Near-field chipless radio-frequency identification (RFID) sensing and identification system with switching reading

A chipless radio-frequency identification (chipless-RFID) and sensing system, where tags are read by proximity (near-field) through a switch, is presented. The tags consist of a set of identical resonant elements (split-ring resonators or SRRs), printed or etched at predefined and equidistant positions, forming a linear chain, each SRR providing a bit of information. The logic state ('1' or '0') associated with each resonator depends on whether it is present or not in the predefined position. The reader is an array of power splitters used to feed a set of SRR-loaded transmission lines (in equal number to the number of resonant elements, or bits, of the tag). The feeding (interrogation) signal is a harmonic (single-tone) signal tuned to a frequency in the vicinity of the fundamental resonance of the SRRs. The set of SRR-loaded lines must be designed so that the corresponding SRRs are in perfect alignment with the SRRs of the tag, provided the tag is positioned on top of the reader. Thus, in a reading operation, as long as the tag is very close to the reader, the SRRs of the tag modify (decrease) the transmission coefficient of the corresponding reader line (through electromagnetic coupling between both SRRs), and the amplitude of the output signal is severely reduced. Therefore, the identification (ID) code of the tag is contained in the amplitudes of the output signals of the SRR-loaded lines, which can be inferred sequentially by means of a switching system. Unlike previous chipless-RFID systems based on near-field and sequential bit reading, the tags in the proposed system can be merely positioned on top of the reader, conveniently aligned, without the need to mechanically place them across the reader. Since tag reading is only possible if the tag is very close to the reader, this system can be also used as a proximity sensor with applications such as target identification. The proposed chipless-RFID and sensing approach is validated by reading a designed 4-bit tag. For identification purposes, this system is of special interest in applications where a low number of bits suffice, and tag reading by proximity is acceptable (or even convenient). Applications mostly related to secure paper, particularly involving a limited number of items (e.g., exams, ballots, etc.), in order to provide authenticity and avoid counterfeiting, are envisaged. As a proximity sensor, the system may be of use in detecting and distinguishing different targets in applications such as smart packaging

Chipless labels detection by backscattering for identification and sensing applications

Chipless labels detection by backscattering for identification and sensing applications Détection d'étiquettes sans puce par rétrodiffusion pour des applications d'identification et de détectio

Chipless RFID sensor systems for structural health monitoring

Ph. D. ThesisDefects in metallic structures such as crack and corrosion are major sources of catastrophic failures, and thus monitoring them is a crucial issue. As periodic inspection using the nondestructive testing and evaluation (NDT&E) techniques is slow, costly, limited in range, and cumbersome, novel methods for in-situ structural health monitoring (SHM) are required. Chipless radio frequency identification (RFID) is an emerging and attractive technology to implement the internet of things (IoT) based SHM. Chipless RFID sensors are not only wireless, passive, and low-cost as the chipped RFID counterpart, but also printable, durable, and allow for multi-parameter sensing. This thesis proposes the design and development of chipless RFID sensor systems for SHM, particularly for defect detection and characterization in metallic structures. Through simulation studies and experimental validations, novel metal-mountable chipless RFID sensors are demonstrated with different reader configurations and methods for feature extraction, selection, and fusion. The first contribution of this thesis is the design of a chipless RFID sensor for crack detection and characterization based on the circular microstrip patch antenna (CMPA). The sensor provides a 4-bit ID and a capability of indicating crack width and orientation simultaneously using the resonance frequency shift. The second contribution is a chipless RFID sensor designed based on the frequency selective surface (FSS) and feature fusion for corrosion characterization. The FSS-based sensor generates multiple resonance frequency features that can reveal corrosion progression, while feature fusion is applied to enhance the sensitivity and reliability of the sensor. The third contribution deals with robust detection and characterization of crack and corrosion in a realistic environment using a portable reader. A multi-resonance chipless RFID sensor is proposed along with the implementation of a portable reader using an ultra-wideband (UWB) radar module. Feature extraction and selection using principal component analysis (PCA) is employed for multi-parameter evaluation. Overall, chipless RFID sensors are small, low-profile, and can be used to quantify and characterize surface crack and corrosion undercoating. Furthermore, the multi-resonance characteristics of chipless RFID sensors are useful for integrating ID encoding and sensing functionalities, enhancing the sensor performance, as well as for performing multi-parameter analysis of defects. The demonstrated system using a portable reader shows the capability of defects characterization from a 15-cm distance. Hence, chipless RFID sensor systems have great potential to be an alternative sensing method for in-situ SHM.Indonesia Endowment Fund for Education (LPDP

Design de circuitos RFID multi-ressonantes sem chip como substitutos dos códigos de barras

