient wireless power transmission and high-speed (higher than 10 Mbit/s) wireless communication simultaneously.

    Programmable Metasurface for Simultaneously Wireless Information and Power Transfer System
    CHANG Mingyang, HAN Jiaqi, MA Xiangjin, XUE Hao, WU Xiaonan, LI Long, CUI Tiejun
    2022, 20(2):  48-62.  doi:10.12142/ZTECOM.202202008
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    Implementing self-sustainable wireless communication systems is urgent and challenging for 5G and 6G technologies. In this paper, we elaborate on a system solution using the programmable metasurface (PMS) for simultaneous wireless information and power transfers (SWIPT), offering an optimized wireless energy management network. Both transmitting and receiving sides of the proposed solution are presented in detail. On the transmitting side, employing the wireless power transfer (WPT) technique, we present versatile power conveying strategies for near-field or far-field targets, single or multiple targets, and equal or unequal power targets. On the receiving side, utilizing the wireless energy harvesting (WEH) technique, we report our work on multi-functional rectifying metasurfaces that collect the wirelessly transmitted energy and the ambient energy. More importantly, a numerical model based on the plane-wave angular spectrum method is investigated to accurately calculate the radiation fields of PMS in the Fresnel and Fraunhofer regions. With this model, the efficiencies of WPT between the transmitter and the receiver are analyzed. Finally, future research directions are discussed, and integrated PMS for wireless information and wireless power is outlined.