Analysis of RF-energy transducer for microwave harvesting system suitable for IoT applications

This project examines numerically the improved efficiency of energy transducer elements as RF antennas confined in metal cavities. To do so, parametric studies are performed using the 3D electromagnetic simulator CST transducers proposed using two RF antennas dual 2.4/5GHz antenna and a patch-designed 2.4 GHz. The results are contrasted with experimental measurements, demonstrating that the proposed transducers generate enough power to power a Texas Instruments BQ25570 chip or power IoT systems with μW power consumption.Aquest projecte analitza numèricament la millora en eficiència dels elements del transductor d'energia de RF d'antenes confinades en cavitats metàl·liques. Per fer-ho, es realitzen estudis paramètrics mitjançant el simulador electromagnètic 3D CST dels transductors de RF proposats utilitzant dues antenes duals a 2.4/5GHz i una patch-antenna dissenyada a 2.4GHz. Els resultats obtinguts es contrasten amb mesures experimentals, arribant a demostrar que els transductors proposats generen prou potència per a alimentar un sistema de gestió d'energia basat en el xip comercial BQ25570 de Texas Instruments o alimentar sistemes IoT amb consums en el rang del μW.El presente proyecto analiza numéricamente el aumento en eficiencia de los elementos del transductor de energía de RF de antenas confinadas en cavidades metálicas. Para ello, se realiza un estudio paramétrico mediante el simulador electromagnético 3D CST de los transductores de RF propuestos para dos antenas dipolos comerciales duales a 2.4/5GHz y una patch antena diseñada a 2.4GHz. Los resultados de las simulaciones se contrastan con medidas experimentales, llegando a demostrar que el transductor propuesto genera suficiente energía como para alimentar un sistema de gestión de energía estándar basado en el chip comercial BQ25570 de Texas Instrumentos alimentar sistemas IoT con consumos en el rango de los μW

Ambient RF energy harvesting and efficient DC-load inductive power transfer

This thesis analyses in detail the technology required for wireless power transfer via radio frequency (RF) ambient energy harvesting and an inductive power transfer system (IPT). Radio frequency harvesting circuits have been demonstrated for more than fifty years, but only a few have been able to harvest energy from freely available ambient (i.e. non-dedicated) RF sources. To explore the potential for ambient RF energy harvesting, a city-wide RF spectral survey was undertaken in London. Using the results from this survey, various harvesters were designed to cover four frequency bands from the largest RF contributors within the ultra-high frequency (0.3 to 3 GHz) part of the frequency spectrum. Prototypes were designed, fabricated and tested for each band and proved that approximately half of the London Underground stations were found to be suitable locations for harvesting ambient RF energy using the prototypes. Inductive Power Transfer systems for transmitting tens to hundreds of watts have been reported for almost a decade. Most of the work has concentrated on the optimization of the link efficiency and have not taken into account the efficiency of the driver and rectifier. Class-E amplifiers and rectifiers have been identified as ideal drivers for IPT applications, but their power handling capability at tens of MHz has been a crucial limiting factor, since the load and inductor characteristics are set by the requirements of the resonant inductive system. The frequency limitation of the driver restricts the unloaded Q-factor of the coils and thus the link efficiency. The system presented in this work alleviates the use of heavy and expensive field-shaping techniques by presenting an efficient IPT system capable of transmitting energy with high dc-to-load efficiencies at 6 MHz across a distance of 30 cm.Open Acces

Radio frequency energy harvesting for autonomous systems

A thesis submitted to the University of Bedfordshire in partial fulfilment of the requirements for the degree of Doctor of PhilosophyRadio Frequency Energy Harvesting (RFEH) is a technology which enables wireless power delivery to multiple devices from a single energy source. The main components of this technology are the antenna and the rectifying circuitry that converts the RF signal into DC power. The devices which are using Radio Frequency (RF) power may be integrated into Wireless Sensor Networks (WSN), Radio Frequency Identification (RFID), biomedical implants, Internet of Things (IoT), Unmanned Aerial Vehicles (UAVs), smart meters, telemetry systems and may even be used to charge mobile phones. Aside from autonomous systems such as WSNs and RFID, the multi-billion portable electronics market – from GSM phones to MP3 players – would be an attractive application for RF energy harvesting if the power requirements are met. To investigate the potential for ambient RFEH, several RF site surveys were conducted around London. Using the results from these surveys, various harvesters were designed and tested for different frequency bands from the RF sources with the highest power density within the Medium Wave (MW), ultra- and super-high (UHF and SHF) frequency spectrum. Prototypes were fabricated and tested for each of the bands and proved that a large urban area around Brookmans park radio centre is suitable location for harvesting ambient RF energy. Although the RFEH offers very good efficiency performance, if a single antenna is considered, the maximum power delivered is generally not enough to power all the elements of an autonomous system. In this thesis we present techniques for optimising the power efficiency of the RFEH device under demanding conditions such as ultra-low power densities, arbitrary polarisation and diverse load impedances. Subsequently, an energy harvesting ferrite rod rectenna is designed to power up a wireless sensor and its transmitter, generating dedicated Medium Wave (MW) signals in an indoor environment. Harvested power management, application scenarios and practical results are also presented