The chipless RFID technology , appears from an e ort to design low-cost RFID tags without the use of traditional silicone Application Specific Integrated Circuits (ASICs) that are the price bottleneck of the typicall RFID technology. In this way, tags become fully passive and without any active processing unit, thus the Chipless RFID system have more similarities with the Radio Detection And Ranging (RADAR) systems than with the common RFID systems. This dissertation sheds light on the problems and challenges that the RFID technology has as replacement of the optical barcode labels, discuss the state of the art of the chipless RFID technology and presents a model to describe the relationship between the multi-resonant circuit resonant frequency and the resonant spirals length. Finally, a chipless RFID system is simulated making use of the fractional Fourier Transform as means to separate linear frequency modulated signals that collide in both time and frequency domain. The results achieved with dissertation not only aid designers with the synthesis of multi-resonant circuits but also prove the reliability of the use of the fractional Fourier Transform as a means of manipulating the time-frequency domain and successfully recovering individual tags' ID from a signal containing more than one collided backscattered signal.A tecnologia de RFID sem chip, surgiu de um esforço para obter etiquetas RFID de baixo custo sem o uso de circuitos integrados de aplicação especifica (ASICs) que são a restrição à diminuição dos preço dos tipicos sistemas RFID. Desta forma, as tags tornam-se totalmente passivas e sem nenhuma unidade de processamento ativa, passando, os sistemas RFID sem chip a ter mais semelhanças com os sistemas de Radio Detection And Ranging (RADAR) do que com os sistemas RFID comuns. Esta dissertação esclarece os problemas e desafios que a tecnologia RFID enfrenta enquanto substituta das etiquetas de código de barras apresentando também o estado da arte da tecnologia RFID sem chip. Também apresenta e propõe um modelo para descrever a relação entre a frequência de ressonância do circuito multi-ressonante e o comprimento das espirais ressonantes. Finalmente, um sistema RFID sem chip é simulado usando a transformada fracionária de Fourier como meio de separar sinais modulados linearmente em frequência que colidem simultaneamente no domínio do tempo e da frequência. Os resultados alcançados com esta dissertação por um lado ajudam os projetistas com a síntese de circuitos multi-ressonantes e por outro provam a confiabilidade do uso da transformada fracionária de Fourier como um meio de manipular o domínio tempo-frequência para recuperar com sucesso informa ção individual de ID a partir de um sinal que contém mais de um sinal transmistido de uma etiqueta sem chip.Mestrado em Engenharia Eletrónica e Telecomunicaçõe

Applications of Antenna Technology in Sensors

During the past few decades, information technologies have been evolving at a tremendous rate, causing profound changes to our world and to our ways of living. Emerging applications have opened u[ new routes and set new trends for antenna sensors. With the advent of the Internet of Things (IoT), the adaptation of antenna technologies for sensor and sensing applications has become more important. Now, the antennas must be reconfigurable, flexible, low profile, and low-cost, for applications from airborne and vehicles, to machine-to-machine, IoT, 5G, etc. This reprint aims to introduce and treat a series of advanced and emerging topics in the field of antenna sensors

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

Improving the Manufacture by Flexographic Printing of RFID Aerials for Intelligent Packaging

Flexography is a well-established high-volume roll-to-roll industrial printing process that has shown promise for the manufacture of printed electronics for smart and intelligent packaging, particularly on to flexible substrates. Understanding is required of the relationship between print process parameters, including ink rheology, and performance of printed electronic circuits, sensors and in particular RFID antenna. The complexity of this printing process with its shear and extensional flows of complex inks and flexible substrates can lead to undesirable surface morphology to the detriment of electronic performance of the print. This thesis reports work that progresses the understanding of the complex relationships amongst relevant factors, particularly focusing on the printability of features that have an impact on printed RFID antenna where increases in resistance increase the antennas resonant frequency. Flexography was successfully used to print RFID antenna. However, the large variation in print outcomes when using commercial inks and the limits on resistivity reduction even at the optimal print parameters necessitated the systematic development of an alternative silver flake ink. Increases in silver loading and TPU polymer viscosity grade (molecular weight) increased the viscosity. The ink maintained its geometry from the anilox cell between rollers, on to the substrate and print surface roughness increased. This, however, did not increase resistance of the track due to the high silver loading. Better understanding of the relationship between print parameters, print outcomes, ink rheology and performance of an RFID antenna has been achieved. Increases in silver loading up to 60wt.% improved conductivity. However, further increasing the silver loading produced negligible additional benefit. An adaption of Krieger-Dougherty suspension model equation has been proposed for silver at concentrations over 60wt.% after assessing existing suspension models. Such a model has proven to better predict relative viscosities of inks than Einstein-Batchelor, Krieger-Dougherty and Maron-Pierce equations. Increasing TPU viscosity grade was found to be a promising ink adjustment in the absence of changing print parameters, to produce a more consistent print. Better prediction of ink behaviour will allow for improved control of ink deposition, which for RFID applications can improve ink conductivity, essential for good response to signal. Further developments such as addition of non-flake particles and formulation refinement are required to enable the model ink to match the resistivity of the commercial ink

