Integration of an RFID reader antenna with a work glove

RFIDs are widely deployed in the daily life and its application has been growing with the development of the technologies. RFID application includes everything from the card payment systems to military purposes. In the recent decades, there is significant work done on the tags and various tags have been developed depending on the application requirements, but not much work has been done on the wearable RFID readers. A significant step toward making the RFID reader wearable is to develop wearable RFID reader antenna with considerable read range In this thesis, two types of antennas—slotted patch antenna and split ring resonator antenna—are fabricated and their performance on the human hand is analyzed. The material selected as a substrate is EPDM foam material with permittivity 1.26 and tangent loss 0.007. The thickness of the substrate differs in the fabrication of both the antennas. In case of the slotted patch antenna, the substrate thickness is 4mm, whereas, in case of split ring resonator antenna, the thickness of the substrate is 3mm. The material of the radiating element needed to be flexible and with good conductivity. For this reason, nickel plated conductive textile with sheet resistance 0.16Ω/square is used for fabrication. The summary of the results shows the designed antenna is capable of operating on the desired frequency range. However, the SRR antenna is more flexible, lightweight and bendable with the same read range. For the free space measurement, both the antennas showed good agreement between the measured and simulated results. However, due to inaccuracies in the fabrication of the antennas, the resonance frequency is shifted to other frequencies. In addition to that, bending in two planes i.e xz and yz planes, are performed and results are measured. It is observed that the bending effects the return loss and bandwidth of the antenna, when the antenna is bending is along the effective length of the antenna. The reason for the resonance frequency shifting is that it changes the slot dimension of the antenna, which ultimately affects the current path on the antenna surface. Both antennas showed nearly equal read ranges when the Voyantic Reference tag is measured with both the antennas

Novel Passive RFID Temperature Sensors Using Liquid Crystal Elastomers

When transporting perishable foods in the Cold Supply Chain (CSC), it is essential that they are maintained in a controlled temperature environment (typically from -1° to 10°C) to minimize spoilage. Fresh-food products, such as, meats, fruits, and vegetables, experience discoloration and loss of nutrients when exposed to high-temperatures. Also, medicines, such as, insulin and vaccines, can lose potency if they are not maintained at the appropriate temperatures. Consequently, the CSC is critical to the growth of global trade and to the worldwide availability of food and health supplies; especially, when considering that the retail food market consists mostly (approximately 65%) of fresh-food products. The current method of temperature monitoring in the CSC is limited to discrete location-based measurements. Subsequently, this data is used to assess the overall quality of transported goods. As a result, this method cannot capture all the common irregularities that can occur during the delivery cycle. Therefore, an effective sensor solution to monitor such items is necessary. Radio Frequency Identification (RFID) is a pragmatic wireless technology with a standardized communication protocol. Thus far, passive RFID temperature sensors have been investigated. However, each design has a limitation from which a set of design guidelines for an improved sensor solution is developed. That is, the new sensor should: (a) be compact to be applicable on individual products, (b) utilize purely passive technology to ensure longevity and cost-effectiveness, (c) monitor goods in a continuous fashion (e.g., operate through multiple room-to-cold and cold-to-room temperature cycles), and (d) operate in an independent mode, so that no resetting is required. In this research, antenna systems and RF circuit design techniques are combined with Liquid Crystal Elastomers (LCEs) to develop three novel temperature sensors. LCEs are temperature responsive polymers that are programmable and reversible. Notably, LCEs return to their original state when the stimulus is removed. Also, for the first time, cold-responsive LCEs are incorporated into the designs presented in this research. Two of the developed sensors convey temperature changes through the controlled shift in the operating frequency. The third design conveys temperature threshold crossings by reversibly switching operation between two RFID ICs (or two Electronic Product Codes). Finally, all designs have been fabricated and tested with favorable results in accordance to the above mentioned guidelines

