Microwave Power Transfer System Research Articles

Implementation of Digital Beamforming System for Microwave Power Transfer With Real-Time Beam Scanning

In this study, we propose a digital beamforming system for microwave power transfer with a real-time beam-scanning algorithm for tracking a moving receiver. To perform scanning, each channel in the transmitter generates and converts a baseband signal for the allocated beam direction based on the pilot slots in a frame structure. An initial timer reset process and a preamble are included in the algorithm to maintain time synchronization among units of the scanning period in a wireless environment. The average received power is simulated, and the optimal frame configuration is derived by considering the proportion of an energy transmission slot in the frame. For experimental verification, we design a 4 × 4 digital beamforming system operating at 5.8 GHz and a receiver. The scanning performance is experimentally validated with various numbers of scanning beams and placements of the receiver. Moreover, when radiating 16 W of RF power, an RF power of 100 mW or more is received in all sections for the scenario of the receiver moving in a 1 m distance using 1 second period beam scanning. The proposed microwave power transfer system with a real-time beam scanning algorithm is verified to track the moving receiver in a wireless environment and perform optimal microwave power transfer.

Multiple Beamforming Using Multi-Tone Signals for Microwave Power Transfer System

Multiple Beamforming Using Multi-Tone Signals for Microwave Power Transfer System

Efficient microwave power transfer system using retrodirective antenna array

ABSTRACT In this paper, we present a design method for a highly efficient retrodirective array (RDA)-based microwave power transfer (MPT) system for the mMTC scenario, and evaluate its characteristics through experiments. Long-range wireless power transfer is required to effectively support the mMTC situation. RDA-based MPT controls and tracks the power beam towards the device within a certain range and it enables efficient power transfer. The overall link budget analysis is examined first and the required antenna gain is calculated. The required antenna gain can be secured using multiple-antenna modules. So, it is possible to design an RDA-based MPT system. In this paper, we implement a reduced RDA-based MPT system and evaluate its characteristics to confirm the feasibility of this design method. Through experiments, it has been confirmed that additional gain can be secured by using multiple antenna modules, and the RDA function can be effectively operated to effectively make a power beam in the direction of the power receiver. Conclusively, the gain of about 2.2dB increased whenever the number of antennas is doubled. The experimental results also show that the RDA-based MPT system designed in this paper is capable of adaptive power beamforming from −30 degrees to 30 degrees.

Sidelobe Suppression Beamforming Using Tapered Amplitude Distribution for a Microwave Power Transfer System with a Planar Array Antenna

This paper proposes a sidelobe suppression beamforming scheme using tapered amplitude distribution for microwave power transfer (MPT) with a two-dimensional planar array antenna (PAA). To overcome the undesirable effects of sidelobes, the magnitude of the sidelobes can be lowered by manipulating the amplitude distribution of the PAA. By analyzing the array factor of the PAA, we expressed the amplitude distribution as the product of two one-dimensional vectors. Moreover, we developed a method for obtaining these vectors from an expected sidelobe level (SLL). We used the Chebyshev taper, which has a higher directivity than other distributions given an expected SLL, for the amplitude distribution. To verify the proposed method, we designed and implemented a digital beamforming system with a 4 × 4 transmitter (Tx) array and a receiver (Rx) at 5.8 GHz. Compared with a uniform amplitude distribution, the proposed method reduced the SLL by 7.5 dB but the received RF power by only 0.6 dB. We compared the performance of the proposed MPT system with the results of previous studies.

Beamforming Algorithm Based on the Orthogonal Phase Bases With Trigonometric Estimation for Microwave Power Transfer Systems

Microwave power transfer (MPT) has been widely studied, as sensors or mobile/wearable devices have been used, especially for IoT applications. A beamforming algorithm is essential and important for both the performance and the system complexity of MPT systems. In this paper, a beamforming algorithm that requires only 3 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> -2 transmission sequences for the Tx array with <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> elements to estimate the optimum set of the transmission phases is proposed. The proposed algorithm is simply based on trigonometric calculations, and can be directly applied to an MPT system without element calibration. Calculation of the optimum phase set of the Tx only requires the information of the received power level from the Rx. Since simultaneous phase shifting of the multiple elements is performed during the power transmission sequence, it can have a relatively high Rx SNR, compared to the methods based on phase shifting of only one element at each sequence. In addition, optimum transmission phase sets for multiple Rx’s can be obtained from a beamforming procedure using the proposed algorithm, if the received power levels from the multiple Rx’s are collected. For verification of the proposed algorithm, a 5.2 GHz 8×4 Tx array having an output power of 0.5 W per Tx element was implemented. Beamforming experiment was performed using the proposed algorithm. A received power of 45 mW at 2 m distance was achieved, which is very close to the simulated value.

