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

http://ieeexplore.ieee.org/iel5/5610941/5624686/05624745.pdf

Power electronics

Substrate-integrated waveguide (SIW) technology represents an emerging and very promising candidate for the development of circuits and components operating in the microwave and millimetre-wave region. SIW structures are generally fabricated by using two rows of conducting cylinders or slots embedded in a dielectric substrate that connects two parallel metal plates, and permit the implementation of classical rectangular waveguide components in planar form, along with printed circuitry, active devices and antennas. This study aims to provide an overview of the recent advances in the modelling, design and technological implementation of SIW structures and components.

Review of substrate-integrated waveguide circuits and antennas

Advances in wireless technologies, low-power electronics, the internet of things, and in the domain of connected health are driving innovations in wearable medical devices at a tremendous pace. Wearable sensor systems composed of flexible and stretchable materials have the potential to better interface to the human skin, whereas silicon-based electronics are extremely efficient in sensor data processing and transmission. Therefore, flexible and stretchable sensors combined with low-power silicon-based electronics are a viable and efficient approach for medical monitoring. Flexible medical devices designed for monitoring human vital signs, such as body temperature, heart rate, respiration rate, blood pressure, pulse oxygenation, and blood glucose have applications in both fitness monitoring and medical diagnostics. As a review of the latest development in flexible and wearable human vitals sensors, the essential components required for vitals sensors are outlined and discussed here, including the reported sensor systems, sensing mechanisms, sensor fabrication, power, and data processing requirements.

Monitoring of Vital Signs with Flexible and Wearable Medical Devices

RF harvesting circuits have been demonstrated for more than 50 years, but only a few have been able to harvest energy from freely available ambient (i.e., non-dedicated) RF sources. In this paper, our objectives were to realize harvester operation at typical ambient RF power levels found within urban and semi-urban environments. To explore the potential for ambient RF energy harvesting, a city-wide RF spectral survey was undertaken from outside all of the 270 London Underground stations at street level. Using the results from this survey, four harvesters (comprising antenna, impedance-matching network, rectifier, maximum power point tracking interface, and storage element) were designed to cover four frequency bands from the largest RF contributors (DTV, GSM900, GSM1800, and 3G) within the ultrahigh frequency (0.3-3 GHz) part of the frequency spectrum. Prototypes were designed and fabricated for each band. The overall end-to-end efficiency of the prototypes using realistic input RF power sources is measured; with our first GSM900 prototype giving an efficiency of 40%. Approximately half of the London Underground stations were found to be suitable locations for harvesting ambient RF energy using our four prototypes. Furthermore, multiband array architectures were designed and fabricated to provide a broader freedom of operation. Finally, an output dc power density comparison was made between all the ambient RF energy harvesters, as well as alternative energy harvesting technologies, and for the first time, it is shown that ambient RF harvesting can be competitive with the other technologies.

Ambient RF Energy Harvesting in Urban and Semi-Urban Environments

In this paper, various ambient energy-harvesting technologies (solar, thermal, wireless, and piezoelectric) are reviewed in detail and their applicability in the development of self-sustaining wireless platforms is discussed. Specifically, far-field low-power-density energy-harvesting technology is thoroughly investigated and a benchmarking prototype of an embedded microcontroller-enabled sensor platform has been successfully powered by an ambient ultrahigh-frequency (UHF) digital TV signal (512-566 MHz) where a broadcasting antenna is 6.3 km away from the proposed wireless energy-harvesting device. A high-efficiency dual-band ambient energy harvester at 915 MHz and 2.45 GHz and an energy harvester for on-body application at 460 MHz are also presented to verify the capabilities of ambient UHF/RF energy harvesting as an enabling technology for Internet of Things and smart skins applications.

http://users.ece.gatech.edu/etentze/Procs14_Sangkil.pdf

Ambient RF Energy-Harvesting Technologies for Self-Sustainable Standalone Wireless Sensor Platforms

In this paper, various ambient energy-harvesting technologies (solar, thermal, wireless, and piezoelectric) are reviewed in detail and their applicability in the development of self-sustaining wireless platforms is discussed. Specifically, far- field low-power-density energy-harvesting technology is thor- oughly investigated and a benchmarking prototype of an embedded microcontroller-enabled sensor platform has been successfully powered by an ambient ultrahigh-frequency (UHF) digital TV signal (512-566 MHz) where a broadcasting antenna is 6.3 km away from the proposed wireless energy-harvesting device. A high-efficiency dual-band ambient energy harvester at 915 MHz and 2.45 GHz and an energy harvester for on-body application at 460 MHz are also presented to verify the capa- bilities of ambient UHF/RF energy harvesting as an enabling technology for Internet of Things and smart skins applications.

