RF energy harvesters for wireless sensors, state of the art, future prospects and challenges: a review

The power consumption of portable gadgets, implantable medical devices (IMDs) and wireless sensor nodes (WSNs) has reduced significantly with the ongoing progression in low-power electronics and the swift advancement in nano and microfabrication. Energy harvesting techniques that extract and convert ambient energy into electrical power have been favored to operate such low-power devices as an alternative to batteries. Due to the expanded availability of radio frequency (RF) energy residue in the surroundings, radio frequency energy harvesters (RFEHs) for low-power devices have garnered notable attention in recent times. This work establishes a review study of RFEHs developed for the utilization of low-power devices. From the modest single band to the complex multiband circuitry, the work reviews state of the art of required circuitry for RFEH that contains a receiving antenna, impedance matching circuit, and an AC-DC rectifier. Furthermore, the advantages and disadvantages associated with various circuit architectures are comprehensively discussed. Moreover, the reported receiving antenna, impedance matching circuit, and an AC-DC rectifier are also compared to draw conclusions towards their implementations in RFEHs for sensors and biomedical devices applications

Design and development of novel radio frequency identification (RFID) tag structures

The objective of the proposed research is to design and develop a series of radio frequency identification (RFID) tag structures that exhibit good performance characteristics with cost optimization and can be realized on flexible substrates such as liquid crystal polymer (LCP), paper-based substrate and magnetic composite material for conformal applications. The demand for flexible RFID tags has recently increased tremendously due to the requirements of automatic identification in various areas. Several major challenges existing in today's RFID technologies need to be addressed before RFID can eventually march into everyone's daily life, such as how to design high performance tag antennas with effective impedance matching for passive RFID IC chips to optimize the power performance, how to fabricate ultra-low-cost RFID tags in order to facilitate mass production, how to integrate sensors with passive RFID tags for pervasive sensing applications, and how to realize battery-free active RFID tags in which changing battery is not longer needed. In this research, different RFID tag designs are realized on flexible substrates. The design techniques presented set the framework for answering these technical challenges for which, the focus will be on RFID tag structure design, characterization and optimization from the perspectives of both costs involved and technical constraints.Ph.D.Committee Chair: Tentzeris, Manos; Committee Member: DeJean, Gerald; Committee Member: Ingram, Mary; Committee Member: Kavadias, Stylianos; Committee Member: Laskar, Jo

A compact low-power EM energy harvester using electrically small loop resonator

Electromagnetic (EM) energy harvester is a combination of an antenna or EM collector and a rectifier circuit. It is a concept that has seen applications in a variety of areas, as its essential purpose is to harvest and reuse the ambient microwave power. Compact system solutions for EM energy harvesting are presented and investigated in this work. The objective of this work is to reduce the size of the EM harvesters and simplify the fabrication process. A new approach to design a compact EM energy harvester which based on the concept of an electrically small square-loop collector, is proposed. Coplanar waveguide (CPW) transmission lines are utilized to build the half-wave rectifier. The input impedance of the rectifier is designed to be equaled to the conjugate of the impedance of the square-loop collector at the operating frequency. This method not only reduces the mismatch loss, but also reduces the overall size and simplifies the complexity of the system. The efficiency and the DC output power of the design are examined with respect to the power density on the EM harvester surface. Measurements demonstrate that the system is efficient to harvest EM energy in a low power density environment and generate a reasonable DC power. The proposed EM energy harvester is compact, easy to fabricate and integrate into other devices, and suitable for different energy harvesting applications. The mechanical flexibility of the proposed compact EM energy harvester is also discussed. The EM energy harvester is redesigned and fabricated on a thin flexible substrate. The performances are measured with respect to frequency in both planar and curvature configurations. The results show that the operating frequencies for both planar and curvature configurations do not vary. Furthermore, the output power of the two configurations at the operating frequency are very close to each other. The proposed flexible EM energy harvester requires a simpler fabrication process and a smaller size when compared to the previous work reported in the literature for EM energy harvesting at 2.45 GHz. A single element of EM energy harvester is insufficient for powering common devices. Therefore, two low-cost techniques are proposed and used to increase the capability of the system. In the first method, a parabolic reflector is designed, fabricated and placed behind the system to reflect the beam of parallel rays and concentrates the radiation power at the harvester surface. An alternate technique to boost the output DC power is based on using multi-square-loop collectors. Instead of using a rectifier circuit for each loop collector, multi collectors are combined before feeding into a single rectifier circuit. The experimental results show that these two techniques have significant improvement in the DC output power. The parabolic reflector technique can improve the DC output power by 35%, while in the case of the multi collectors technique, 4 times higher DC output power can be achieved