ULTRA LOW POWER FSK RECEIVER AND RF ENERGY HARVESTER

This thesis focuses on low power receiver design and energy harvesting techniques as methods for intelligently managing energy usage and energy sources. The goal is to build an inexhaustibly powered communication system that can be widely applied, such as through wireless sensor networks (WSNs). Low power circuit design and smart power management are techniques that are often used to extend the lifetime of such mobile devices. Both methods are utilized here to optimize power usage and sources. RF energy is a promising ambient energy source that is widely available in urban areas and which we investigate in detail. A harvester circuit is modeled and analyzed in detail at low power input. Based on the circuit analysis, a design procedure is given for a narrowband energy harvester. The antenna and harvester co-design methodology improves RF to DC energy conversion efficiency. The strategy of co-design of the antenna and the harvester creates opportunities to optimize the system power conversion efficiency. Previous surveys have found that ambient RF energy is spread broadly over the frequency domain; however, here it is demonstrated that it is theoretically impossible to harvest RF energy over a wide frequency band if the ambient RF energy source(s) are weak, owing to the voltage requirements. It is found that most of the ambient RF energy lies in a series of narrow bands. Two different versions of harvesters have been designed, fabricated, and tested. The simulated and measured results demonstrate a dual-band energy harvester that obtains over 9% efficiency for two different bands (900MHz and 1800MHz) at an input power as low as -19dBm. The DC output voltage of this harvester is over 1V, which can be used to recharge the battery to form an inexhaustibly powered communication system. A new phase locked loop based receiver architecture is developed to avoid the significant conversion losses associated with OOK architectures. This also helps to minimize power consumption. A new low power mixer circuit has also been designed, and a detailed analysis is provided. Based on the mixer, a low power phase locked loop (PLL) based receiver has been designed, fabricated and measured. A power management circuit and a low power transceiver system have also been co-designed to provide a system on chip solution. The low power voltage regulator is designed to handle a variety of battery voltage, environmental temperature, and load conditions. The whole system can work with a battery and an application specific integrated circuit (ASIC) as a sensor node of a WSN network

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

IoT応用向け環境RF信号RFエネルギーハーベスティングシステムの研究

電気通信大学201

Scalable Surfaces for Electromagnetic Energy Harvesting and Wireless Power Transfer