Realistic chipless RFID: protocol, encoding and system latency

Chiplose Identifikation über Funkfrequenzen, RFID (engl., Radio Frequency IDentification) ist eine vielversprechende Technology, der man die Fähigkeit zuschreibt, in naher Zukunft den optischen Barcode zu ersetzen. Letztgenannter hat Einschränkungen durch i) RFID Tags sind bei nicht vorhandener Sichtverbindung (engl. Non-Line-Of-Sight, NLOS) auch nicht lesbar; ii) das Scannen der Barcodes benötigt in den meisten Fällen manuelles Eingreifen; iii) es ist unmöglich mehrere Barcodes gleichzeitig auszulesen; iv) und als Folge davon entsprechende Verzögerungen beim Auslesen größerer Mengen von Barcodes, da alle einzeln gescannt werden müssen. Die Beiträge der vorliegenden Dissertation konzentrieren sich auf drei Schwerpunkte von frequenzcodierten (engl. frequency coded, FC) chiplosen RFID Systemen. Der erste Schwerpunkt ist die gleichzeitige Identifikation von mehreren RFID Tags und kümmert sich um den Fall, dass sich mehrere RFID Tags in der Lesezone des RFID Lesegerätes befinden. Der zweite Aspekt betrifft die Verzögerung des Systems, die Zeit, das Lesegerät zum Identifizieren der RFID Tags benötigt. Und drittens die Coding Kapazität des Systems, sie ist verantwortlich für die zu erreichende Bittiefe des RFID Systems. Ein real umsetzbares RFID System erfordert Lösungen in allen drei Aspekten. Da chiplose RFID Tags keine integrierten Schaltungen (ICs) und somit auch keine Speicherbausteine besitzen, ist die Anzahl der auf dem RFID Tag speicherbaren Bits begrenzt. Und als Folge davon sind die Standards und Protokolle, die für die herkömmlichen chipbehafteten RFID Systeme entwickelt worden, nicht auf chiplose RFID Systeme übertragbar. Das wesentliche Ziel des ersten Beitrages ist die Einführung eines neuen Multi-Tag Antikollisionsprotokolls, das auf der Modulation der Notchposition (engl. Notch Position Modulation, NPM) und Tabellen (engl. Look-Up-Table, LUT) zur Bestimmung der Netzwerk- und MAC- Layer des chiplosen RFID Systems basiert. Die erste Generation der vorgeschlagenen Protokolls (Gen-1) baut auf einer Zweiteilung des zur Verfügung stehenden Spektrums auf. Im unteren Frequenzbereich, als Präambel Bandbreite bezeichnet, wird jedem RFID Tag seine individuelle Frequenzverschiebung übermittelt und im zweiten Bereich, der sogenannten Frame Bandbreite, ist die Identifikationsnummer (ID) des RFID Tags hinterlegt. Mit dieser Anordnung lässt sich jegliche Interferenz zwischen den verschiedenen RFID Tags unterbinden, da sich die Antworten der RFID Tags nicht gegenseitig überlagern. Die zweite Generation dieses Protokolls bringt eine Verbesserung sowohl bei der Coding Kapazität als auch bei der Nutzung des zur Verfügung stehenden Frequenzspektrums. Dies wird dadurch erreicht, dass die ID des RFID in einer Tabelle im Lesegerät gespeichert wird. Die individuelle Frequenzverschiebung dient dabei als Adresse für die gespeicherten IDs. Dieser Schritt vereinfacht die Komplexität der Struktur des RFID Tags signifikant, während gleichzeitig die Erkennungswahrscheinlichkeit erhöht wird. Des Weiteren werden die Key Performance Indikatoren untersucht um die Leistungsfähigkeit der Protokolle zu beweisen. Beide Protokollversionen werden modelliert und in einer Umgebung mit 10 chiplosen RFID Tags simuliert, um die Randbedingungen für die Entwicklung der RFID Tags und des RFID Lesegerätes zu ermitteln. Außerdem wird eine neuartige Testumgebung für ein MultiTag Ultra Breitband (engl. ultra wideband UWB) RFID System unter realen Testbedingungen basierend auf einem Software Defined Radio (SDR) Ansatz entwickelt. In dieser Testumgebung werden sowohl die gesendeten Signal als auch Detektierungstechniken, Leerraum Kalibrierung zur Reduzierung der Streustrahlung und die Identifikationsprotokolle untersucht. Als zweiter Schwerpunkt dieser Arbeit werden neue Techniken zur Reduzierung der Systemlaufzeit (engl. System Latency) eingeführt. Das Ziel dabei ist, die Zeit, die das RFID Lesegerät zum Erkennen aller in Lesereichweite befindlichen chiplosen FC RFID Tags braucht, zu verkürzen. Der Großteil der Systemlaufzeit wird durch das gewählte Frequenzscanverfahren, durch die Anzahl der Mittelungen zur Eliminierung der umgebenden Streustrahlung und durch die Dauer eines Frequenzsprungs bestimmt. In dieser werden dazu ein adaptives Frequenzsprungverfahren (engl. adaptive frequency hopping, AFH) sowie ein Verfahren Mittels adaptiver gleitender Fensterung (engl. adaptive sliding window, ASW) eingeführt. Das ASW Verfahren ist dabei im Hinblick auf die Identifizierung der RFID Tags nach dem Gen-1 Protokoll entwickelt, da es ein gleitendes Fenster zur Detektierung der Notches mit einer variablen Breite zum Auslesen der ID erfordert. Im Gegensatz dazu wird das Auffinden der im Gen-2 Protokoll verwendeten Notchpattern durch das AFH Verfahren verbessert. Dies wird über variable Frequenzsprünge, die auf die jeweiligen Notchpattern optimiert werden, erreicht. Beide Verfahren haben sich als effektiv sowohl im Hinblick auf die Systemlaufzeit als auch auf die Genauigkeit erwiesen. Das ASW und das AFH Verfahren wurden dazu in der oben erwähnten Testumgebung implementiert und mit dem klassischen Frequenzsprungverfahren, feste feingraduierte Frequenzschritte, verglichen. Die Experimente haben gezeigt, dass das vorgeschlagene AFH Verfahren in Kombination mit ASW zu einer beachtlichen Reduzierung der Systemlaufzeit von 58% führen. Das Ziel des dritten Schwerpunkts dieser Arbeit ist die Einführung einer neuartigen Technik zur Erhöhung der Informationsdichte (engl. Coding capacity) in einem chiplosen FC RFID Systems. Die hierfür vorgeschlagene Modulation der Notchbreite (engl. notch width modulation, NWM) ermöglicht die Kodierung von 4 Bits (16 Zuständen) pro Resonator in dem die Notchbreite und die dazugehörige Frequenzlage ausgenutzt werden. Für jeden Notch werden 150MHz Bandbreite reserviert, innerhalb derer das Codebit durch eine bestimmte Bandbreiten an unterschiedlichen Frequenzen bestimmt wird Cj ( fk,Bl). Das bedeutet, bei einer Arbeitsfrequenz im Bereich von 2–5 GHz können so 80 Bits realisiert werden. Des Weiteren wurde eine smarte Singulärwertzerlegung (engl. smart singular value decomposition, SSVD) Technik entwickelt, um die Notchbreite zu ermitteln und eine geringe Fehlerwahrscheinlichkeit zu garantieren. Die Nutzung von Blockcodes zur Behebung von Fehlern wurde untersucht, um den größtmöglichen Nutzen aus der so gewonnene Bittiefe zu erzielen. Als Folge konnte eine große Bittiefe mit einer hohen Lesegenauigkeit bei vereinfachtem Aufbau des Lesegeräts erzielt werden. Außerdem wurde eine neuartige RFID Tag Struktur entworfen, die bei einer Größe von 4× 5 cm2 eine Codedichte von 4 Bits/cm2 erreicht. Verschiedene RFID Tag Konfigurationen wurden erstellt