Desenho de antenas para sensores passivos em materiais não convencionais

Doutoramento em Engenharia EletrotécnicaMotivado pela larga expansão dos sistemas RFID e com o desenvolvimento do conceito de Internet das Coisas, a evolução no desenho e métodos de produção de antenas em suportes de materiais alternativos tem tido uma exploração intensiva nos últimos anos. Isto permitiu, não só o desenvolvimento de produtos no campo da interação homem-máquina, mas também tornar estes produtos mais pequenos e leves. A procura de novas técnicas e métodos para produzir eletrónica impressa e antenas em materiais alternativos e, portanto, uma porta aberta para o aparecimento de novas tecnologias. Isto aplica-se especialmente no mercado dos sensores, onde o peso, o tamanho, o consumo energético, e a adaptabilidade a diversos ambientes, têm grande relevância. Esta tese foca-se no desenvolvimento de antenas com suporte em materiais não convenvionais, como os já testados papel e têxteis, mas também na exploração de outros, desconhecidos do ponto de vista eléctrico, como a cortiça e polímeros biodegradáveis usados em impressão 3D. Estes materiais são portanto usados como substrato, ou material de suporte, para diversas antenas e, como tal, as propriedades electromagnéticas destes materiais têm de ser determinadas. Assim, e apresentado neste documento uma revisão de métodos de caracterização de materiais, bem como a proposta de um método baseado em linhas de trasmissão impressas, e a respectiva caracterização electromagnética de diversos materiais. Além disso, são propostos desenhos de antenas para diversos cenários e aplicações utilizando os materiais anteriormente mencionados. Com esta tese concluiu-se que a utilização de materiais alternativos e hoje uma realidade e os resultados obtidos são muito encorajodares para o desenvolvimento de um conjunto de sensores para aplicações RFID com uma grande capacidade de integração.The advancement of the design and fabrication of antennas using textiles or paper as substrates has rapidly grown motivated by the boom of RFID systems and the developing concept of the Internet of Things. These advancements have allowed, not only the development of products for manmachine interaction, but also to make these products smaller and lighter. The search for new techniques and methods to produce printed electronics and antennas in alternative materials is therefore an open door for new technologies to emerge. Especially in the sensors market, where weight, size, power consumption and the adaptability to the target application, are of great importance. This thesis focuses on the development of antenna design approaches with alternative materials, such as the already tested paper and textiles, but also others relatively unknown, such as cork and biodegradable polymers used in 3D printing. These materials are applied to act as substrates, or support structures for the antennas. Therefore, their electromagnetic properties need to be determined. Due to that, a review of electromagnetic characterization methods, as well as the proposal of a custom method based on printed transmission lines, is presented in this document. Besides, several antenna designs, for di erent application scenarios, using the previously mentioned materials, are proposed. With this thesis it was proved that it is possible to develop passive sensors in di erent alternative materials for RFID applications and others, which shows great promise in the use of these materials to achieve higher integration in sensing and identi cation applications

High Impedance Surface – Electromagnetic Band Gap (HIS-EBG) Structures for Magnetic Resonance Imaging (MRI) Applications