Ultra-Wideband (UWB) rectenna design for Electromagnetic Energy Harvesting

Projecte fet en col.laboració amb Pontificia Universidad Católica del Perú i Centre Tecnològic de Telecomunicacions de CatalunyaThis work focuses on designing, fabricating, measuring and testing each component of a Rectenna. A rectenna consists of an antenna and a rectifier circuit that is optimized for incoming signals of low power density. This rectenna is used to harvest electric energy from the RF signals that have been radiated at:  GSM-850  GSM-900 (downlink: 935-960MHz)  GSM-1800 (downlink: 1805-1880MHz)  ISM band centered in 2.45 GHz. This work contains antenna design techniques using Ansoft HFSS software and methods to simulate rectennas using Harmonic Balance and electromagnetic full-wave Momentum with the Agilent Advanced Design Software (ADS2008). For the antenna fabrication it was used a LPKF Milling machine. And for measurements a Vector Network Analyzer (VNA), spectral analyzer, analog signal generator, multimeter, and anechoic chamber were used

Current Developments of RF Energy Harvesting System for Wireless Sensor Networks

Energy harvesting or energy scavenging is basically a conversion process of the ambient energy into the electrical energy. The ambient energy exists around us in many different forms including thermal, chemical, electrical and radio frequency (RF). This technique significantly reduces the costs of replacing batteries periodically. Hence, energy harvesting offers various environmental friendly alternative energy sources, which include the vibration, electromagnetic wave, wind energy and solar power. This study will focus on RF energy harvesting that involves the generating of a small amount of the electrical power to drive circuits in wireless communication electronics devices. Recently, wireless sensor network (WSN) has been a crucial part of our daily life. The importance of WSN can be described by the use of sensors in many devices for home security including light sensors, room thermostat and alarm systems. This paper presents an overview and the progress achieved in RF energy harvesting, which involves the integration of antenna with rectifying circuit. Different combinations of antenna and rectifier topologies yield diverse results. Therefore, this study is expected to give an indication on the appropriate techniques to develop an efficient RF energy harvesting system

Microwave Antennas for Energy Harvesting Applications

In the last few years, the demand for power has increased; therefore, the need for alternate energy sources has become essential. Sources of fossil fuels are finite, are costly, and causes environmental hazard. Sustainable, environmentally benign energy can be derived from nuclear fission or captured from ambient sources. Large-scale ambient energy is widely available and large-scale technologies are being developed to efficiently capture it. At the other end of the scale, there are small amounts of wasted energy that could be useful if captured. There are various types of external energy sources such as solar, thermal, wind, and RF energy. Energy has been harvested for different purposes in the last few recent years. Energy harvesting from inexhaustible sources with no adverse environmental effect can provide unlimited energy for harvesting in a way of powering an embedded system from the environment. It could be RF energy harvesting by using antennas that can be held on the car glass or building, or in any places. The abundant RF energy is harvested from surrounding sources. This chapter focuses on RF energy harvesting in which the abundant RF energy from surrounding sources, such as nearby mobile phones, wireless LANs (WLANs), Wi-Fi, FM/AM radio signals, and broadcast television signals or DTV, is captured by a receiving antenna and rectified into a usable DC voltage. A practical approach for RF energy harvesting design and management of the harvested and available energy for wireless sensor networks is to improve the energy efficiency and large accepted antenna gain. The emerging self-powered systems challenge and dictate the direction of research in energy harvesting (EH). There are a lot of applications of energy harvesting such as wireless weather stations, car tire pressure monitors, implantable medical devices, traffic alert signs, and mars rover. A lot of researches are done to create several designs of rectenna (antenna and rectifier) that meet various objectives for use in RF energy harvesting, whatever opaque or transparent. However, most of the designed antennas are opaque and prevent the sunlight to pass through, so it is hard to put it on the car glass or window. Thus, there should be a design for transparent antenna that allows the sunlight to pass through. Among various antennas, microstrip patch antennas are widely used because they are low profile, are lightweight, and have planar structure. Microstrip patch-structured rectennas are evaluated and compared with an emphasis on the various methods adopted to obtain a rectenna with harmonic rejection functionality, frequency, and polarization selectivity. Multiple frequency bands are tapped for energy harvesting, and this aspect of the implementation is one of the main focus points. The bands targeted for harvesting in this chapter will be those that are the most readily available to the general population. These include Wi-Fi hotspots, as well as cellular (900/850 MHz band), personal communications services (1800/1900 MHz band), and sources of 2.4 GHz and WiMAX (2.3/3.5 GHz) network transmitters. On the other hand, at high frequency, advances in nanotechnology have led to the development of semiconductor-based solar cells, nanoscale antennas for power harvesting applications, and integration of antennas into solar cells to design low-cost light-weight systems. The role of nanoantenna system is transforming thermal energy provided by the sun to electricity. Nanoantennas target the mid-infrared wavelengths where conventional photo voltaic cells are inefficient. However, the concept of using optical rectenna for harvesting solar energy was first introduced four decades ago. Recently, it has invited a surge of interest, with different laboratories around the world working on various aspects of the technology. The result is a technology that can be efficient and inexpensive, requiring only low-cost materials. Unlike conventional solar cells that harvest energy in visible light frequency range. Since the UV frequency range is much greater than visible light, we consider the quantum mechanical behavior of a driven particle in nanoscale antennas for power harvesting applications

