Radio frequency (RF) energy transfer and harvesting techniques have recently become alternative methods to power the next-generation wireless networks As this emerging technology enables proactive energy replenishment of wireless devices, it is advantageous in supporting applications with quality-of-service requirements In this paper, we present a comprehensive literature review on the research progresses in wireless networks with RF energy harvesting capability, which is referred to as RF energy harvesting networks (RF-EHNs) First, we present an overview of the RF-EHNs including system architecture, RF energy harvesting techniques, and existing applications Then, we present the background in circuit design as well as the state-of-the-art circuitry implementations and review the communication protocols specially designed for RF-EHNs We also explore various key design issues in the development of RF-EHNs according to the network types, ie, single-hop networks, multiantenna networks, relay networks, and cognitive radio networks Finally, we envision some open research directions

Wireless Networks With RF Energy Harvesting: A Contemporary Survey

Wireless charging is a technology of transmitting power through an air gap to electrical devices for the purpose of energy replenishment. The recent progress in wireless charging techniques and development of commercial products have provided a promising alternative way to address the energy bottleneck of conventionally portable battery-powered devices. However, the incorporation of wireless charging into the existing wireless communication systems also brings along a series of challenging issues with regard to implementation, scheduling, and power management. In this paper, we present a comprehensive overview of wireless charging techniques, the developments in technical standards, and their recent advances in network applications. In particular, with regard to network applications, we review the static charger scheduling strategies, mobile charger dispatch strategies and wireless charger deployment strategies. Additionally, we discuss open issues and challenges in implementing wireless charging technologies. Finally, we envision some practical future network applications of wireless charging.

Wireless Charging Technologies: Fundamentals, Standards, and Network Applications

In this paper, we investigate a low-complexity technique for simultaneous wireless information and energy transfer in multiple-input multiple-output relay channels. The proposed technique exploits the array configuration at the relay node and uses the antenna elements either for conventional decoding or for rectifying (rectennas). In order to keep the complexity low, a dynamic antenna switching between decoding/rectifying is proposed based on the principles of the generalized selection combiner (GSC); the L strongest paths are allocated for decoding while the remaining channel paths for rectifying (and vice versa). The optimal L as well as the allocation strategy that minimizes the outage probability are investigated via theoretical and numerical results. In addition, two performance bounds that provide the optimal performance without the limitation of GSC are proposed by solving a linear programming and a binary knapsack problem, respectively. The proposed technique is extended to scenarios with multi-user interference, where a zero-forcing receiver is used at the relay node; closed-forms expressions for the outage probability are also derived.

A Low Complexity Antenna Switching for Joint Wireless Information and Energy Transfer in MIMO Relay Channels

This paper studies a simultaneous wireless information and power transfer system with a helping relay in wireless body area network, where the relay harvests energy from the radio-frequency signals sent by other nodes, then the relay uses the harvested energy to help transmit energy to the destination and forward information to the source, respectively. Compared with the existing protocols, we propose the dynamic time allocation strategy in this paper. First, based on power splitting (PS) and time switching (TS) transmission protocols, we propose two new transmission protocols, where the transmission time slots are unequal allocation. Then the optimal strategy to achieve the maximum information throughput by solving nonlinear programming problems is presented. And by changing the relay position, the optimal time and power ratios for the best system performance are presented. Finally, the fitting curves of the optimal solutions for different relay positions are plotted. Numerical results show that our proposed optimal strategy can achieve the best throughput performance and the protocol based on TS outperforms slightly than the protocol based on PS.

Wireless Information and Power Transfer to Maximize Information Throughput in WBAN

Smart-fabric interactive-textile systems offer exciting new possibilities, provided that they exhibit sufficient robustness and autonomy to be reliably deployed in critical applications. Textile multiantenna systems, unobtrusively integrated in a professional garment, are key components of such systems, as they set up energy-efficient and stable wireless body-centric communication links. Yet, their functionality may be further extended by exploiting their surface as energy-harvesting platform. Different state-of-the-art energy harvesters are suitable for compact integration onto a textile antenna. We demonstrate this by integrating a power management system, together with multiple diverse scavenging transducers and a storage module, on a well-chosen textile antenna topology. We provide guidelines to ensure that the additional hardware does not affect the textile antenna's performance. Simultaneous scavenging from different energy sources significantly increases the autonomy of a wearable system, in the meanwhile reducing battery size.