High Impedance Surface – Electromagnetic Band Gap (HIS-EBG) structures are one class of Metamaterials with unique and useful electromagnetic properties. This thesis proposes the first application of EBG structures for Magnetic Resonance Imaging (MRI) applications, with the aim of improving effectiveness of coils in creating RF magnetic flux density inside the patient or a phantom. The anti-phase currents in the metallic ground planes placed underneath transmit RF coils for ultrahigh field MRI represent the main reason for the reduction in RF magnetic flux density above these coils (inside the load). In addition, they support the propagation of surface waves which radiate from edges and corners wasting power in the back hemisphere. The objective of this thesis is to investigate the potential of improving the efficiency of a well-established RF coil for 7 Tesla MRI by replacing the standard ground planes with specially designed EBG structures which exhibit novel electromagnetic properties: The reflection of such structures exhibits a frequency range over which an incident electromagnetic wave does not experience a phase reversal, and the image currents appear in-phase rather than out of phase as they do on the standard ground planes. Due to this, the EBG structure is termed an artificial magnetic conductor. Furthermore, it suppresses the propagation of surface waves. In this thesis, novel EBG structures are proposed and fabricated, and their electromagnetic properties are characterized analytically, numerically, and are validated by measurements. The RF coil backed by our proposed EBG ground planes exhibits improvement in the magnetic flux density inside phantoms compared to the case when it is backed by conventional ground planes of the same dimensions. A novel multilayer offset stacked polarization dependent EBG structure is designed to work as a soft surface with anisotropic surface impedance. The designed structure solves the problem of the limited space available in MRI magnet bores. The RF coil backed by the proposed soft surface exhibits stronger magnetic field inside the phantom, while the electric field and the specific energy absorption rate values are reduced.High Impedance Surface – Electronic Band Gap (HIS-EBG) Strukturen für den Einsatz in der Magnetoresonanz-Tomographie (MRT) High Impedance Surface – Electronic Band Gap (HIS-EBG) Strukturen bilden eine Klasse von Metamaterialien mit einzigartigen elektromagnetischen Eigenschaften, welche nicht ohne weiteres in der Natur vorkommen. In dieser Arbeit werden zum ersten Mal EBG Strukturen für den Einsatz in Ultra-Hochfeld Magnetresonanz-Tomographie Anwendungen vorgeschlagen, mit dem Ziel die Effektivität von Spulen, welche für die Erzeugung von hochfrequenten magnetischen Flussdichten in Patienten oder Phantomen verwendet werden, zu erhöhen. Gegenphasige Ströme in den metallischen Masseflächen unterhalb der HF Sende-Spulen sind der Hauptgrund für die Reduzierung der hochfrequenten magnetischen Flussdichten oberhalb dieser Spulen. Ferner kommt es zur Anregung von Oberflächenwellen auf den metallischen Masseflächen und zur Abstrahlung an den Kanten und Ecken, wodurch Leistung in eine unerwünschte Richtung abgestrahlt wird. Das Ziel dieser Arbeit ist die Untersuchung der Möglichkeiten zur Verbesserung des Wirkungsgrads von gängigen HF Spulen für 7 Tesla MRT, bei welchen die Standard- Massefläche durch speziell entworfene EBG Strukturen ersetzt wurde. Bei der Reflektion an solchen Strukturen erfährt die einfallende elektromagnetische Welle in einem bestimmten Frequenzbereich keine Umkehrung der Phase. Im Gegensatz zur Standard-Massefläche, in welcher gegenphasige Ströme entstehen, sind die Ströme in der EBG Struktur gleichphasig. Auf Grund dessen werden die EBG Strukturen als künstliche magnetische Leiter bezeichnet. Des Weiteren wird die Ausbreitung von Oberflächenwellen in EBG Strukturen unterdrückt. In dieser Arbeit, werden einige neuartige EBG Strukturen vorgestellt. Die elektromagnetischen Eigenschaften dieser Strukturen werden sowohl analytisch als auch nummerisch beschrieben und messtechnisch validiert. Die HF Spulen über der EBG Struktur weisen, im Vergleich zum Aufbau über einer herkömmlichen Massefläche, eine deutlich erhöhte magnetische Flussdichte im inneren des Phantoms auf. Des Weiteren wurde eine neuartige, versetzt aufgebaute und polarisationsabhängige Multilagen-EBG Struktur entworfen mit reduzierten Abmessungen um als anisotrope „Soft“-Oberflächenimpedanz fungieren zu können. Die HF Spule über dieser vorgeschlagenen „Soft“ Oberflächenimpedanz führt im inneren des Phantoms zu einer Erhöhung der magnetischen Feldstärke, wobei die Elektrische Feldstärke und die Spezifische Absorptionsrate reduziert werden

Design of an Ultra-wideband Radio Frequency Identification System with Chipless Transponders