Düşük güçte çalışan sensörler i̇çi̇n bi̇r radyo frekansı enerji̇ hasatlayıcı devre tasarımı ve geli̇şti̇ri̇lmesi̇

This thesis presents a systematic design and implementation of a rectenna. As a beginning, a receiving antenna is proposed. In the design of the receiving antenna, a fractal topology is utilized to widen the antenna bandwidth. Moreover, a rectifier circuit with a proposed dualband matching technique is realized to aggregate the DC power. Ultimately, the broadband fractal antenna and the proposed dual-band rectifier circuit have been assembled to realize the rectenna. In addition, a simple RF spectrum study and a field measurement are conducted to obtain a better understanding of the available electric field density in the Middle East Technical University–Northern Cyprus Campus. Finally, the energy harvesting capability of the proposed rectenna has been verified in both controlled environment (laboratory) and ambient. As a result of the laboratory measurements, the proposed rectenna yields the highest RF-toDC conversion efficiency of 51.9% when the total power density of the two tone signal is 11.1 µW/cm2 . As a result of the ambient measurements, the proposed rectenna features an openvoltage in the range of 195–417 mV in the ambient when the highest electric field densities are 4.137 V/m and 1.818 V/m from the standards of GSM-900 and 3G (UMTS), respectivelyBu tez, bir dogrultucu antenin sistematik tasarımını ve uygunlamasını sunmaktadır. İlk olarak, alıcı antenin bant genişligini arttırmak için fraktal topoloji ile tasarımına yer verilir. Bunun yanında, önerilen çift bantlı empedans uyumlaştırma özelligine sahip bir doğrultucu devresinin tasarımı ele alınır. Son olarak, geniş bantlı alıcı anten ile önerilen dogrultucu devre enerji hasatlayıcı devreyi gerçekleştirmek için birleştirilir. Bunlara ek olarak, Orta Dogu Teknik Üniversitesi Kuzey Kıbrıs Kampüsü’ndeki mevcut elektriksel alan yogunluğunun belirlen mesi için yapılan ölçümler ve sonuçları sunulur. Önerilen dogrultucu anten hem laboratu varda hem de dış ortamda bulunan RF sinyalleri ile test edilir. Laboratuvar ölçümlerinin sonucunda, dogrultucu antenin, iki ton RF sinyalinden gelen ve toplam güç yoğunluğunun 11.1 µW/cm2 oldugu bir test düzeneğinde, sağlayabildiği en yüksek dönüşüm verimliliği % 51.9 olarak kaydedilmiştir. Dış ortamdaki ölçümler sonucunda, dogrultucu antenin elektriksel alan yogunluklarının 4.137 V /m ile 1.818 V/m arasında degiştiği bir dış ortamda, 195 mV ile 417 mV arasında degişen yüksüz çıkış voltajı sağladığı kaydedilmiştir.M.S. - Master of Scienc

Metasurfaces for Antennas, Energy Harvesting and Imaging

Metamaterials are materials with artificial structures, engineered to produce electromagnetic properties not readily available in nature. Metamaterials have generated broad interest and utilization in various applications because of their engineer-able permittivity and permeability. Metasurfaces form the most-used class of metamaterials in all electromagnetic applications, from microwave to optical, because of their simplicity compared to bulky 3D structures. Metasurfaces are created using an ensemble of electrically small resonators. Previously, the metasurface concept was used to redirect or focus light, with the surface profile being tailored to control the phase and magnitude of the current at each cell. In the first part of this dissertation, a metasurface is used to create a new antenna concept by tailoring the feed for each resonator to create optimal radiation behaviour. The resonators are placed on a flat surface and connected to one feed point using different feed mechanisms to achieve desired current phase at each resonator. Unlike conventional array antennas, in which the distance between adjacent antennas is maintained at approximately half the wavelength to reduce mutual coupling between adjacent antennas, here the distance between the radiating elements is electrically very small. This effects good impedance matching of each resonator to its feed. The metasurface antenna has strong potential for a variety of traditional and non-traditional applications. Its flexible design (high degree of optimization freedom) facilitates its use on a variety of non-Cartesian and platforms. A prototype was fabricated and tested, showing positive agreement between numerical simulations and experimental results of the metasurface antenna. In this part, a concept is presented to enable a systematic design of low-profile conformal antennas. The concept is based on using closely spaced electrically-small radiators. An ensemble of the radiators is placed in a periodic arrangement and the phase of the feed for each element is set to create a phase front orthogonal to the direction where maximum radiation is desired. The phase front is created based on the assumption that each electrically-small radiator is essentially a Huygens source radiating in the open space. A novel method is proposed in the second part of the thesis that emerge metasurface for energy harvesting and wireless power transfer. Unlike earlier designs of metamaterial harvesters where each small resonator was connected to a load, in this design, the power received by the resonators is channeled collectively into one load, thus maximizing the power density per load. Another contribution of the metasurface harvester of this work, based on the concept of perfect absorbance and channeling to one load, is the design of a metasurface medium with near unity electromagnetic energy harvesting. Two different feed networks with different impedances matching techniques are proposed to deliver the maximum power collected by all cells to just one load. Prototypes were fabricated and tested; the numerical simulation and the experimental measurements showed that the proposed metasurface harvester was sufficient to collect microwave energy and deliver it to one load through vias using one feed network. The third part presents a new paradigm of imaging objects using metasurfaces. In this part, an extensive study has been done to examine the metasurface panels for imaging. In conventional imaging methods, a raster scan is used to sense any differences or changes in the object, whereas here, objects are imaged without any scan. The mothed leveraging the voltage from each cell and by using a simple Matlab code these voltages will build the image of the object. This method showed promising results through the numerical simulation of imaging for both metal and dielectric materials