Ambient RF Energy-Harvesting Technologies for Self-Sustainable Standalone Wireless Sensor Platforms This paper presents various ambient energy-harvesting technologies and investigates their applicability in the development of self-sustaining wireless platforms.

This paper presents the design of a cost effective, hybrid energy harvesting circuit combining a solar cell and a rectenna capable to harvest ambient electromagnetic energy. Electromagnetic analysis is used to model and optimize the designed circuits in order to allow the antenna and solar cell to share the same area leading to a compact structure. Nonlinear harmonic balance optimization is used to maximize the RF-to-DC conversion efficiency of the rectenna circuitry in the presence of the solar cell and both wideband and multiband topologies are presented. Furthermore, a low cost and flexible polyethylene terephthalate PET substrate and a flexible amorphous silicon solar cell are chosen, providing for both a low cost and conformal structure. A prototype able to generate a maximum DC power of 56 mW when the solar cell is illuminated with 100 mW/cm2 solar irradiance, and a dual band rectenna demonstrating an efficiency of 15% around 850 MHz and 1850 MHz when illuminated by a microwave signal of available power is presented.

Conformal Hybrid Solar and Electromagnetic (EM) Energy Harvesting Rectenna

A compact dual-band rectenna operating at 915 MHz and 2.45 GHz is presented. The rectenna consists of a slot-loaded dual-band folded dipole antenna and a dual-band rectifier. The length of the proposed antenna is only 36.6% of the half-wavelength $(\lambda_{0}/2)$ dipole antenna at 915 MHz while keeping dual-band property at 915 MHz and 2.45 GHz. The rectifier circuit is optimized for low input power densities using harmonic balance (HB) simulation. The efficiencies of the rectifier are evaluated with both single- and dual-frequency input signals. The measured results show an efficiency of 37% and 30% at 915 MHz and at 2.45 GHz when illuminated by a microwave signal of available power of $-$ 9 dBm for a load resistor of 2.2 k $\Omega$ .

A Compact Dual-Band Rectenna Using Slot-Loaded Dual Band Folded Dipole Antenna

A rectenna design methodology combining electromagnetic (EM) simulation and harmonic balance (HB) analysis is presented. It consists of applying reciprocity theory to calculate the Thevenin equivalent circuit of the receiving antenna and optimizing the rectifying circuit parameters using HB analysis. The method is demonstrated by designing a 2.45-GHz rectenna based on a square aperture-coupled patch antenna with dual linear polarization. A compact implementation is achieved by etching a cross-shaped slot on the patch surface leading to a 32.5% patch side reduction. Voltage-doubling circuits convert the received RF power from each port to dc permitting the rectenna to receive arbitrarily polarized signals. The circuit is optimized for low input power densities and a simulated maximum efficiency of 38.2% was obtained for 1.5 nWcm-2 input RF power density at 2.43 GHz.

Ana Collado

Papers

Ambient RF Energy-Harvesting Technologies for Self-Sustainable Standalone Wireless Sensor Platforms

Ambient RF Energy-Harvesting Technologies for Self-Sustainable Standalone Wireless Sensor Platforms This paper presents various ambient energy-harvesting technologies and investigates their applicability in the development of self-sustaining wireless platforms.

Conformal Hybrid Solar and Electromagnetic (EM) Energy Harvesting Rectenna

A Compact Dual-Band Rectenna Using Slot-Loaded Dual Band Folded Dipole Antenna

Rectenna design and optimization using reciprocity theory and harmonic balance analysis for electromagnetic (EM) energy harvesting