The state-of-the-art commercially available radio-frequency identification (RFID) transponders are usually composed of an antenna and an application specific integrated circuit chip, which still makes them very costly compared to the well-established barcode technology. Therefore, a novel low-cost RFID system solution based on passive chipless RFID transponders manufactured using conductive strips on flexible substrates is proposed in this work. The chipless RFID transponders follow a specific structure design, which aim is to modify the shape of the impinged electromagnetic wave to embed anidentification code in it and then backscatter the encoded signal to the reader. This dissertation comprises a multidisciplinary research encompassing the design of low-cost chipless RFID transponders with a novel frequency coding technique, unlike usually disregarded in literature, this approach considers the communication channel effects and assigns a unique frequency response to each transponder. Hence, the identification codes are different enough, to reduce the detection error and improve their automatic recognition by the reader while working under normal conditions. The chipless RFID transponders are manufactured using different materials and state-of-the-art mass production fabrication processes, like printed electronics. Moreover, two different reader front-ends working in the ultra-wideband (UWB) frequency range are used to interrogate the chipless RFID transponders. The first one is built using high-performance off-theshelf components following the stepped frequency modulation (SFM) radar principle, and the second one is a commercially available impulse radio (IR) radar. Finally, the two readers are programmed with algorithms based on the conventional minimum distance and maximum likelihood detection techniques, considering the whole transponder radio frequency (RF) response, instead of following the commonly used approach of focusing on specific parts of the spectrum to detect dips or peaks. The programmed readers automatically identify when a chipless RFID transponder is placed within their interrogation zones and proceed to the successful recognition of its embedded identification code. Accomplishing in this way, two novel fully automatic SFM- and IRRFID readers for chipless transponders. The SFM-RFID system is capable to successfully decode up to eight different chipless RFID transponders placed sequentially at a maximum reading range of 36 cm. The IR-RFID system up to four sequentially and two simultaneously placed different chipless RFID transponders within a 50 cm range.:Acknowledgments Abstract Kurzfassung Table of Contents Index of Figures Index of Tables Index of Abbreviations Index of Symbols 1 Introduction 1.1 Motivation 1.2 Scope of Application 1.3 Objectives and Structure Fundamentals of the RFID Technology 2.1 Automatic Identification Systems Background 2.1.1 Barcode Technology 2.1.2 Optical Character Recognition 2.1.3 Biometric Procedures 2.1.4 Smart Cards 2.1.5 RFID Systems 2.2 RFID System Principle 2.2.1 RFID Features 2.3 RFID with Chipless Transponders 2.3.1 Time Domain Encoding 2.3.2 Frequency Domain Encoding 2.4 Summary Manufacturing Technologies 3.1 Organic and Printed Electronics 3.1.1 Substrates 3.1.2 Organic Inks 3.1.3 Screen Printing 3.1.4 Flexography 3.2 The Printing Process 3.3 A Fabrication Alternative with Aluminum or Copper Strips 3.4 Fabrication Technologies for Chipless RFID Transponders 3.5 Summary UWB Chipless RFID Transponder Design 4.1 Scattering Theory 4.1.1 Radar Cross-Section Definition 4.1.2 Radar Absorbing Material’s Principle 4.1.3 Dielectric Multilayers Wave Matrix Analysis 4.1.4 Frequency Selective Surfaces 4.2 Double-Dipoles UWB Chipless RFID Transponder 4.2.1 An Infinite Double-Dipole Array 4.2.2 Double-Dipoles UWB Chipless Transponder Design 4.2.3 Prototype Fabrication 4.3 UWB Chipless RFID Transponder with Concentric Circles 4.3.1 Concentric Circles UWB Chipless Transponder 4.3.2 Concentric Rings UWB Chipless RFID Transponder 4.4 Concentric Octagons UWB Chipless Transponders 4.4.1 Concentric Octagons UWB Chipless Transponder Design 1 4.4.2 Concentric Octagons UWB Chipless Transponder Design 2 4.5 Summary 5. RFID Readers for Chipless Transponders 5.1 Background 5.1.1 The Radar Range Equation 5.1.2 Range Resolution 5.1.3 Frequency Band Selection 5.2 Frequency Domain Reader Test System 5.2.1 Stepped Frequency Waveforms 5.2.2 Reader Architecture 5.2.3 Test System Results 5.3 Time Domain Reader 5.3.1 Novelda Radar 5.3.2 Test System Results 5.4 Summary Detection of UWB Chipless RFID Transponders 6.1 Background 6.2 The Communication Channel 6.2.1 AWGN Channel Modeling and Detection 6.2.2 Free-Space Path Loss Modeling and Normalization 6.3 Detection and Decoding of Chipless RFID Transponders 6.3.1 Minimum Distance Detector 6.3.2 Maximum Likelihood Detector 6.3.3 Correlator Detector 6.3.4 Test Results 6.4 Simultaneous Detection of Multiple UWB Chipless Transponders 6.5 Summary System Implementation 7.1 SFM-UWB RFID System with CR-Chipless Transponders 7.2 IR-UWB RFID System with COD1-Chipless Transponders 7.3 Summary Conclusion and Outlook References Publications Appendix A RCS Calculation Measurement Setups Appendix B Resistance and Skin Depth Calculation Appendix C List of Videos Test Videos Consortium Videos Curriculum Vita

