La RFID sans puce, en raison du très faible coût des tags, a ouvert une nouvelle voie pour les systèmes d'identification. Les étiquettes RFID sans puce fonctionnant dans le domaine temporel ont l'avantage d'être compatibles avec de grandes distances de lecture, de l'ordre de quelques mètres, et de pouvoir fonctionner dans les bandes de fréquence ISM. Cependant, les tags de ce type développés jusqu'à lors n'offraient qu'une faible capacité de codage. Cette thèse propose une nouvelle méthode pour augmenter la capacité de codage des tags fonctionnant dans le domaine temporel en utilisant des C-sections, c'est-à-dire des lignes de transmission repliées de manière à avoir des zones fortement couplées, ce qui leur donne un caractère dispersif. Une autre approche basée sur une technique multi-couches a également été introduite de façon à augmenter considérablement la capacité de codage. Pour terminer, la preuve de concept d'un tag-capteur d'humidité, basé sur l'utilisation de nano fils de silicium, est également présentée. / Chipless RFID tags, owing to their low cost, have opened a new way to the identification systems. Chipless RFID tags operating in the time domain have the advantage of being compatible with large reading distances of the order of a few meters, and also can operate in the ISM frequency bands. However, time domain tags developed until now offer poor coding capacity. This thesis proposes a new method to increase the coding capacity of tags operating in time domain by using C-sections, i.e. the transmission lines are folded so as to have tightly coupled zones that give them a dispersive nature. Another approach based on a multi-layer technique was also introduced, in order to increase the coding capacity considerably. Finally, the proof of concept of a humidity sensor tag based on silicon nanowires is also presented.

Dans cette thèse, le concept d'identification par radiofréquence sans puce (chipless RFID) est étendu à l'authentification où chaque étiquette doit présenter une signature unique qui ne peut jamais être reproduite même si quelqu'un tente de copier l'étiquette. À cette fin, le caractère aléatoire naturel (c’est-à-dire inhérent au processus de fabrication) ainsi que les paramètres de dimension des résonateurs sont utilisés. Un tel caractère aléatoire naturel peut produire des signatures électromagnétiques (EM) uniques, éventuellement utilisées pour l'authentification. Initialement, nous avons prouvé l’idée proposée en appliquant intentionnellement les variations dimensionnelles le long des résonateurs. Différentes valeurs des variations dimensionnelles appliquées sont utilisées pour trouver la variation minimale détectable par l'approche radar sans puce RFID. De plus, une analyse statistique a été réalisée pour calculer les taux d'erreur. Par la suite, une approche par spectrogramme est proposée pour extraire des paramètres indépendants de l’aspect (c’est-à-dire la fréquence de résonance et le facteur de qualité) des étiquettes RFID sans puce. Enfin, nous avons fabriqué plusieurs résonateurs présentant un caractère aléatoire naturel (sans aucune variation dimensionnelle appliquée) afin de caractériser la performance des étiquettes sans puce pour les applications d'authentification. Des technologies de réalisation à faible coût basées sur des circuits imprimés avec un procédé de gravure chimique et l’impression à jet d’encre par une imprimante de bureau ordinaire sont utilisées. Le caractère aléatoire naturel selon les dimensions des résonateurs est également confirmé par l'analyse microscopique à l'aide d'un microscope numérique. / In this thesis, the concept of chipless radio frequency identification (RFID) is extended to the chipless authentication where each tag has to present a unique signature that can never be reproduced even if someone tries to copy the tag. For this purpose, natural randomness (i.e., inherent in the fabrication process) along dimension parameters of resonators is utilized. Such natural randomness can produce unique electromagnetic (EM) signatures that are possibly employed for authentication. Initially, we proved the proposed idea by purposely applying the dimensional variations along the resonators. Different values of the purposely applied dimensional variations are used to find the minimum detectable variation by the chipless RFID radar approach. Additionally, a statistical analysis has been performed to calculate the error rates. Subsequently, a spectrogram approach is proposed to extract aspect-independent parameters (i.e., the frequency of resonance and quality factor) of chipless RFID tags. Finally, we fabricated numerous resonators exhibiting natural randomness (without any purposely applied dimensional variations) to characterize the potential of the chipless tags for authentication applications. Low-cost realization technologies such as printed circuit board (PCB) using chemical etching process and inkjet printing using ordinary office printer are utilized. The natural randomness along the dimensions of resonators is also confirmed by the microscopic analysis using a digital microscope.

