Development of embedded modulated scatterer technique: single- and dual-loaded scatterers

Health monitoring of infrastructure is an important ongoing issue. Therefore, it is important that a cost-effective and practical method for evaluating complex composite structures be developed. A promising microwave-based embedded sensor technology is developed based on the Modulated Scatterer Technique (MST). MST is based on illuminating a probe, commonly a dipole antenna loaded with a PIN diode (also referred to as a single-loaded scatterer, or SLS), with an electromagnetic wave. This impinging wave induces a current along the scatterer length, which causes a scattered field to be reradiated. Modulating the PIN diode also modulates the signal scattered by the probe, resulting in two different states of the probe. By measuring this scattered field, information about the material in the vicinity of the probe may be determined. Using the ratio of both states of the probe removes the dependency of MST on several measurement parameters. In order to separate the scattered signal from reflections from other targets present in the total detected signal, a swept-frequency measurement process and subsequent Fourier Transform (time-gate method) was incorporated into MST. Additionally, a full electromagnetic study of the SLS, as applied to MST, was also conducted. The increased measurement complexity and data processing resulting from the time-gate method prompted the development of a novel dual-loaded scatterer (DLS) probe design, with four possible modulation states. By taking a differential ratio, the reflections from other targets can be effectively removed, while preserving the measurement parameter independence of the SLS ratio. A full electromagnetic derivation and analysis of the capabilities of the DLS as applied to MST is included in this investigation, as well as representative measurements using the DLS probe --Abstract, page iii

Novel modulated antennas and probes for millimeter wave imaging applications

Microwave and millimeter wave (300 MHz - 300 GHz) imaging techniques have shown great potential for a wide range of industrial and medical applications. These techniques are fundamentally based on measuring relative and coherent electromagnetic fields distributions, e.g., electric fields, around the object to be imaged. Various imaging systems can be devised for measuring relative electric field distributions; each with it own advantages and limitations. This dissertation is focused on addressing critical challenges related to the practical implementation of various microwave and millimeter wave imaging systems. Specifically, this research is meant to achieve three main objectives related to designing efficient modulated imaging methods/array elements, reducing the sensitivity to standoff distance variations in near-field imaging, and designing a simple and accurate vector network analyzer (VNA) for in-situ imaging applications. The concept of modulating millimeter wave antenna and scatterer structures, directly to increase the overall system sensitivity and reduce the image acquisition time, is central to the development presented herein. To improve upon the conventional modulated scatterer technique (MST) based on dipole scatterers; a new multiple loaded scatterer (MLS) method and novel loaded elliptical slot are introduced and analyzed. A unique near-field differential probe based on dual-loaded modulated single waveguide aperture is developed to compensate for and reduce the effect of standoff distance variations in near-field imaging. Finally, a novel vector network analyzer (VNA) design is introduced to meet the rising need for in-situ vector measuring devices. To realize a robust handheld millimeter wave VNA, a custom-designed waveguide phase shifter based on sub-resonant loaded slots is introduced. The proposed MLS method, modulated elliptical slot, dual-loaded modulated aperture probe, and VNA are thoroughly investigated and their efficacy for microwave and millimeter wave imaging is demonstrated --Abstract, page iii