Pop-Up Stretchable Sensor Designs Using Multiphysics Modeliing

Stretchable electronic devices are critical for the future of wearable sensor technology, where existing rigid and non-flexible devices severely limit the applicability of them in many areas. Stretchable electronics extend flexible electronics one step further by introducing significant elastic deformation. Stretchable electronics can conform to curvy geometries like human skin which enables new applications such as fully wearable electronics whose properties can be tuned through mechanical deformation. Much of the effort in stretchable electronics has focused on investigation of the optimum fabrication method to make a trade-off between the manufacturing cost and acceptable performance. Here in this thesis a novel pop-up strain sensor design is introduced and tested.This technique is simple to use and can be applied to almost all available materials such as metals, dielectrics, semiconductors and different scales from centi-meter to nanoscale. Using this method three main electronic devices have been designed for different applications. The first category is pop-up antennas that are able to reconfigure their frequency response with respect to the mechanical deformation by out of plane displacement. The second category is pop-up frequency selective surface which similarly can change its frequency behaviour due to applied strain. This ability to accommodate the applied stress by three-dimensional (3D) deformation, making these devices ideal for strain sensing applications such as vapor sensing or on skin mountable sensors. Using the advantage of RFID technology in terms of wireless monitoring, the third category has been introduced which is a pop-up capacitor sensor integrating with an RFID chip to detect finger joint bending that can help those patients who are recovering after stroke. The proposed devices have been modelled using COMSOL Multiphysics and Extensive evaluations of the prototype system were conducted on purpose-built laboratory scale test rigs. Both results are in good correlation which makes them applicable for sensing purposes

Characterization of embroidered dipole-type RFID tag antennas

Radio Frequency Identification (RFID) is a technology which is used for automatic identification of objects. A typical RFID system consists of a stationary radio-scanner unit, called reader, and a movable transponder, called tag, which is attached to an object. The tags include an antenna and a microchip with internal read/write memory. Tag antenna plays an important role in the overall RFID system performance factors, such as the read range, and the compatibility with tagged objects. This thesis focuses on garment-integrated embroidered tags which can be used for the means of human monitoring and identification. The embroidered tag antennas are sewed on fabric using conductive threads and computer aided sewing machine. Modeling of embroidered tag antennas is not a straightforward task, because embroidered antennas do not have a distinct conductivity, which could be used in the simulation model of them. In fact, conductivity of sewed flat conductive layer depends on the selection of the conductive thread, the thread and stitch density and the sewing pattern. The aim of this thesis has been to investigate the effect of these factors on the conductivity, and evaluate conductivity values for the embroidered dipole-type RFID tag antennas. In this project, T-matched dipoles have been sewed on cotton with two different sewing patterns and also with many different stitch densities. The effect of the geometry of the antenna is also investigated by sewing and measuring straight simple dipoles with both sewing patterns. The achieved read range values of the sewed tag antennas have been up to 7.5 m. In this thesis it is proved that each sewing pattern has its own conductivity and con-ductivity of a sewing pattern improves if the pattern consists of sewed lines along the direction of current flow. It is not necessary to sew the antenna with a high thread and stitch density. We can achieve high conductivities even from very sparsely sewed an-tennas, using less conductive threads and spending considerably less time on sewing. The evaluated conductivities and the presented simulation model of the sewed dipoles in this project can be used in future for optimization of the sewed antennas to operate in the vicinity of body