und das neu eingeführte Codierungsverfahren mit Hilfe von elektromagnetischen (EM) Simulation und der bereits erwähnten Testplattform überprüft. Die erzielten Ergebnisse ermöglichen ein widerstandsfähiges RFID System in einer realen Umgebung. Alle vorgeschlagenen Beiträge sind durch analytische Modelle, Simulationen und Messungen auf mögliche Probleme und die Grenzen einer Realisierung unter realistischen Bedingungen geprüft worden.Chipless Radio Frequency IDentification (RFID) is a promising technology predicted to replace the optical barcode in the near future. This is due to several problematic issues i) the barcode cannot read Non-Line-Of-Sight (NLOS) tags; ii) each barcode needs human assistance to be read; iii) it is impossible to identify multiple tags at the same time; and iv) the considerable time delay in case of massive queues because different types of objects need to be serially scanned. The contributions included in this dissertation concentrate on three main aspects of the Frequency Coded (FC) chipless RFID system. The first one is the multi-tag identification, which deals with the existence of multiple tags in the reader’s interrogation region. The second aspect is the system latency that describes the time the reader needs to identify the tags. Finally, there is the coding capacity that is responsible for designing a chipless tag with larger information bits. The aim of these aspects is to realize a chipless RFID system. Since the chipless tags are memoryless as they do not include Integrated Circuits (ICs), the number of bits to be stored in the chipless tag is limited. Consequently, the current RFID standards and protocols designed for the chipped RFID systems are not applicable to the chipless systems. The main objective of the first contribution is to introduce novel multi-tag anti-collision protocols based on Notch Position Modulation (NPM) and Look-Up-Table (LUT) schemes determining the network and MAC layers of the chipless RFID systems. The first generation of the proposed protocol (Gen-1) relies on dividing the spectrum into two parts; the first one is the preamble bandwidth that includes a unique frequency shift for each tag. The second part is the frame bandwidth which represents the tag ID. The tag ID is obtained based on the predefined frequency positions, making use of the unique frequency shift. Consequently, the interference is avoided as there will not be any overlap between the tags’ responses. The second generation of the protocol (Gen-2) introduces an improvement in the spectrum utilization and coding capacity. This is realized by transferring the tag-ID to be stored in a table in the main memory of the reader (look-up-table). The unique shift of each tag represents the address of the tag’s ID. Therefore, the complexity of the tag structure will be significantly reduced with an enhanced probability of detection. Furthermore, the key performance indicators for the chipless RFID system are explored to validate the protocol’s performance. Both protocols are modeled and simulated to identify 10-chipless tags in order to set the regulations of the tag and reader design. Moreover, a novel real-world testbed for a multi-tag Ultra Wideband (UWB) chipless RFID system based on Software Defined Radio (SDR) is introduced. In this testbed, all the signaling schemes related to the transmitted signal, the detection techniques, the empty room calibration for the clutter removal process, and the identification protocols are applied. The aim of the second aspect is to introduce novel techniques that reduce the time required by the reader to identify the FC chipless RFID tags existent in the reader’s interrogation region. This time delay is called system latency. The main parameters that significantly affect the overall system latency are the frequency scanning methodology, the number of spectrum scanning iterations for the clutter removal process, and the hop duration. Therefore, the Adaptive Frequency Hopping (AFH) and the Adaptive Sliding Window (ASW) methodologies are proposed to meet the requirements of the FC chipless RFID tags. Regarding the ASW technique, it is suitable to identify the tags using the Gen-1 protocol which utilizes a sliding window (for detecting the notch) with an adaptive size to extract the tag’s-ID. The second adaptive methodology, AFH, can identify the tags with the Gen-2 protocol by using a variable frequency step that fits the corresponding notch patterns. These techniques are proven to be efficient for the chipless RFID systems with regard to latency and accuracy. Likewise, the designed AFH and ASW technique’s performance is compared to the classical Fixed Frequency Hopping (FFH) methodology with a fine frequency step to validate the accuracy of the proposed techniques. A real-world SDR based testbed is designed and the proposed adaptive algorithms as well as the classical FFH methodology are implemented. The experiments show that the proposed AFH combined with the ASW algorithms significantly reduce the system latency by 58%. The goal of the third aspect is to introduce a novel technique that increases the coding capacity of the FC chipless RFID system. The proposed Notch Width Modulation (NWM) scheme encodes 4 bits (16-combinations) per single resonator exploiting the notch bandwidth and its corresponding frequency position. Furthermore, each notch can reserve a window with a bandwidth of 150 MHz and inside this window the notch can obtain a certain bandwidth with a specific resonant frequency constructing the coding pairs Cj ( fk,Bl). Hence, 80-bits could be achieved at the operating frequency 2–5 GHz, preserving the operating frequency bandwidth. Also, a Smart Singular Value Decomposition (SSVD) technique is designed to estimate the notch bandwidth and to ensure a low probability of error. In addition, the utilization of a linear block code as an error correcting code is explored to make the best use of the obtained coding gain. Consequently, a high encoding efficiency and an accurate detection can be achieved in addition to a simplified reader design. Moreover, a novel 4× 5 cm2 tag structure is designed to meet the requirements of the NWM coding technique achieving a coding density of 4 bits/cm2. Different tag configurations are manufactured and validated by measurements using the SDR platform. The introduced coding methodology is conclusively validated using Electromagnetic (EM) simulations and real-world testbed measurements. The considered achievements for the proposed aspects offer a robust chipless RFID system that can be considered in real scenarios. Furthermore, all the proposed contributions are validated using analytical modeling, simulation and measurements in order to list their difficulties and limitations