다중 센서 네트워크에 효과적인 전력 공급을 위한 선택적 전파전력전송 시스템

본 논문에서는 다중 센서 네트워크에 효율적으로 무선전력전송을 수행할 수 있는 새로운 MPT(Microwave Power Transfer) 시스템을 제안한다. 제안하는 시스템은 센서의 ID(Identification) 및 배터리 상태 정보를 활용하여 선택적으로 전력 공급이 급한 센서에 우선적으로 전력송신을 한다. 이러한 우선순위 처리 방식을 사용하므로써, 기존의 무작위 선택으로 전력을 전송하는 MPT 시스템이 가지고 있는 단점을 극복할 수 있다. 기존 MPT 시스템에서 전력요청에 따라 무작위로 전력전송을 할 때, 상대적으로 전력 소모가 많으면서 배터리 전력이 낮은 센서가 전력을 제때에 공급받기 어려워진다. 제안하는 시스템은 이러한 문제를 효과적으로 해결할 수 있다. 시뮬레이션을 통하여, 제안하는 MPT 시스템은 다양한 센서 네트워크 환경에서 기존 MPT 시스템과 비교하여, 네트워크 전체적으로 각 센서들이 보다 효과적으로 작업을 수행할 수 있는 환경을 제공할 수 있음을 확인하였다. 특히, 센서의 수에 따라 전력송신기의 파라미터를 조절하면, 최대 약 45% 정도 센서 네트워크의 작업량을 개선할 수 있다.

A Study on Microwave Power Transfer System to High Altitude Platform Station Considering Rectification Efficiency

A Study on Microwave Power Transfer System to High Altitude Platform Station Considering Rectification Efficiency

Indoor Microwave Power Transfer System to Realize Fully True Wireless IoT Devices

近年のIoT デバイス普及に伴い，センシングデータ等の送受信の無線化が進んでいる．一方で電源配線は残るため，配線が困難な箇所( 動く場所・狭い場所・高所等) への設置が難しい．電池を用いることで配置の制約は解消されるものの，ある程度( 平均1 mW 超) の消費電力では電池交換が必要となり，多額の交換コストが発生してしまう．解決手段として，マイクロ波により数m 先のセンサ等デバイスに電力を届けるマイクロ波電力伝送技術が注目を集めている．本論文では数〜 10 m 程度のエリアに対し最大数百mW 程度の電力を送電可能な5.7 GHz 帯を用いたマイクロ波給電システムの紹介を行う

Retroreflective Transceiver Array Using a Novel Calibration Method Based on Optimum Phase Searching

The retrodirective or retroreflective method has been used as a radio-frequency beamforming method for massive antenna array, for wireless communication systems, radars, and microwave power transfer (MPT) systems. In particular, the retroreflective method is suitable for optimum beamforming for both near- and far-field zones. Each transmitter (Tx) and receiver (Rx) circuit in the Tx array has its own phase offset, which should be calibrated for optimum retroreflective operation. This article presents a simple and effective phase offset calibration method for the retroreflective beamforming arrays using a one-by-one basis optimum phase searching method with a receiver at a reference point. To verify the proposed calibration method for a massive retroreflective beamforming array, a 5.2 GHz shortand mid-range (≤4 m) MPT system, including a Tx array based on 8 × 8 antennas and an Rx using six antennas (five rectennas for power reception, and 1 additional for pilot transmission) for charging mobile handsets was designed and implemented. Optimal retroreflective beamforming from the Tx array, which was calibrated using the proposed method, was experimentally verified for elevation angles of within ±45 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sup> for both xz- and yz-planes. The implemented Tx and Rx circuits achieved a received dc power of about 100 mW at a distance of 4 m.

Lateral GaN Schottky Barrier Diode for Wireless High-Power Transfer Application With High RF/DC Conversion Efficiency: From Circuit Construction and Device Technologies to System Demonstration

In this article, we have carried out a comprehensive study on the wireless power transfer (WPT) concept from the rectifier circuit construction and state-of-art GaN Schottky barrier diode (SBD) device technology to the WPT system demonstration. Benefited from the wide bandgap, high mobility, and saturation velocity of the gallium nitride (GaN) two-dimensional electron gas, engineered lateral GaN SBD with low turn-ON voltage (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</sub> ) of 0.47 V, ON-resistance (R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</sub> ) of 4 Ω, breakdown voltage of 170 V, and junction capacitance (C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">j</sub> ) of 0.32 pF at 0 V bias are achieved, which satisfy the fundamental requirements for microwave power rectification. After incorporating the high-performance GaN SBD into the optimized rectifier circuit, high radio frequency (RF)/dc conversion efficiency of 79% is achieved, and the input power of per single GaN SBD is increased by 10X when compared with that of a commercially available silicon (Si) SBD at the same efficiency of 50% and frequency of 2.45 GHz. Based on the rectifier circuit, a microwave power transfer system is constructed with 400 light emitting diodes lighted up, verifying the great promise of adopting high-power GaN SBD for the wireless high-power transfer as an alternative energy-harvesting technique for future WPT application.