Metamaterial-loaded printed antennas : design and application

Wireless communication systems have grown dramatically during the last few years. Moreover, these systems have achieved a great popularity in society. Several examples can be mentioned: cellular communications (GSM, DCS, UMTS), personal area networks (Bluetooth), local area wireless networks (WiFi), radionavigation systems (GPS), etc. The current trend consists of using only one user terminal for several standards (e. g. GSM and UMTS terminals) and for more than one service (e. g. cellular communications, radionavigation systems and personal area networks). In addition, it is also important to note that current user terminals are more and more compact. For these reasons, it would be desirable to use only one antenna for all the standards and/or services covered by the terminal. However, it is important to note that each standard or service requires different antenna characteristics in terms of operating frequency and optimal radiation performance (radiation pattern, polarization, etc.). Hence, compact antennas with multifrequency (simultaneous operation over two or more bands) and multifunction performance (radiation pattern or polarization diversity, frequency reconfigurability, etc.) are a good solution as the radiating element of hanheld terminals. Furthermore, similar arguments can be made to justify the huge demand on multifrequency and multifunction compact antennas for the network elements such as base stations, hot-spots and other access points. Additionally, novel proposals, such as Cognitive Radio, and emerging radio applications like RFID are challenging from antenna engineering point of view. It is important to take into account that the antennas with the optimal characteristics stated above are very difficult to achieve by using conventional techniques. Thus, novel approaches are being developed to obtain radiating elements with the desired characteristics. One of these techniques is the use of metamaterial structures. Metamaterials can be broadly defined as electromagnetic structures engineered to achieve exotic or unusual properties. These features have been used in microwave engineering to develop devices with extraordinary properties such as miniaturization or operation over multiple frequency bands. On the other hand, the effort in the antenna field has been put on the use of metamaterials for travelling-wave antennas and as substrates and superstrates for antennas. Recently, there has been a great effort on miniaturized antennas based on metamaterial concepts. Nevertheless, from the author's point of view, the possibility of achieving multifrequency and/or multifunction antennas based on metamaterials has not been fully explored. The main goal of the proposed Thesis is the development of a novel design approach called metamaterial-loaded printed antennas. This solution consists of loading a conventional printed antenna with a set of metamaterial particles. Hence, the bene ts of printed antennas (low cost, compactness, low pro le, light weight, simplicity to integrate with circuitry and usefulness as elements for antenna arrays) are kept. Furthermore, the desired additional characteristics such as multifrequency and multifunction performance are obtained thanks to the proper design of the metamaterial loading elements. Several metamaterial-loaded printed antennas are proposed to provide solutions for a broad range of applications. In particular, two types of printed antennas are considered: printed wire antennas and microstrip patch radiators. The methodology used throughout the Thesis is the following: firstly, approximate models based on transmission line theory and equivalent circuits are developed to analyse and design the proposed antennas with low computational cost. Then, a full-wave study is carried out by making use of commercial and home-made solvers. Finally, the designed antennas are manufactured and measured to check their performance. Two different classes of wire antennas are proposed: printed dipole antennas loaded with metamaterial particles and printed wire antennas over ground plane with Left-Handed (LH) metamaterial loading. Regarding the dipole antennas, a multifrequency performance is achieved because these antennas have additional working bands close to the self-resonance frequencies of the metamaterial loading particles. Moreover, miniaturization is achieved when the additional modes are placed below the resonance frequency of the unloaded dipole. On the other hand, the use of LH loading allows developing antennas over ground plane (the monopole and half-loop antenna over ground plane) with additional features