Textile Antennas as Hybrid Energy-Harvesting Platforms

In this paper, we identify the spectrum opportunities for radio frequency (RF) energy harvesting through power density measurements from 350 MHz to 3 GHz. The field trials have been performed in Covilha by using the NAKDA-SMR spectrum analyser with a measuring antenna. Based on the identification of the most promising opportunities, a dual-band band printed antenna operating at GSM bands (900/1800) is proposed, with gains of the order 1.8-2.06 dBi and efficiency 77.6-84%. Guidelines for the design of RF energy harvesting circuits and choice of textile materials for a wearable antenna are also discussed. Besides, we address the guidelines for designing circuits to harvest energy in a scenario where a wireless body area network (WBAN) is being sustained by a TX91501 Powercasf® RF dedicated transmitter and a five-stage Dickson voltage multiplier responsible for harvesting the RF energy. The IRIS motes, considered for our WBAN scenario, can perpetually operate if the RF received power attains at least -10 dBm.

Antennas and circuits for ambient RF energy harvesting in wireless body area networks

This paper presents spectrum opportunities for radio frequency (RF) energy harvesting identified through power density measurements from 350 MHz to 3 GHz. The field trials have been performed in two different cities (Covilha and Lisbon), by using the NARDA-SMR spectrum analyser with measuring antenna, and the Signal Hound spectrum analysers, respectively. The scope of our research considers RF energy harvesting devices, enabling to convert RF energy to direct current (DC), providing an alternative source to power supply wireless sensor network (WSN) devices. Printed antennas, able to operate at GSM (900/1800) bands, are proposed with gains of the order of 1.8-2.06 dBi and efficiency 77.6-84%. Guidelines for the choice of textile materials for a wearable antenna are also provided.

Spectrum opportunities for electromagnetic energy harvesting from 350 mhz to 3 ghz

Radio frequency (RF) energy harvesting is an emerging technology that will enable to drive the next generation of wireless sensor networks (WSNs) without the need of using batteries. In this paper, we present RF energy harvesting circuits specifically developed for GSM bands (900/1800) and a wearable dual-band antenna suitable for possible implementation within clothes for body worn applications. Besides, we address the development and experimental characterization of three different prototypes of a five-stage Dickson voltage multiplier (with match impedance circuit) responsible for harvesting the RF energy. Different printed circuit board (PCB) fabrication techniques to produce the prototypes result in different values of conversion efficiency. Therefore, we conclude that if the PCB fabrication is achieved by means of a rigorous control in the photo-positive method and chemical bath procedure applied to the PCB it allows for attaining better values for the conversion efficiency. All three prototypes (1, 2 and 3) can power supply the IRIS sensor node for RF received powers of -4 dBm, -6 dBm and -5 dBm, and conversion efficiencies of 20, 32 and 26%, respectively.

Design and evaluation of multi-band RF energy harvesting circuits and antennas for WSNs

Field trials have been performed in Covilha to identify the spectrum opportunities for radio frequency (RF) energy harvesting through power density measurements from 350 MHz to 3 GHz. Based on the identification of the most promising opportunities, a dual-band printed antenna was conceived, operating at GSM bands (900/1800), with gains of 1.8 and 2.06 dBi, and efficiency varying from 77.6 to 82%, for the highest and lowest operating frequency bands, respectively. In this paper, guidelines for the design of RF energy harvesting circuits and choice of textile materials for a wearable antenna are briefly discussed. Besides, we address the development and experimental characterization of three different prototypes of a five-stage Dickson voltage multiplier (with and without impedance matching circuit) responsible for RF energy harvesting. All the three prototypes (1, 2 and 3) can power supply the sensor node for RF received powers of 2 dBm, -3 dBm and -4 dBm, and conversion efficiencies of 6, 18 and 20%, respectively.

Henrique M. Saraiva

Papers

Antennas and circuits for ambient RF energy harvesting in wireless body area networks

Spectrum opportunities for electromagnetic energy harvesting from 350 mhz to 3 ghz

Design and evaluation of multi-band RF energy harvesting circuits and antennas for WSNs

Experimental Characterization of Wearable Antennas and Circuits for RF Energy Harvesting in WBANs