As prominent components of the Internet-of-Things (IoT) front-end, sensors capable of intelligently collecting sensing information from the surrounding environment with increasingly lower prices are required. Planar microwave chipless sensors could be a valid solution and will be the focus of this PhD research proposal. With a completely passive solution, that in its basic configuration is composed by only microstrip resonant structures and sensitive materials, this frequency-domain sensing technology results particularly adapt for the integration in smart devices. The objectives of the PhD activity will be to contribute with a further investigation of sensitive materials in the context of environmental monitoring and to test their reliability as sensitive components in controlled wired condition. The purpose is, then, to move from a wired controlled measurement to a wireless reading acquisition of the microwave sensing node response. Finally, the sensor potentialities will be further enriched by adopting fabrication techniques typical of the flexible electronics field. An inkjet printing strategy is investigated for the purpose trying to ensure good detection properties as in the case of standard fabricated tags.

Modern smartphone technology has created a myriad of opportunities in the field of RF and Microwave. Specifically, Chipless RFID sensor, compact microwave filter, antenna based on a microstrip structure, and many more. In this thesis, innovative ideas for the industrial and biomedical device has been explored. The work presents the reconfigurable filter design, Switch-beam antenna, Microwave interferometer, X-band Rotman Lens antenna, Ultra-wideband antenna based on SIW resonator, L-band Stepped Frequency Continuous Wave antenna, development of a wireless sensor system for environmental monitoring, Indoor Air Quality monitoring, and Wildfire Monitoring based on the modulated scattering technique (MST). The MST sensor probes are based on the scattering properties of small passive antennas and radiate part of the impinging electromagnetic field generated by an interrogating antenna, which also acquires the backscattered signal as information. The MST probes are able to deliver data without a radio frequency front end. They use a simple circuit that alternatively terminates the antenna probe on suitable loads to generate a low modulation signal on the backscattered electromagnetic wave. The antenna presented in this work has been designed in ADS Software by Keysight Technologies. The designed antenna has been assessed numerically and experimentally. The experimental measurement data demonstrate the effectiveness of the individual system. Simultaneously, the MST sensor system has been proposed to obtain the best performance in communication range, load efficiency, and power harvesting. The MST sensor has been fabricated and assessed in practical scenarios. The proposed prototype, able to provide a communication range of about 15 m, serves as a proof-of-concept. The acquired measurements of MST demonstrate the accuracy of the data without radio frequency front end or bulky wired connection with the same efficiency of standard wireless sensors such as radio frequency identifier (RFID) or wireless sensor networks (WSN).

Recently, Radio Frequency Identification (RFID) technology has become commonplace in many applications. It is based on storing and remotely retrieving the data embedded on the tags. The tag structure can be chipped or chipless. In chipped tags, an integrated IC attached to the antenna is biased by an onboard battery or interrogating signal. Compared to barcodes, the chipped tags are expensive because of the existence of the chip. That was why chipless RFID tags are demanded as a cheap candidate for chipped RFID tags and barcodes. As its name expresses, the geometry of the tag acts as both modulator and scatterer. As a modulator, it incorporates data into the received electric field launched from the reader antenna and reflects it back to the receiving antenna. The scattered signal from the tag is captured by the antenna and transferred to the reader for the detection process. By employing the singularity expansion method (SEM) and the characteristic mode theory (CMT), a systematic design process is introduced by which the resonant and radiation characteristics of the tag are monitored in the pole diagram versus structural parameters. The antenna is another component of the system. Taking advantage of ultra-wideband (UWB) technology, it is possible to study the time and frequency domain characteristics of the antenna used in chipless RFID system. A new omni-directional antenna element useful in wideband and UWB systems is presented. Then, a new time-frequency technique, called short-time matrix pencil method (STMPM), is introduced as an efficient approach for analyzing various scattering mechanisms in chipless RFID tags. By studying the performance of STMPM in early-time and late-time responses of the scatterers, the detection process is improved in cases of multiple tags located close to each other. A space-time-frequency algorithm is introduced based on STMPM to detect, identify, and localize multiple multi-bit chipless RFID tags in the reader area. The proposed technique has applications in electromagnetic and acoustic-based detection of targets. / Ph. D.