and small dimensions. The second type of antennas is microstrip patch antennas filled with metamaterial structures. Multifrequency and multifunction microstrip patch antennas are developed using this approach. In addition, this technique is extended to achieve multifunction patch antennas with polarization diversity and multifrequency performance. In particular, two applications are proposed: quad-frequency patch antennas with polarization diversity and dualfrequency circularly polarized patch antennas. Finally, it is proposed the application of the metamaterial-loaded antennas not as isolated radiating elements, but integrated into systems or antenna arrays. Specifically, the proposed dipole antennas are used to enhance the performance of log-periodic antenna arrays. Moreover, it is shown that metamaterial-loaded antennas are a good solution to fulfil the requirements of future communications systems (Cognitive Radio) and emerging applications such us RFID.---------------------------------------------------------------------------------------------------Los sistemas de comunicaciones inalámbricos han experimentado un enorme crecimiento en los últimos años. Prueba de ello es que varios de estos sistemas han logrado una gran popularidad. Podemos mencionar los ejemplos de la telefonía móvil (GSM, DCS, UMTS), las redes de área personal (Bluetooth), las redes locales inalámbricas (WiFi), los servicios de radionavegación (GPS), etc. La tendencia actual consiste en emplear un único terminal de usuario para diferentes normas (por ejemplo los terminales que funcionan en GSM y UMTS simultáneamente) y para varios servicios distintos (como los terminales que proporcionan los servicios de telefonía móvil, radionavegación y redes personales). Además, es importante tener en cuenta que los terminales cada vez son más compactos. Por estas razones, sería deseable emplear una única antena para todas las normas y/o servicios en los que funcione el terminal. Sin embargo, hay que tener en cuenta que cada norma o servicio requiere unas características diferentes de la antena tanto desde el punto de vista de la frecuencia de funcionamiento como de las características de radiación (diagrama de radiación, polarización, etc.) De este modo, las antenas compactas con propiedades de multifrecuencia (funcionamiento simultáneo en dos o más bandas de frecuencia) y multifunción (diversidad de diagramas de radiación, reconfigurabilidad en frecuencia, etc.) resultarían una buena solución como elementos radiantes de los terminales de usuario. Además, se pueden considerar argumentos similares para justificar la enorme demanda de antenas multifrecuencia y multifución para los elementos de red como estaciones base, hot-spots y otros puntos de acceso a redes inalámbricas. No podemos obviar tampoco que las nuevas propuestas como los sistemas de radio cognitiva (Cognitive Radio) y otras aplicaciones inalámbricas emergentes como la identificación por radiofrecuencia (RFID) suponen una serie de retos desde el punto de vista de la ingeniería de antenas. Debemos tener en cuenta que es muy difícil diseñar antenas con todas las características mencionadas anteriormente mediante el empleo de las técnicas convencionales. Por esta razón, se están proponiendo nuevas técnicas para el desarrollo de elementos radiantes con las características optimas deseadas. Ona de estas nuevas técnicas está basada en el empleo de las denominadas estructuras metamateriales. Los metamateriales se pueden definir de manera amplia como estructuras electromagnéticas diseñadas para obtener propiedades exóticas o no comunes. Estas características se han empleado en el ámbito de la ingeniería de microondas para el desarrollo de dispositivos con características extraordinarias como son la miniaturización o multifrecuencia. En cambio, en el ámbito de la ingeniería de antenas se han empleado para el diseño de antenas de onda viajera (por ejemplo leaky-wave) y como sustratos o superestratos para antenas. Más recientemente, se ha realizado un gran esfuerzo para obtener antenas miniaturizadas basadas en los conceptos de estructuras metamateriales. Sin embargo, desde el punto de vista del autor, la posibilidad de obtener antenas multifrecuencia y/o multifunción basadas en estructuras metamateriales no ha sido totalmente explotada. El principal objetivo de esta tesis doctoral es el desarrollo de una novedosa técnica de diseño de antenas consistente en cargar una antena impresa convencional con partículas metamateriales. Por este motivo denominamos este conjunto antenas impresas cargadas con partículas metamateriales. Mediante el empleo de esta técnica se mantienen los beneficios de las antenas impresas (bajo coste, antenas compactas y de bajo perfil, bajo peso, simplicidad para integrarlas con circuitería y como elementos en agrupaciones de antenas). Además, se consiguen una serie de características deseadas como multifrecuencia y multifuncionalidad gracias al empleo de las partículas materiales que se emplean para cargar la antena. En concreto, se proponen dos clases de antenas impresas cargadas con partículas metamateriales con el objetivo de cubrir el amplio espectro de aplicaciones que requieren antenas con dichas características. Las dos clases de antenas propuestas son las antenas de hilo impresas cargadas con partículas metamateriales y las antenas de parche parcialmente rellenas de estrucutras metamateriales. La metodología que se sigue durante el desarrollo de esta tesis doctoral es la siguiente: en primer lugar se proponen modelos aproximados de bajo coste computacional basados en la teoría de líneas de transmisión y equivalentes circuitales para el análisis y diseño de las antenas propuestas. A continuación, se realizan simulaciones de onda completa empleando simuladores comerciales y una solución propia del método de los momentos. Finalmente, las antenas diseñadas se fabrican y se miden para comprobar sus prestaciones. Se proponen dos tipos de antenas de hilo impresas: dipolos cargados con partículas metamateriales y antenas de hilo impresas sobre plano de masa cargadas con líneas metamateriales zurdas (conocidas como Left-Handed o LH en la bibliografía técnica). En lo que respecta a los dipolos cargados con partículas metamateriales, se obtiene la característica de multifrecuencia debido a que estas antenas presentan bandas de funcionamiento adicionales próximas a las frecuencias de resonancia de las partículas metamateriales que se emplean para cargarlas. Además, es posible obtener la característica de miniaturización ya que los modos adicionales pueden resonar por debajo de la frecuencia fundamental del dipolo convenconal sin cargar. En cambio, el empleo de estructuras LH en las antenas sobre plano de masa (como son el monopolo y el semilazo sobre plano de masa) proporcionan características adicionales y miniaturización respecto a las antenas convencionales sin cargar. La segunda clase de antenas propuestas son los parches parcialmente rellenos de estructuras metamateriales. El empleo de esta técnica permite el diseño de antenas de parche con las propiedades de multifrecuencia y multifunción. Además, esta técnica se puede emplear también para obtener antenas multifrecuencia con diversidad de polarización. En concreto, se proponen dos aplicaciones distintas: parches de cuádruple frecuencia con diversidad de polarización y parches de doble frecuencia con polarización circular. Finalmente, se propone el empleo de las antenas impresas cargadas con partículas metamateriales no como elementos radiantes aislados, sino integradas en sistemas y agrupaciones de antenas. Por ejemplo, los dipolos impresos multifrecuencia se utilizan para mejorar las características de las agrupaciones log-periódicas. Además, se demuestra que las antenas propuestas son unas buenas candidatas para satisfacer los requisitos de los sistemas de comunicaciones futuros (como Cognitive Radio) y las aplicaciones emergentes como RFID

Biosensors for Diagnosis and Monitoring

Biosensor technologies have received a great amount of interest in recent decades, and this has especially been the case in recent years due to the health alert caused by the COVID-19 pandemic. The sensor platform market has grown in recent decades, and the COVID-19 outbreak has led to an increase in the demand for home diagnostics and point-of-care systems. With the evolution of biosensor technology towards portable platforms with a lower cost on-site analysis and a rapid selective and sensitive response, a larger market has opened up for this technology. The evolution of biosensor systems has the opportunity to change classic analysis towards real-time and in situ detection systems, with platforms such as point-of-care and wearables as well as implantable sensors to decentralize chemical and biological analysis, thus reducing industrial and medical costs. This book is dedicated to all the research related to biosensor technologies. Reviews, perspective articles, and research articles in different biosensing areas such as wearable sensors, point-of-care platforms, and pathogen detection for biomedical applications as well as environmental monitoring will introduce the reader to these relevant topics. This book is aimed at scientists and professionals working in the field of biosensors and also provides essential knowledge for students who want to enter the field