Adaptive impedance matching of rectifier for a 100 MHz microwave power transfer system

Microwave power transmission (MPT) has been one of the most promising systems in the far-field wireless power transmission system. In MPT system, the harmonic energy generated by conventional diode rectifying circuit has great impact on the overall efficiency. Moreover, the passive impedance network leads to power reflection, which is the other factor leading to the overall efficiency decline. In this study, a 10 W output 100 MHz two-stage adaptive impedance-matching rectifying circuit is proposed which can make input impedance constant. About 100 MHz belongs to the band of radio frequency (RF) and the conception of microwave. The first-stage rectifier is modelled mathematically, which plays an essential role in constructing the initial input impedance and designing the control method of second-stage converter. By adjusting the duty cycle of the second-stage converter, the impedance of the whole rectifier realises 50 Ω under various input and the output conditions by means of simulations and experiments. The simulation and experimental results are shown to verify the effectiveness of the proposed RF to direct current converter and its control method. The overall efficiency with full load is up to nearly 65%.

Study on a Microwave Power Transfer System to a Stratospheric Platform Airship

Study on a Microwave Power Transfer System to a Stratospheric Platform Airship

Microwave Power Transfer System Design

Microwave Power Transfer System Design

Microwave Power Transfer With Optimal Number of Rectenna Arrays for Midrange Applications

In this letter, the microwave power transfer (MPT) system with the optimal number of rectenna arrays for midrange applications is proposed, theoretically analyzed, and verified. A retrodirective power transmitter is designed to overcome the degradation by the near-field effect and enhance the power transfer efficiency. The implemented transmitter is composed of 16 $\times$ 1 patch antennas with a $\lambda /2$ spacing, and each of the antennas has a circuit for simultaneously detecting and shifting the phase, and operates at a frequency of 2.45 GHz. To further improve the power transfer efficiency, the parallel dc combining rectenna array is designed since the conventional RF combining rectenna has several problems in the case of midrange. The fabricated rectenna array consists of 8 $\times$ 1 rectennas with a $\lambda /2$ spacing and a dc power management circuit. In addition, the optimal number of rectenna arrays is proposed, considering the size of the receiver. In the experiments, the optimal number of rectennas is 3 when the transfer distance is 1 m. The achieved power transfer efficiency from three-arrayed rectennas is 4.47%, while the efficiency of 5.01% is achieved from eight-arrayed rectennas. Experimental results from the implemented MPT system show good agreement with the proposed theory.

Flat-topped beam forming experiment for microwave power transfer system to a vehicle roof

We proposed and examined a microwave power transfer system for electric vehicles (EVs). In this system, electricity is transmitted from a transmitting antenna over an EV to a receiving antenna on the roof of the EV. We used a rectenna to convert the received microwave power to direct current power. The conversion efficiency of a rectenna array is affected by the input power level distribution, and we have to form a flat-topped beam pattern to increase the conversion efficiency. We conducted an experiment to form a flat-topped beam pattern by using a phased array antenna. In this experiment, the output power of each antenna element is uniform and cannot be controlled independently. Hence, we controlled only the output phases of each antenna element and formed a flat-topped beam pattern. The distance between the transmitting antenna and the receiving area is 6.45 m, and the receiving area corresponds to a space in which the azimuth and elevation are in the range of −5°–5°.

A space-to-space microwave wireless power transmission experiential mission using small satellites

A space solar microwave power transfer system (SSMPTS) may represent a paradigm shift to how space missions in Earth orbit are designed. A SSMPTS may allow a smaller receiving surface to be utilized on the receiving craft due to the higher-density power transfer (compared to direct solar flux) from a SSMPTS supplier craft; the receiving system is also more efficient and requires less mass and volume. The SSMPTS approach also increases mission lifetime, as antenna systems do not degrade nearly as quickly as solar panels. The SSMPTS supplier craft (instead) can be replaced as its solar panels degrade, a mechanism for replacing panels can be utilized or the SSMPTS can be maneuvered closer to a subset of consumer spacecraft. SSMPTS can also be utilized to supply power to spacecraft in eclipse and to supply variable amounts of power, based on current mission needs, to power the craft or augment other power systems.A minimal level of orbital demonstrations of SSP technologies have occurred. A mission is planned to demonstrate and characterize the efficacy of space-to-space microwave wireless power transfer. This paper presents an overview of this prospective mission. It then discusses the spacecraft system (comprised of an ESPA/SmallSat-class spacecraft and a 1-U CubeSat), launch options, mission operations and the process of evaluating mission outcomes.