Realistic frequency coded chipless RFID: physically modulated tags and refectarray readers

In letzter Zeit hat die chiplose RFID Technologie enorme Aufmerksamkeit im besonders kostenbewussten Markt für Objektidentifikation erregt. Allerdings befindet sich der aktuelle Stand der Technik auf einem konzeptionellen Niveau und leidet noch unter einer Menge Einschränkungen, die eine sofortige Verwendung der Technologie noch verhindern. Grundsätzlich lässt sich ein chiploses RFID System in drei Teile unterteilen, dem RFID Lesegerät, den verwendeten Antennen und dem RFID Tag. Der Beitrag der vorliegenden Dissertation zur Überwindung der erwähnten Einschränkungen liegt in innovativen physikalisch modulierenden RFID Tags und in der Weiterentwicklung des Antennensystems des RFID Lesegerätes. Dabei werden besonders die drei im Folgenden beschriebenen Aspekte betrachtet. Der erste Aspekt beschäftigt sich mit physikalisch linear modulierten RFID Tags. Dabei werden die RFID Tags mit einem Ultra Breitband (engl. ultra wideband, UWB) Signal bestrahlt und die auf dem RFID Tag aufgebrachten Resonatoren modulieren die Frequenz des Signals physikalisch. Dabei werden dem UWB Signal resonante Notches und/oder Peaks aufmoduliert, die sich in der Frequenzantwort des von der effektiven Rückstrahlfläche (engl. radar cross section, RCS) zurückgestrahlten Signals befindet. Hierfür sind vier innovative physikalisch modulierende RFID Tags, mit dem Ziel einer effektiveren Kodierung und maximalen Kodierungstiefe bei gleichbleibender Frequenzauslastung und RFID Tag Größe, entwickelt worden. Der erste RFID Tag besteht aus ineinander verschachtelten Ringresonatoren, wobei jeder Resonator ein Notch, also ein Bit, erzeugt. Der zweite RFID Tag arbeitet auf zwei unterschiedlichen Polarisationsebenen für empfangene und rückgestrahlte Signale. Dadurch kann die Streustrahlung der Umgebung leichter herausgefiltert werden. Beide Strukturen sind skalierbar, druckbar und kompakt. Als drittes wird ein neuartiger Notchbreiten modulierender (engl. notch width modulation, NWM) RFID Tag eingeführt. Dabei ist die ID des RFID Tags nicht nur über die Notchlage im Frequenzbereich sondern auch über die Notchbreite definiert. Die Notchbreite stellt also eine zusätzliche Dimension bereit, die die Freiheitsgrade (engl. degree of Freedom, DoF) für Kodierung und Modulation erhöhen, was wiederum die kodier Effektivität und Codetiefe verbessert. Als letztes wird ein neuartiger On Off-Notch/Peak (OONP) und Notch/Peak-Position (N/P-P) modulierender RFID Tag eingeführt. Die Idee dahinter ist, sowohl das kopolarisierte als auch das kreuzpolarisierte Rückstrahl Signal eines mit einer linear-polarisierten Welle angeregten RFID Tags auszunutzen. Dies bittet ein weiteres Kriterium um sowohl kodier Effektivität als auch Codetiefe des chiplosen RFID Systems weiter zu verbessern. Gleichzeitig verbessert die kreuzpolarisierte Antwort auch wieder die Detektion des RFID Tags in einer realen Umgebung. Alle vorgeschlagenen RFID Tags und Modulationsschemata sind mit elektromagnetischen (EM) Simulationen und in einer realen Testumgebung überprüft worden. Der zweite Aspekt dieser Arbeit schlägt Reflect-Array Antennen (RA) für das RFID Lesegerät mit dem Ziel vor, die Lesereichweite zu erhöhen und die Reflektionen an der Umgebung zu minimieren. Das RA bietet dabei im Vergleich zu herkömmlichen Phased-Array-Antennen eine Menge weiterer Eigenschaften. Das RA ist einfach zu integrieren, von geringem Gewicht, hat eine sehr geometrische Anordnung und ist preiswert, um nur einige zu nennen. Insgesamt wurden drei neuartige RA Aufbauten entwickelt. Als erstes wurde eine logarithmisch periodische Antenne (engl. log periodic antenna array, LPDA) als Primärstrahler für die entworfene RA Oberfläche genutzt. Der Prototype arbeitet bei 5.8GHz und erreicht eine Bandbreite von 300MHz. Außerdem ist der erzeugte Antennenstrahl viermal schmaler als der Primärstrahl und erreicht somit einen um 6dB höheren Antennengewinn bei einem Nebenkeulenpegel (engl. side lobe level, SSL) von −10dB. Für den zweiten Prototypen wird ein selbstentwickelter Hornstrahler mit konstanter Phase als Primärstrahler für die RA Oberfläche verwendet. Durch diese Anordnung wird ein UWB RA realisiert, mit dem mehrere Bits gleichzeitig ausgelesen werden können. Die Antenne arbeitet zwischen 4 − 6GHz und erreicht einen Öffnungswinkel (engl. half power beam width, HPBW) von 15° bei 19dBi Antennengewinn und −10dB SLL. Im Zusammenspiel mit den physikalisch modulierenden RFID Tags konnte mit diesem UWB RA eine Lesereichweite von 1m erzielt werden, was nach meinem Kenntnisstand die größte bisher für ein chiploses frequenzkodiertes (engl. frequency coded, FC) RFID System erreichte Lesereichweite in einer realen Innenraum Umgebung darstellt. Weiter wird eine dual polarisierte RA Antenne mit geringem Kreuzpolarisations Pegel vorgestellt. Es wird vorgeschlagen diese Antenne mit den ko-/kreuzpolarisierten RFID Tags zu verwenden. Als letztes wird eine RA Antenne mit elektronischer Strahlsteuerung eingeführt, die die Stabilität des Lesevorgangs weiter erhöht und eine präzise Ortung der chiplosen RFID Tags ermöglicht. Dazu wird eine Zelle vorgeschlagen, die mit Hilfe einer Varaktordiode in der Lage ist, für einzelne Frequenzen die Phase des reflektierten Signals elektronisch zu steuern. Ein Scanbereich von ±50° kann damit abgedeckt werden. Als dritter Aspekt werden nicht-lineare physikalisch modulierende RFID Tags vorgeschlagen. Hier