RFID multiantenna systems for wireless communications and sensing

Many scientific, industrial and medical applications require the measurement of different physical parameters in order to collect information about the spatially distributed status of some process. Very often this information needs to be collected remotely, either due to the spatial dispersion of the measurement points or due to their inaccessibility. A wireless embedded self-powered sensor may be a convenient solution to be placed at these inaccessible locations. This thesis is devoted to study the analytical relation governing the electromagnetic coupling between a reader and a embeddable self-powered sensor, based on radio frequency identification (RFID) technology, which is capable of wirelessly retrieving the status of physical parameters at a remote and inaccessible location. The physical parameter to be sensed may be the electromagnetic (EM) field existing at that location (primary measurement) or the indirect measurement of other parameters such as the temperature, humidity, etc. (secondary measurement). Given the simplicity of the RFID solution (highly embeddable properties, scavenging capabilities, penetration and radio coverage characteristics, etc.) the measurement can be done at a single location, or it can be extended to a set of measuring locations (an array or grid of sensors). The analytical relation is based on a reciprocity formulation studying the modulation of the scattered field by the embedded sensor in relation with the incident field, and allows to define a set of quality parameters of interest for the optimum design of the sensors. Particular attention is given to the scavenging circuitry as well as to the antenna design relevant to the sensing objective. In RFID tags, the existence of an RF harvesting section is an improvement with respect to conventional scattering field probes since it removes the need of DC biasing lines or optical fibers to modulate the sensor. However, this harvesting section introduces non-linearities in the response of the sensor, which requires a proper correction to use them as EM-field probes, although the characterization of the non-linearities of the RFID tag cannot be directly done using a conventional vector network analyzer (VNA), due to the requirements of an RFID protocol excitation. Due to this, this thesis proposes an alternative measurement approach that allows to characterize the different scattering states used for the modulation, in particular its non-linear behavior. In addittion, and taking this characterization as the starting point, this thesis proposes a new measurement setup for EM-field measurements based on the use of multiple tones to enlarge the available dynamic range, which is experimentally demonstrated in the measurement of a radiation pattern, as well as in imaging applications. The RFID-based sensor response is electromagnetically sensitive to the dielectric properties of its close environment. However, the governing formulation for the response of the probe mixes together a set of different contributions, the path-loss, the antenna impedance, the loads impedance, etc. As a consequence, it is not possible to isolate each contribution from the others using the information available with a conventional RFID sensor. This thesis mathematically proposes and experimentally develops a modification of the modulation scheme to introduce a new set of multi-load scattering states that increases the information available in the response and properly isolate each term. Moreover, this thesis goes a step forward and introduces a new scattering state of the probe sensitive to temperature variations that do not depend on the environment characteristics. This new configuration enables robust environmental sensing in addition to EM-field measurements, and sensing variations of the dielectric properties of the environment

Experimental performance evaluation and design of schemes for passive RFID network

Passive Radio Frequency Identification (RFID) is a short range technology for transferring information. The main advantage of passive RFID systems over active communication systems is the battery-less operation at the client sides. However, there are two major challenges that limit the widespread adaptation of passive RFID systems: short communication range and low read rate in dense deployments. This dissertation addresses these issues by studying the root causes and develops solutions for them. In this dissertation, understanding the backscattering behavior of antennas and also the mutual coupling interactions among them are found to be the root causes of the two above-mentioned challenges for RFID networks. Thus, by studying these two main root causes solutions for them are proposed, investigated and verified, by simulations and measurements. The contributions in this dissertation include: (1) Design of a new measurement technique to estimate the structural scattering coefficient of a linear antenna. (2) Showing that the well-known Green model cannot completely explain the variation of the radar cross section of a T-match bowtie antenna over its Г plane. (3) Introducing dual loading in designing RFID antenna tags to: (a) Increase the vector differential backscattering signal, (b) Produce higher order modulations. (4) Introducing a new state for RFID tags in that tags switch to a low scattering states to: (a) suppress their interference to a target antenna in the network. (b) Stabilize the RCS of the target antenna. (c) Increase read rate in RFID networks. (5) Numeric analysis of the mutual coupling impedance for two side by side scattering antennas. (6) Introducing a multi-port RFID which can switch to different load impedances to help a target antenna in its vicinity increase its signal over the level when the target is alone in the field --Abstract, page iv

Radar Testbed Characterization for Evaluation of Modulated Scatterer Concepts

The following research explores the concepts of communication-embedded radar with an emphasis on radar operation and modulated scatterer concepts. Once firmly established the concept of communication via radar backscatter could be used in a variety of fields including, mass data collection, SAR calibration, and military communication. A radar testbed was developed and charactersized to enable experimental evaluation of communication via modulated scatterer concepts. The radar operates with a 1.84-GHz center frequency and 75-MHz bandwidth (later upgraded to a 235-MHz bandwidth). A dual-channel arbitrary waveform generator is loaded with used-defined complex baseband signals for frequency upconversion for transmission via a 22 dBi parabolic reflector antenna. Backscattered signals are received and frequency downconverted on four identical channels, each fed by a dipole antenna. A 4-channel data acquisition system digitizes and records the output video signal at 1-GSa/s per channel for signal analysis. The primary means of evaluating the radar testbed were loopback and freespace setups. The loopback setup consisted of a cabled inserted between transmitter and receiver to provide a controlled propagation environment. In this setup results were shown to be desirable, and easily explained by theory. Linear FM (chirp) waveforms were used which enabled pulse compression to reduce the peak signal power while preserving range resolution. After pulse compression via matched filter routines, amplitude, phase, and resolution were characterized and found to agree with theory. In extending the tests to freespace, it was seen that near targets could be seen and resolved coherently across the 4 channels. A prototype modulated scatterer constructed by a senior design group was further tested to evaluate the prototype's viability. This scatterer impresses a bit sequency on the radar wavefrom by modulating the scatterer's termination impedance between an open and short circuit at a rate determined by the bit sequence to be communicated (similar to frequency-shift keying). Connected via a cabled-loopback configuration, the prototype was shown to impress a bit sequence onto the backscatter of the transmit chirp and, through processing, the bit stream associated with the modulated scatterer was decoded successfully. Followon testing will evaluate freespace operation and techniques for decoding information from multiple devices in the field of view. This radar testbed will be used to experiementally evaluate various modulated scatterer concepts as well as other radar-related waveform and signal processing concepts in the future