The objective of this work is to enhance and advance sensing technologies with the design and development of novel radio frequency (RF) sensors based on far-field and near-field principles of the electromagnetic (EM) resonances. In the first part of this thesis, original design and development of a passive RF temperature sensor, a passive RF strain sensor, and a passive RF pressure sensor are presented. The RF temperature sensor is presented in Chapter 3. It is based on split ring resonators loaded with bimorph cantilevers. Its operating principles and equivalent circuits are discussed in Chapter 4, where the design concept is illustrated to be robust and highly adaptable to different sensing ranges, environments, and applicable to other type of sensing beyond temperatures. The passive RF strain sensor, based on a patch antenna loaded with a cantilever-integrated open loop, is presented in Chapter 5, where it is demonstrated to have the highest strain sensitivity in the same remote and passive class of sensors in the state-of-the-art. Chapter 6 describes the passive RF pressure sensor, which is based on a dual-band stacked-patch antenna that allows both identification and sensing to be embedded in its unique dual resonant responses. In the second part of this thesis, an original and first-of-its-kind RF transducer is presented that enables non-touch sensing of human fingers within 3 cm of proximity (based on one unit sensor cell). The RF transducer is based on a slotted microstrip patch coupled to a half-wavelength parallel-coupled microstrip filter operating in the frequency range of 6 – 8 GHz. The sensing mechanism is based on the EM near-field coupling between the resonator and the human finger. Fundamentally different from the electric field capacitive sensing, this new method of sensing, the first of its kind, based on near-field interference that produces a myriad of nonlinearities in the sensing response, can introduce new capabilities for the interface of electronic displays (the detection is based on pattern recognition). What set this sensor and its platform apart from previous proximity sensors and microwave sensing platforms is the low profile planar structure of the system, and its compatibility with mobile applications. The thesis provides both breadth and depth in the proposed design and development and thus presenting a complete research in its contributions to RF sensing.

[pt] Estruturas baseadas em grafeno como óxido de grafeno (OG) e óxido de grafeno reduzido (OGr) vêm sendo amplamente utilizadas em aplicações de sensoriamento resistivo de gás. Entretanto, poucos projetos são efetuados utilizando métodos pervasivos e não intrusivos, que são importantes para aplicações onde intervenções podem ser problemáticas. Este trabalho apresenta a implementação de protótipos de sensores sem fio de baixo custo baseados na tecnologia de RFID sem chip, para sensoriamento de vapor de álcool, utilizando uma topologia de antena miniaturizada baseada em Metamateriais (MTMs) carregada com OGr. Simulações utilizando o método dos elementos finitos são efetuadas de forma a encontrar o melhor local para deposição das estruturas sensíveis ao vapor de álcool. É observado que a estrutura responde a variações de resistividade de OGr apenas para uma determinada faixa de valores. O tempo de redução térmica de OG necessário para atingir este espectro de valores é experimentalmente determinado, estando entre 60 e 90 min à 200 Graus Celsius. Amostras de GO são fabricadas utilizando o método de Hummer modificado, e são depositadas nos gaps das antenas. Posteriormente, são reduzidas por 60, 75 e 90 minutos. O setup de medição consistiu em medições do coeficiente de reflexão em banda X. Após um determinado tempo para estabilização, álcool isopropílico e também etanol são colocados em contato com a amostra em um recipiente fechado por 1h30, e a resposta foi observada. Resultados com sensibilidade de até 11,5 por cento foram obtidos. / [en] Graphene oxide (GO) and reduced graphene oxide (rGO) based structures have been widely applied for resistive gas sensing applications. However, few projects are developed using pervasive and non-intrusive methods, which are important for applications where intervention can be an issue. This work presents the implementation of low-cost wireless sensor prototypes based on chipless RFID technology, for alcohol vapor sensing, by using a metamaterial (MTM) based miniaturized antenna loaded with rGO. Simulations are performed using finite element method in order to find the best place to deposit the alcohol vapor sensitive structures. It is observed that the structure responds to resistivity variations only for a determined range of values. The GO reduction time necessary to reach this spectrum of values is experimentally determined, and it is found to be between 60 and 90 min at 200 Celsius degrees. GO samples are synthesized using a modified Hummer s method, and deposited in the gaps of the antenna structures. Later, they are reduced for 60, 75 and 90 min. The measurement setup consists in reflection coefficient characterization at X band frequencies. After a stabilization time, isopropyl alcohol and ethanol are put in contact with the samples in a closed container for 1h30, and the response is observed. Sensitivities up to 11,5 percent are obtained.