Rectenna Systems for RF Energy Harvesting and Wireless Power Transfer

With the rapid development of the wireless systems and demands of low-power integrated electronic circuits, various research trends have tended to study the feasibility of powering these circuits by harvesting free energy from ambient electromagnetic space or by using dedicated RF source. Wireless power transmission (WPT) technology was first pursued by Tesla over a century ago. However, it faced several challenges for deployment in real applications. Recently, energy harvesting and WPT technologies have received much attention as a clean and renewable power source. Rectenna (rectifying antenna) system can be used for remotely charging batteries in several sensor networks at internet of things (IoT) applications as commonly used in smart buildings, implanted medical devices and automotive applications. Rectenna, which is used to convert from RF energy to usable DC electrical energy, is mainly a combination between a receiving antenna and a rectifier circuit. This chapter will present several designs for single and multiband rectennas with different characteristics for energy harvesting applications. Single and multiband antennas as well as rectifier circuits with matching networks are introduced for complete successful rectenna circuit models. At the end of the chapter, a dual-band rectenna example is introduced with a detailed description for each section of the rectenna

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

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

Microwave antennas for infrastructure health monitoring

Infrastructure health monitoring (IHM) is a technology that has been developed for the detection and evaluation of changes that affect the performance of built infrastructure systems such as bridges and buildings. One of the employed methods for IHM is wireless sensors method which is based on sensors embedded in concrete or mounted on surface of structure during or after the construction to collect and report valuable monitoring data such as temperature, displacement, pressure, strain and moisture content, and information about defects such as cracks, voids, honeycombs, impact damages and delamination. The data and information can then be used to access the health of a structure during and/or after construction. Wireless embedded sensor technique is also a promising solution for decreasing the high installation and maintenance cost of the conventional wire based monitoring systems. However, several issues should be resolved at research and development stage in order to apply them widely in practice. One of these issues is that wireless sensors cannot operate for a long time due to limited lifetime of batteries. Once the sensors are embedded within a structure, they may not be easily accessible physically without damaging the structure. The main aim of this research is to develop effective antennas for IHM applications such as detection of defects such as gaps representing cracks and delaminations, and wireless powering of embeddable sensors or recharging their batteries. For this purpose, modelling of antennas based on conventional antipodal Vivaldi antennas (CAVA) and parametric studies are performed using a computational tool CST Studio (Studio 2015) including CST Microwave Studio and CST Design Studio, and experimental measurements are conducted using a performance network analyser. Firstly, modified antipodal Vivaldi antenna (MAVA) at frequency range of 0.65 GHz – 6 GHz is designed and applied for numerical and experimental investigations of the reflection and transmission properties of concrete-based samples possessing air gap or rebars. The results of gap detection demonstrate ability of the developed MAVA for detection of air gaps and delivery of power to embeddable antennas and sensors placed at any depth inside 350-mm thick concrete samples. The investigation into the influence of rebars show that the rebar cell can act as a shield for microwaves if mesh period parameter is less than the electrical half wavelength. At higher frequencies of the frequency range, microwaves can penetrate through the reinforced concrete samples. These results are used for the investigating the transmission of microwaves at the single frequency of 2.45 GHz between the MAVA and a microstrip patch antenna embedded inside reinforced concrete samples at the location of the rebar cell. It is shown that -15 dB coupling between the antennas can be achieved for the samples with rebar cell parameters used in practice. Secondly, a relatively small and high-gain resonant antipodal Vivaldi antenna (RAVA) as a transmitting antenna and modified microstrip patch antenna as an embeddable receiving antenna are designed to operate at 2.45 GHz for powering the sensors or recharging their batteries embedded in reinforced concrete members. These members included reinforced dry and saturated concrete slabs and columns with different values of mesh period of rebars and steel ratio, respectively. Parametric study on the most critical parameters, which affect electromagnetic (EM) wave propagation in these members, is performed. It is shown that there is a critical value of mesh period of rebars with respect to reflection and transmission properties of the slabs, which is related to a half wavelength in concrete. The maximum coupling between antennas can be achieved at this value. The investigation into reinforced concrete columns demonstrates that polarisation configuration of the two-antenna setup with respect to rebars and steel ratios as well as losses in concrete are important parameters. It is observed that the coupling between the antennas reduces faster by increasing the value of steel ratio in parallel than in vertical configuration due to the increase of the interaction between electromagnetic waves and the rebars. This effect is more pronounced in the saturated than in dry reinforced concrete columns. Finally, a relatively high gain 4-element RAVA array with a Wilkinson power divider, feeding network and an embeddable rectenna consisting of the microstrip patch antenna and a rectified circuit are developed. Two wireless power transmission systems, one with a single RAVA and another with the RAVA array, are designed for recharging batteries of sensors embedded inside reinforced concrete slabs and columns with different configurations and moisture content. Comparison between these systems shows that the DC output voltage for recharging commonly used batteries can be provided by the systems with the single RAVA and the system with the RAVA array at the distance between the transmitting antenna and the surface of reinforced concrete members of 0.12 m and 0.6 m, respectively, i.e. the distance achieved when the array is 5 times longer that the distance achieved with a single antenna