2008 Index IEEE Transactions on Control Systems Technology Vol. 16

This index covers all technical items - papers, correspondence, reviews, etc. - that appeared in this periodical during the year, and items from previous years that were commented upon or corrected in this year. Departments and other items may also be covered if they have been judged to have archival value. The Author Index contains the primary entry for each item, listed under the first author\u27s name. The primary entry includes the coauthors\u27 names, the title of the paper or other item, and its location, specified by the publication abbreviation, year, month, and inclusive pagination. The Subject Index contains entries describing the item under all appropriate subject headings, plus the first author\u27s name, the publication abbreviation, month, and year, and inclusive pages. Note that the item title is found only under the primary entry in the Author Index

2009 Index IEEE Antennas and Wireless Propagation Letters Vol. 8

This index covers all technical items - papers, correspondence, reviews, etc. - that appeared in this periodical during the year, and items from previous years that were commented upon or corrected in this year. Departments and other items may also be covered if they have been judged to have archival value. The Author Index contains the primary entry for each item, listed under the first author\u27s name. The primary entry includes the coauthors\u27 names, the title of the paper or other item, and its location, specified by the publication abbreviation, year, month, and inclusive pagination. The Subject Index contains entries describing the item under all appropriate subject headings, plus the first author\u27s name, the publication abbreviation, month, and year, and inclusive pages. Note that the item title is found only under the primary entry in the Author Index

Non-Invasive Near-Field Measurement Setup Based on Modulated Scatterer Technique Applied to Microwave Tomographhy

Résumé L’objectif principal de cette thèse est d’aborder la conception et le développement d’un montage d’imagerie en champ proche (CP) basé sur la technique de diffusion modulé (TDM). La TDM est une approche bien connue et utilisée pour des applications où des mesures précises et sans perturbations sont nécessaire. Parmi les applications possibles disponibles pour la fabrication d’une sonde TDM, que ce soit électrique, optique, mécanique, le diffuseur optique modulé DOM a été pris en considération afin de fournir des mesures quasi sans-perturbations en raison de l’invisibilité des fibres optiques face aux champs radiofréquence électromagnétiques. La sonde est composée d’une puce photodiode commerciale “off-the-shelf” (dispositif non-linéaire), d’une antenne dipôle courte agissant comme diffuseur et un réseau d’adaptation (cir¬cuit passif). Cet dernieér améliore les propriétés de diffusion et augmente également la sensibilité de la sonde DOM dans la bande de fréquence pour laquelle le réseau correspondant est optimisé. Les caractéristiques de rayonnement de la sonde, y compris sa réponse de polarisation croisée et sa sensibilité omnidirectionnelle, ont été théoriquement et expérimentalement étudiés. Enfin, la performance et la fia¬bilité de la sonde a été étudiée en comparant des mesures de distribution de champs proche avec une distribution de champs simulé. Une vitesse d’imagerie accrue a été obtenue utilisant un réseau de sondes DOM, ce qui réduit les mouvements mécaniques résultant ansi en une amélioration remarquable de la vitesse de mesure. Le couplage mutuel, le temps de commutation et l’effet d’obscurité, des effets qui peuvent affecter les performances du réseau ont été explorés. Ensuite, les résultats obtenus par le réseau ont été validé par une imagerie CP en mesurant la distribution des champs E d’une antenne sous test (AST) et la comparant à des résultats de simulation. Une calibration et un calcul de moyenne ont été appliqués à des données brutes pour com¬penser pour les incertitudes dans la fabrication et l’interaction entre réseau/AST et réseau/antenne de réception. La plage dynamique et la linéarité de la réponse de l’imagerie CP ont été améliorées en ajoutant un circuit suppresseur de porteuse en avant de l’antenne. Le suppresseur élimine la porteuse sur laquelle aucune information n’est transmise et laisse les bandes latérales intactes.----------Abstract The main focus of this thesis is to address the design and development of a near-field (NF) imaging setup based on the modulated scatterer technique (MST). MST is a well-known approach used in applications where accurate and perturbation-free mea¬surement results are necessary. Of the possible implementations available for making an MST probe, including electrical, optical and mechanical, the optically modulated scatterer OMS was considered in order to provide nearly perturbation-free measure¬ment due to the invisibility of optical fiber to the radio-frequency electromagnetic fields. The OMS probe consists of a commercial, off-the-shelf (COTS) photodiode chip (nonlinear device), a short-dipole antenna acting as a scatterer and a match¬ing network (passive circuit). The latter improves the scattering properties and also increases the sensitivity of the OMS probe within the frequency range in which the matching network is optimized. The radiation characteristics of the probe, includ-ing cross-polarization response and omnidirectional sensitivity, were both theoreti¬cally and experimentally investigated. Finally, the performance and reliability of the probe was studied by comparing measured near-field distributions on a known field distribution with simulations. Increased imaging speed was obtained using an array of OMS probes, which re¬duces mechanical movements. Mutual-coupling, switching time and shadowing effect, which all may affect the performance of the array, were investigated. Then, the re¬sults obtained by the array were validated in a NF imager by measuring the E-field distribution of an antenna under test (AUT) and comparing it with a simulation. Cal¬ibration and data averaging were applied to raw data to compensate the probes for uncertainties in fabrication and interaction between array/AUT and array/receiving antenna. Dynamic range and linearity of the developed NF imager was improved by adding a carrier canceller circuit to the front-end of the receiver. The canceller eliminates the carrier on which no information is transmitted and leaves the sidebands intact. This enables us to increase the amplification gain to achieve better signal-to-noise ratio (SNR) and more importantly to expand the imager’s dynamic range