The idea of collecting electromagnetic (EM) energy and converting it into various forms of useful power dates back to the early 20th century. Nikola Tesla's wireless power transfer experiments demonstrated the concept first, which was followed by researchers in Japan and the USA in subsequent decades. In terms of a working prototype, the first rectenna for efficient reception and rectification of microwave power was developed in the early 1960s. Later, the introduction of semiconductor diodes and the invention of Schottky diodes were significant developments towards the realization of practical rectennas. Since then, owing to the numerous applications in different technology domains (i.e. consumer electronics, renewable energy, transportation, internet of things, artificial intelligence, telecommunications, defense & space, biomedical engineering), wireless power transfer and EM energy harvesting have attracted significant interest. Harvesting the ambient EM energy has emerged more recently as a promising application with potential for commercial success and contribution to a sustainable future with renewable energy. Many studies have reported the available ambient power densities measured in several parts of the world demonstrating the potentials and limitations of the concept. Traditional single rectenna structures have found very little use due to their inherent limitations at low power densities. Large rectenna arrays or periodic structures covering larger surface areas have become particularly important in order to efficiently harvest and convert the energy. A rectenna consists of two main functional building blocks: the rectifier and the EM collector. The work in this thesis first focuses on improving these functional blocks individually. Regarding the rectifier function; a balanced full-wave rectifier is proposed where the circuit is differentially fed by two separate antennas. This configuration allows the received power to be rectified and transferred into a load between two antennas, making it convenient to channel the harvested power in rectenna arrays. The proposed concept is demonstrated using an array of T-matched dipole antennas at 2.45 GHz. It is also compared with half-wave rectennas that occupy the same footprint with an identical array layout. Measurement results show that, under the same circumstances, the proposed full-wave rectification performs better than the traditional half-wave rectification and it is indeed suitable for energy harvesting rectenna arrays. Regarding the EM collector; a novel Frequency Selective Surface (FSS) is developed as an absorber surface that accepts 98.5% of the available power and collects 97% of it exclusively on its resistive load (only 1.5% is dissipated as dielectric and metallic losses). To demonstrate its performance, a proof of concept FSS absorber is fabricated and its resistive load is replaced with a matched full-wave rectifier. Measurement results show that the overall Radiation-to-dc conversion efficiency of the complete rectenna system reaches 61%, which is considerably higher than the previously reported FSS based rectennas. Subsequent sections in this thesis expand the energy harvesting surface by adding dual-band and dual-polarization capabilities. Design details and simulation results are provided together with measurement results. Fabricated prototypes are tested and their overall performance is evaluated based on the rectified DC power at the system load as percentage of the available EM power on the physical surface area of the rectenna (i.e. radiation-to-dc conversion efficiency). A key contribution of this thesis is the introduction of the scalability concept for energy harvesting. The periodic absorber surfaces presented in this thesis have built-in channelling features that allow multi-cell configurations to feed a single rectifier. This is demonstrated to be an efficient means to increase the EM collector area per rectifier by effortlessly scaling the surface area while efficiently channelling the collected power. As a result, the number of diodes and diode losses are minimized in the system, leading to higher overall rectenna efficiencies. Real life ambient power densities can be on the order of nW/cm2 and the work in this thesis show that larger EM collectors can significantly mitigate the limitations posed by such low power levels. As an example; when integrated with a multi-cell configuration, an ordinary rectifier made with Schottky diodes was efficiently used at a power density that is less than 1/12th of that would be required if the same rectifier were to be used with a traditional single unit cell approach

Development and Demonstration of a TDOA-Based GNSS Interference Signal Localization System

Background theory, a reference design, and demonstration results are given for a Global Navigation Satellite System (GNSS) interference localization system comprising a distributed radio-frequency sensor network that simultaneously locates multiple interference sources by measuring their signals’ time difference of arrival (TDOA) between pairs of nodes in the network. The end-to-end solution offered here draws from previous work in single-emitter group delay estimation, very long baseline interferometry, subspace-based estimation, radar, and passive geolocation. Synchronization and automatic localization of sensor nodes is achieved through a tightly-coupled receiver architecture that enables phase-coherent and synchronous sampling of the interference signals and so-called reference signals which carry timing and positioning information. Signal and crosscorrelation models are developed and implemented in a simulator. Multiple-emitter subspace-based TDOA estimation techniques are developed as well as emitter identification and localization algorithms. Simulator performance is compared to the CramérRao lower bound for single-emitter TDOA precision. Results are given for a test exercise in which the system accurately locates emitters broadcasting in the amateur radio band in Austin, TX.Aerospace Engineering and Engineering Mechanic

Energy harvesting and wireless transfer in sensor network applications: Concepts and experiences

Advances in micro-electronics and miniaturized mechanical systems are redefining the scope and extent of the energy constraints found in battery-operated wireless sensor networks (WSNs). On one hand, ambient energy harvesting may prolong the systems lifetime or possibly enable perpetual operation. On the other hand, wireless energy transfer allows systems to decouple the energy sources from the sensing locations, enabling deployments previously unfeasible. As a result of applying these technologies to WSNs, the assumption of a finite energy budget is replaced with that of potentially infinite, yet intermittent, energy supply, profoundly impacting the design, implementation, and operation of WSNs. This article discusses these aspects by surveying paradigmatic examples of existing solutions in both fields and by reporting on real-world experiences found in the literature. The discussion is instrumental in providing a foundation for selecting the most appropriate energy harvesting or wireless transfer technology based on the application at hand. We conclude by outlining research directions originating from the fundamental change of perspective that energy harvesting and wireless transfer bring about