Optically transparent UWB antenna for wireless application & energy harvesting

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.Transparent UWB antennas have been the focus of this PhD research. The use of transparent UWB antennas for stealth and energy harvesting has been the underlying applications that have given impetus to this research. Such transparent antennas being built on materials that are discreet, flexible, conformal, conductive and having the ability to provide good antenna performance on glass to serve as the ‘last mile’ link in subsequent generation communications after 4G have been the basis for this contention. UWB in this regard is able to provide the transmission and reception of high data rates and fast video transmission that is an elementary demand of even a 4G wireless communications system. The integration of UWB antennas with photovoltaic to provide integral energy harvesting solutions that will further enhance the value of the UWB system in terms of cost effectiveness and performance are thus the basis of this work. This work hence starts with the study of a transparent conductive oxide polymer, AgHT and its properties, and culminates in the development of a transparent UWB antenna, which can be integrated with photovoltaic for window glass applications on homes and buildings. Other applications such transparent antennas can find use for like on-body wireless communications in healthcare monitoring was also analysed and presented. The radar absorbing material (RAM) property of the AgHT was investigated and highlighted using CST simulation software, as no measurement facilities were available. The transparent UWB antenna in lieu of the inherent absorbent property of the AgHT material is thus able to exhibit stealth characteristics, a feature that would be much desired in military communications. Introduction of a novel method of connecting the co-axial connector to the feed of the antenna to improve gain and efficiency of transparent polymer based antennas and the development of a UWB antenna that maintains its Omni-directional characteristic instead of becoming directional on an amorphous silicon solar cell are presented as some of the contributions for this research work. Some preliminary analysis on the impact of glass on UWB antennas for video transmission and how to improve transmission is presented. The ability of the conductive part of the antenna radiator to be used as a RF and microwave harvester and how it can further add value to a transparent UWB antenna is presented by way of experimental data. Finally yet importantly, this thesis presents some insight into how transparent antennas may be used in Green Technology Buildings to provide an integrated solution for both wireless communications and energy harvesting as part of the future work. Improvement to the aesthetics of the external appearance of residential buildings through the integration of transparent satellite dish onto solar panels on rooftops is also discussed and illustrated as part of this future work

An experimental strategy for characterizing inductive electromagnetic energy harvesters

Condition monitoring of high voltage power lines through self-powered sensor systems has become a priority for utilities with the aim of detecting potential problems, enhancing reliabilityof the power transmission and distribution networks and mitigating the adverse impact of faults. Energy harvesting from the magnetic field generated by the alternating current flowing through highvoltage lines can supply the monitoring systems with the required power to operate without relying onhard-wiring or battery-based approaches. However, developing an energy harvester, which scavengesthe power from such a limited source of energy, requires detailed design considerations, which maynot result in a technically and economically optimal solution. This paper presents an innovativesimulation-based strategy to characterize an inductive electromagnetic energy harvester and the power conditioning system. Performance requirements in terms of the harvested power and output voltage range, or level of magnetic core saturation can be imposed. Different harvester configurations, whichsatisfy the requirements, have been produced by the simulation models. The accuracy and efficiency ofthis approach is verified with an experimental setup based on an energy harvester, which consists ofa Si-steel magnetic core and a power conditioning unit. For the worst-case scenario with a primary current of 5 A, the maximum power extracted by the harvester can be as close as 165 mW, resulting ina power density of 2.79 mW/cm3.Comunidad de MadridAgencia Estatal de Investigació