ist der Kerngedanke, dass der RFID Tag seine ID mit einer anderen Frequenz zurückstrahlt als die mit der er selber angestrahlt wird. Durch dieses nichtlineare Verhalten wird die Umgebungsstrahlung komplett ausgeblendet, die sonst unumgänglichen Kalibrierungsmessungen werden überflüssig, das Problem der Verstimmung durch das RFID Tag Material wird umgangen und die Abdeckung wird erhöht. Die Nicht-Linearität wird durch eine einzige in die Struktur des RFID Tags integrierte Diode erzeugt. Zunächst werden RFID Tags vorgeschlagen, die mit Nichtlinearitäten zweiter Ordnung arbeiten. Für diese Kategorie werden drei unterschiedliche RFID Tags entworfen. Als Erstes ein Einzelton harmonischer RFID Radar Tag. In dieser Klasse strahlt das RFID Lesegerät einige spezifische Grundtöne aus, die schmalbandige Empfangsan-tenne des RFID Tags ist auf einen Grundton abgestimmt, den sie an die Diode weiterleitet. Die hier generierte zweite Harmonische wird von der entsprechend konfigurierten Sendeantenne der RFID Tags zurückgestrahlt. Dabei gilt, je schmaler der Bandbassfilter, desto mehr Frequenzen können zur Kodierung genutzt werden. Um die Codekapazität zu erhöhen werden als nächsten Mehrfrequenzabfragen vorgestellt. Dazu werden am RFID Lesegerät nacheinander, um keine Mischprodukte entstehen zu lassen, vordefinierte Frequenzen durchlaufen. Auf dem RFID Tag können jetzt mehrere ID Bits wieder durch die unterschiedlichen Frequenzen der jeweiligen zweiten Harmonischen erzeugt werden (engl. Notch Position Modulation, NPM). Anschließend werden festdefinierte Frequenzpaare zum Auslesen der ID verwendet. Die Diode mischt beide Frequenzen und antwortet nur auf der Mischfrequenz eines der Frequenzpaare. In einer weiteren Kategorie werden die Intermodulationseigenschaften der dritten Ordnung ausgenutzt, mit dem Vorteil, dass nur ein relativ geringer Frequenzbereich benötigt wird. Hierbei wir der RFID Tag mit zwei benachbarten Frequenzen bestrahlt und die zurückgestrahlte Intermodulationsfrequenz stellt die ID des RFID Tags dar. Schließlich wird die Kodierung über die Phaseninformation vorgestellt. Zusätzlich zur Existenz oder Fehlen eines Peaks oder Notches wird der dazuge- hörige relative Phasenzustand zur Kodierung herangezogen. Alle vorgestellten RFID Tags und ihre Modulation werden an Hand von Harmonische-Balance-Analyse, EM Simulationen und Messungen in einer realen Testumgebung überprüft. Zum Schluss lässt sich sagen, die einzigartigen Eigenschaften, die in der vorliegenden Dissertation betrachtet werden, bringen wesentliche Verbesserungen für den Einsatz von chiplosen RFID Systemen.Recently, the chipless Radio Frequency Identification (RFID) technology has attracted tremendous attention in the market of item identification where the cost is the main concern. However, up to date the technology is at the conceptual level and suffers from a lot of imitations that hinder the technology deployment. The chipless RFID system comprises three major parts which are the reader circuit, the interrogation antennas, and the chipless tags. The contributions of this dissertation are to overcome the challenges that impede the deployment of the chipless RFID system from the perspective of innovating physically modulated tags and developing the reader antenna system. In particular, the system is considered in three novel aspects. The first aspect is the linear physically modulated tags where the tag is interrogated by Ultra Wideband (UWB) signal and the tag inscribed metallic resonators are physically modulating the interrogation frequencies. Therefore, the UWB waveform is modulated in the form of resonant notches, and/or peaks that are inherently embedded in the tag backscattered Radar Cross Section (RCS) frequency response. In this regard, four innovative physically modulated tags are developed aiming at enhancing the coding efficiency, maximizing the coding capacity, conserving the operating frequency range and preserving the tag size. The first tag is based on nested circular ring resonators where each resonator codifies a tag coding notch. Terefore, the tag structure is scalable, printable and compact size. Moreover, a novel encoding methodology is employed to preserve the notch width and position while coding. The second developed tag is a depolarizing one where the polarization isolation between the reader interrogation signal and the tag response is utilized to minimize the environmental clutter reflections. Furthermore, the tag is scalable, printable, and compact size in the credit card format. Thirdly, a novel Notch Width Modulation (NWM) tag is introduced where the tag-ID is not only based on the notch position but also on the notch width. Hence, the notch width configures a further dimension to increase the Degree of Freedom (DoF) for coding and modulation. Therefore, the notch width and position are modulated simultaneously aiming at enhancing the coding efficiency and capacity. Lastly, a novel On Off Notch/Peak (OO-N/P) and Notch/Peak-Position (N/P-P) modulation tag is introduced. The tag basic idea is to exploit both the co-polarized and cross polarized backscattered signals from a tag excited with a linear polarized wave. Consequently, the tag signature is encoded into Notch/Peak (N/P) format in two orthogonal planes. Thus, the Co/Cross-polarizing N/P modulation scheme presents a novel criterion for enhancing the coding efficiency and capacity of the chipless RFID systems. Moreover, the cross-polarized response