Integrated Filters and Couplers for Next Generation Wireless Tranceivers

The main focus of this thesis is to investigate the critical nonlinear distortion issues affecting RF/Microwave components such as power amplifiers (PA) and develop new and improved solutions that will improve efficiency and linearity of next generation RF/Microwave mobile wireless communication systems. This research involves evaluating the nonlinear distortions in PA for different analog and digital signals which have been a major concern. The second harmonic injection technique is explored and used to effectively suppress nonlinear distortions. This method consists of simultaneously feeding back the second harmonics at the output of the power amplifier (PA) into the input of the PA. Simulated and measured results show improved linearity results. However, for increasing frequency bandwidth, the suppression abilities reduced which is a limitation for 4G LTE and 5G networks that require larger bandwidth (above 5 MHz). This thesis explores creative ways to deal with this major drawback. The injection technique was modified with the aid of a well-designed band-stop filter. The compact narrowband notch filter designed was able to suppress nonlinear distortions very effectively when used before the PA. The notch filter is also integrated in the injection technique for LTE carrier aggregation (CA) with multiple carriers and significant improvement in nonlinear distortion performance was observed. This thesis also considers maximizing efficiency alongside with improved linearity performance. To improve on the efficiency performance of the PA, the balanced PA configuration was investigated. However, another major challenge was that the couplers used in this configuration are very large in size at the desired operating frequency. In this thesis, this problem was solved by designing a compact branch line coupler. The novel coupler was simulated, fabricated and measured with performance comparable to its conventional equivalent and the coupler achieved substantial size reduction over others. The coupler is implemented in the balanced PA configuration giving improved input and output matching abilities. The proposed balanced PA is also implemented in 4G LTE and 5G wireless transmitters. This thesis provides simulation and measured results for all balanced PA cases with substantial efficiency and linearity improvements observed even for higher bandwidths (above 5 MHz). Additionally, the coupler is successfully integrated with rectifiers for improved energy harvesting performance and gave improved RF-dc conversion efficienc

A self-powered single-chip wireless sensor platform

Internet of things” require a large array of low-cost sensor nodes, wireless connectivity, low power operation and system intelligence. On the other hand, wireless biomedical implants demand additional specifications including small form factor, a choice of wireless operating frequencies within the window for minimum tissue loss and bio-compatibility This thesis describes a low power and low-cost internet of things system suitable for implant applications that is implemented in its entirety on a single standard CMOS chip with an area smaller than 0.5 mm2. The chip includes integrated sensors, ultra-low-power transceivers, and additional interface and digital control electronics while it does not require a battery or complex packaging schemes. It is powered through electromagnetic (EM) radiation using its on-chip miniature antenna that also assists with transmit and receive functions. The chip can operate at a short distance (a few centimeters) from an EM source that also serves as its wireless link. Design methodology, system simulation and optimization and early measurement results are presented

Sensores passivos alimentados por transmissão de energia sem fios para aplicações de Internet das coisas

Nowadays, the Wireless Sensor Networks (WSNs) depend on the battery duration of the sensors and there is a renewed interest in creating a passive sensor network scheme in the area of Internet of Things (IoT) and space oriented WSN systems. The challenges for the future of radio communications have a twofold evolution, one being the low power consumption and, another, the adaptability and intelligent use of the available resources. Specially designed radios should be used to reduce power consumption, and adapt to the environment in a smart and e cient way. This thesis will focus on the development of passive sensors based on low power communication (backscatter) with Wireless Power Transfer (WPT) capabilities used in IoT applications. In that sense, several high order modulations for the communication will be explored and proposed in order to increase the data rate. Moreover, the sensors need to be small and cost e ective in order to be embedded in other technologies or devices. Consequently, the RF front-end of the sensors will be designed and implemented in Monolithic Microwave Integrated Circuit (MMIC).Atualmente, as redes de sensores sem fios dependem da duração da bateria e,deste modo, existe um interesse renovado em criar um esquema de rede de sensores passivos na área de internet das coisas e sistemas de redes de sensores sem fios relacionados com o espaço. Os desafios do futuro das comunicações de rádio têm uma dupla evolução, sendo um o baixo consumo de energia e, outro, a adaptação e o uso inteligente dos recursos disponíveis. Rádios diferentes dos convencionais devem ser usados para reduzir o consumo de energia e devem adaptar-se ao ambiente de forma inteligente e eficiente, de modo a que este use a menor quantidade de energia possível para estabelecer a comunicação. Esta tese incide sobre o desenvolvimento de sensores passivos baseados em comunicação de baixo consumo energético (backscatter) com recurso a transmissão de energia sem fios de modo a que possam ser usados em diferentes aplicações inseridas na internet das coisas. Nesse sentido, várias modulações de alta ordem para a comunicação backscatter serão exploradas e propostas com o objectivo de aumentar a taxa de transmissão de dados. Além disso, os sensores precisam de ser reduzidos em tamanho e económicos de modo a serem incorporados em outras tecnologias ou dispositivos. Consequentemente, o front-end de rádio frequência dos sensores será projetado e implementado em circuito integrado de microondas monolítico.Programa Doutoral em Engenharia Eletrotécnic