Characterization and Design Methodologies for Wearable Passive UHF RFID Tag Antennas for Wireless Body-Centric Systems

Radio Frequency Identification (RFID) is a wireless automatic identification technology that utilizes electrically active tags – low-cost and low-power wireless communication devices that let themselves transparently and unobstructively be embedded into everyday objects to remotely track information of the object’s physical location, origin, and ownership. At ultra-high frequencies (UHF), this technology uses propagating electromagnetic waves for communication, which enables the fast identification of tags at large distances. A passive RFID tag includes two main components; a tag antenna and an RFID integrate circuit (tag IC). A passive tag relies solely on the external power harvested from an incident electromagnetic wave to run its circuitry and for data transmission. The passiveness makes the tag maintenance-free, simple, and low-cost, allowing large-scale commercial applications in the supply chain, ticketing, and asset tracking. The future of RFID, however, lies in the transition from traditional embedded applications to wearable intelligent systems, in which the tags are seamlessly integrated with everyday clothing. Augmented with various ambient and biochemical sensors, the tag is capable of detecting physical parameters of its environment and providing continuous monitoring of human vital signs. Tremendous amount of tagged entities establish an intelligent infrastructure that is personalized and tailored to the needs of each individual and ultimately, it recedes into the background of our daily life. Although wearable tags in intelligent systems have the enormous potential to revolutionize the quality of human life, the emerging wearable RFID applications introduce new challenges for designers developing efficient and sophisticated RFID systems. Traditional tag design parameters and solutions will no longer respond to the new requirements. Instead, the whole RF community must adopt new methods and unconventional approaches to achieve advanced wearable tags that are highly transparently integrated into our daily life. In this research work, an empirical as well as a theoretical approach is taken to address the above-mentioned wearable RFID tag challenges. Exploiting new analysis tools in combination with computational electromagnetics, a novel technique to model the human body in UHF applications for initiating the design of optimized wearable tags is developed. Further, fundamental unprecedented UHF characteristics of advanced wearable electronics materials – electro-textiles, are established. As an extremely important outcome of this research work, innovative optimization methodologies for the promotion of novel and advanced wearable UHF antennas are proposed. Particularly, it is evidenced that proper embroidery fabrication techniques have the great potential to realize wearable tag antennas exhibiting excellent RF performance and structural properties for the seamless integration with clothing. The kernel of this research work is the realization of a flexible and fully embroidered passive UHF RFID patch tag prototype achieving optimized performance in close vicinity of the high-permittivity and dissipative human body. Its performance may be considered as a benchmark for future wearable antenna designs. This shows that this research work outcome forms an important contribution to the state of the art and a milestone in the development towards wearable intelligence