enhances the tag detection in a realistic environment. The proposed tags and their associated physical modulation schemes are validated using Electro Magnetic (EM) simulations and real-world testbed measurements. In the second aspect, the Reflectarray (RA) antenna is proposed to be utilized in the reader side aiming at increasing the reading range, minimizing the environmental reflections, and acquiring a lot of novel capabilities that can not be provided by the conventional antenna arrays. The spatial feeding RA antenna is easily integrated with the RF circuits, lightweight, conformal geometry, and low cost. Hence, in this concern, three different novel designs are developed. The first design utilizes the Log Periodic Array (LPDA) antenna to feed the developed RA surface. This introduced prototype operates at 5.8GHz and achieves 300MHz bandwidth. Moreover, the RA antenna radiation beam is 4 times narrower than the feeder beam and thus 6dB higher in gain with −10dB Side Lobe Level (SLL). The second developed prototype uses a constant phase center horn antenna to feed the RA surface. Thus, an UWB RA antenna enabling multiple bits accommodation is designed. This antenna operates from 4GHz to 6GHz with 15° Half Power Beam Width (HPBW), 19dBi gain, and −10dB SLL. Furthermore, this developed UWB RA antenna is successfully integrated with the physically modulated tags and a reading range of 1m is achieved. To the best of my knowledge, this is the highest reading range achieved in the Frequency Coded (FC) chipless RFID systems, considering real-world indoor environment and software defined radio reader. After that, dual-polarized RA antenna with low cross-polarization level is presented. This RA antenna is proposed to be utilized with the Co/Cross-polarizing tags. Finally, a successful implementation of an electronic beam steering RA antenna is introduced. This novel beam steering RA antenna system enhances the reading robustness and can precisely locate the chipless tags. In this concern, a novel unit cell that is able to electronically control the reflected phase at different discrete frequencies utilizing a single varactor diode is proposed. Therefore, a scanning range of ±50° is achieved. Moreover, the steered beams are 4 times narrower than the feeder beam and thus 4 times higher in gain. In the third aspect, the nonlinear physically modulated tags are proposed. The core functionality relies on interrogating the tag with a prescribed set and format of frequencies in a time regulated technique while the tag replies with its unique ID at other frequencies. Therefore, the nonlinearity is exploited to completely isolate the environmental clutter reflections, get rid of the necessary reference calibration measurements, overcome the detuning caused by the tagged item materials, and increase the coverage. These objectives are attained by exploiting the nonlinearity generated from a single unbiased diode integrated with the tag structure. The first proposed tag category relies on exploiting the second order nonlinear terms. Therefore, in this regard, three novel tags are introduced. The first class is the single tone harmonic radar tags. In this class, the reader scans the available tags by sending specific fundamental tones. Then, the tag receiving antenna is tuned at only one of these fundamentals which is maximally conveyed to the nonlinear device for generating the corresponding harmonics. Consequently, the tag transmitting antenna is tuned at the second harmonic which is retransmitted back towards the reader representing the tag-ID. Thus, the narrower is the band-pass filter provided by the tag receiving antenna or integrated into it, the more the frequencies that can be utilized for coding. After that, the multi-tone interrogation is proposed to increase the coding capacity. Hence, the tag is interrogated with a prescribed set of fundamentals that are swept over the time to avoid the generation of the mixing products in the reader and tag as well. The tag in turn which is completely planar based on the Coplanar Waveguide (CPW) technology implements a Notch Position Modulation (NPM) scheme in the second harmonics of these fundamental tones. Therefore, the notches that are existing in the second harmonic response symbolize the tag-ID. Afterward, the simultaneous multi-tone interrogation is explored. In this concern, a set of distinct frequency pairs are used to interrogate the nonlinear tags. As a consequence, these tones are mixed through the nonlinear device. Consequently, the tag transmitting antenna figures out only one of these mixed products. The second proposed tag category relies on exploiting the inter-modulation communication principle which exhibits a small frequency span. Therefore, the tag is illuminated by two co-located frequencies and respond at an inter-modulated frequency which is retransmitted by the tag transmitting antenna representing the tag-ID. Finally, the phase encoding capability is proposed. Therefore, not only the existence or the non-existence of a harmonic notch or peak used in coding the tag-ID but also the corresponding relative phase states can be considered. The introduced tags and their associated physical modulation schemes are verified using harmonic balance analysis, EM simulations and realistic testbed measurements. Lastly, the unique features which are considered in the dissertation bring a significant enhancement to the deployment of the chipless RFID system

