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/cm 2 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.
This paper introduces a novel compact ultralightweight multiband RF energy harvester fabricated on a paper substrate. The proposed rectenna is designed to operate in all recently released LTE bands ...(range 0.79-0.96 GHz; 1.71-2.17 GHz; and 2.5-2.69 GHz). High compactness and ease of integration between antenna and rectifier are achieved by using a topology of nested annular slots. The proposed rectifier features an RF-to-dc conversion efficiency in the range of 5%-16% for an available input power of -20 dBm in all bands of interest, which increases up to 11%-30% at -15 dBm. The rectenna has been finally tested both in laboratory and in realistic scenarios featuring a superior performance to other state-of-the-art RF harvesters on flexible substrates.
Ambient RF energy harvesting is a potential energy source for low-power and battery-less wireless sensors, enabling a range of applications from monitoring to security as part of the ...Internet-of-Things (IoT) scenario. One of the main challenges of ambient RF energy harvesting is the requirement of operation over a multitude of frequency bands of low ambient power densities resulting in a very wide aggregate operating bandwidth. In this paper, design examples of novel ultra-wideband energy harvesters are demonstrated with octave and decade bandwidths in the UHF and low microwave spectrum. The RF-dc conversion efficiency is maximized by tailoring the dimensions of a nonuniform transmission line used to provide broadband impedance matching. The design challenges in terms of impedance matching based on the Bode-Fano theoretical limit, losses and miniaturization are highlighted. Two prototypes are presented and their performance is evaluated. The octave band rectifier showed a measured RF-dc conversion efficiency of more than 60% over a frequency band of 470 to 860 MHz at 10-dBm input power. The decade band rectifier fabricated on Kapton substrate using inkjet printing featured a higher than 33% efficiency over a frequency band from 250 MHz to 3 GHz at 10-dBm input power.
In this work, the concept of dual-band resistance compression networks is introduced and applied to the design of rectifier circuits with improved performance. The use of resistance compression ...networks (RCNs) minimizes the sensitivity of rectifier circuits to variations in the surrounding environment, such as input power level and changes in the rectifier load. The proposed dual-band RCN can be used as the matching network located between the antenna and the rectifying element of a dual-band rectifier for energy harvesting applications. A dual-band ( 915 MHz /2.45 GHz) rectifier based on RCN is designed and characterized showing improved performance in comparison with a conventional dual-band envelope detector by exhibiting improved RF-dc conversion efficiency and reduced sensitivity versus output load and input power variations.
A new electrically small antenna with size ka = 0.415 is presented, fabricated and measured in this work. This is intrinsically matched to 50 Ω, has omni-directional and linear-polarized radiation ...pattern in the horizontal plane with maximum directivity of 1.75 dBi and simulated radiation efficiency of 93%. The antenna in combination with a low-complex and co-planar rectifier with one single diode forms a high efficient and sensitive electrically small rectenna with ka = 0.53 at 868 MHz (UHF RFID-band in Europe). The latter has measured efficiency 22.5% for -19 dBm power input and sensitivity of -44 dBm (or equivalently 0.00028 μW/cm
power density), while at 2.25 μW/cm
is able to supply continuously, i.e., without a boost converter or use of any energy tank, a small electrical device with 118 μW. In order to increase the dc output voltage and the delivered dc power to the load for lower power density levels, rectenna-array configuration is exploited. Application to batteryless, backscatter wireless sensor node powering is discussed. Specifically, for a power density of 0.1237 μW/cm
the RF energy harvesting system delivers 172 μW at 2.85 V every 22.5 s.
Backscatter communication is an emerging paradigm for pervasive connectivity of low-power communication devices. Wirelessly powered backscattering wireless sensor networks (WSNs) become particularly ...important to meet the upcoming era of the Internet of Things (IoT), which requires the massive deployment of self-sustainable and maintenance-free low-cost sensing and communication devices. This article will introduce the state-of-the-art antenna design and radio frequency (RF) system integration for wirelessly powered backscatter communications, covering both the node and the base unit. We capture the latest development in ultralow-power RF front ends and coding schemes for <inline-formula> <tex-math notation="LaTeX">\mu \text{W} </tex-math></inline-formula>-level backscatter modulators, as well as the latest progress in wireless power transfer (WPT) and energy harvesting (EH) techniques. Newly emerged rectenna system, waveform design, and channel optimization are reviewed in light of the opportunities for adaptively optimizing the WPT/EH efficiency for low-power signals with varying conditions. In addition, advanced device packaging and integration technologies in, e.g., additively manufactured RF components and modules for microwave and millimeter-wave ubiquitous sensing and backscattering energy-autonomous RF structures are reported. Inkjet printing for the sustainable and ultralow-cost fabrication of flexible RF devices and sensors will be reviewed to provide a prospective insight into the future packaging of backscatter communications from the chip-level design to complete system integration. Finally, this article will also address the challenges in fully wireless powered backscatter radio networks and discuss the future directions of backscatter communication in terms of "Green IoT" and "Low Carbon" smart home, smart city, smart skin, and machine-to-machine (M2M) applications.
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 (λ 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 Ω.
Wettability is one of the key controlling parameters for multiphase flow in porous media, and paramount for various geoscience applications. While a general awareness of the importance of wettability ...was established decades ago, our fundamental understanding of how wettability influences transport and of how to characterize wettability has improved tremendously in recent years through breakthroughs in imaging technology and modeling techniques. Numerical modeling studies clearly show not only that macroscopic two-phase flow is influenced by the average wettability, but also that the spatial distribution of wetting significantly impacts the macroscopic parameters. Herein, we explore the thermodynamics for porous multiphase systems, and recent breakthroughs in wettability characterization. Our view is that bridging the multiscale characterization of wetting must consider two fundamental perspectives: geometry and energy. Advancing the overall description requires an improved understanding of the operative mechanisms that dominate at various scales, and the development of quantitative approaches to capture these effects. We take a multistage approach, looking at these fundamental perspectives from the sub-pore-to-pore length scales, followed by the pore-to-core length scales using various analytical techniques and numerical simulations. Within this context, there remain many open-ended questions, and we therefore highlight these issues to provide guidance on future research directions. Our overall aim is to provide comprehensive guidance on the multiscale characterization of wettability in porous media, in order to facilitate novel research.
Interfacial tension measurements are reported for the (H2O + CO2) system at pressures of (1 to 60) MPa and temperatures of (298 to 374) K. The pendant drop method was implemented using a ...high-pressure apparatus consisting of a view cell, fitted with a high-pressure capillary tube for creating pendant H2O drops in the CO2 bulk phase. The reported results have a relative standard deviation in most cases of less than 1.0 % and are in good agreement with literature values at low pressures. However, at higher pressures (up to 45 MPa), there is a significant scatter in the published data; the reasons for this are discussed. Measurements in the present work extend the pressure range of available data up to pressures of 60 MPa.
In this paper, the far-field energy harvesting system for self-sustainable wireless autonomous sensor application is presented. The proposed autonomous sensor system consists of a wireless power ...supplier (active antenna) and far-field energy harvesting technology-enabled autonomous battery-less sensors. The wireless power supplier converts solar power to electromagnetic power in order to transfer power to multiple autonomous sensors wirelessly. The autonomous sensors have far-field energy harvesters which convert transmitted RF power to voltage regulated DC power to power-on the sensor system. The hybrid printing technology was chosen to build the autonomous sensors and the wireless power suppliers. Two popular hybrid electronics technologies (direct nano-particle printing and indirect copper thin film printing techniques) are discussed in detail.
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