Dense and long-term monitoring of Earth surface processes with passive RFID -- a review

Billions of Radio-Frequency Identification (RFID) passive tags are produced yearly to identify goods remotely. New research and business applications are continuously arising, including recently localization and sensing to monitor earth surface processes. Indeed, passive tags can cost 10 to 100 times less than wireless sensors networks and require little maintenance, facilitating years-long monitoring with ten's to thousands of tags. This study reviews the existing and potential applications of RFID in geosciences. The most mature application today is the study of coarse sediment transport in rivers or coastal environments, using tags placed into pebbles. More recently, tag localization was used to monitor landslide displacement, with a centimetric accuracy. Sensing tags were used to detect a displacement threshold on unstable rocks, to monitor the soil moisture or temperature, and to monitor the snowpack temperature and snow water equivalent. RFID sensors, available today, could monitor other parameters, such as the vibration of structures, the tilt of unstable boulders, the strain of a material, or the salinity of water. Key challenges for using RFID monitoring more broadly in geosciences include the use of ground and aerial vehicles to collect data or localize tags, the increase in reading range and duration, the ability to use tags placed under ground, snow, water or vegetation, and the optimization of economical and environmental cost. As a pattern, passive RFID could fill a gap between wireless sensor networks and manual measurements, to collect data efficiently over large areas, during several years, at high spatial density and moderate cost.Comment: Invited paper for Earth Science Reviews. 50 pages without references. 31 figures. 8 table