In this thesis, we have designed and optimized strip waveguide based micro-ring and micro-ring and micro-racetrack resonators for biosensing applications. Silicon-On-Insulator (SOI) platform which offers several advantages over other materials such as Lithium Niobate, Silica on Silicon and Silicon nitride is considered here. High index contrast enables us to miniaturize the biosensor devices and monolithic integration of source and detectors on the same chip. We have considered the dispersive nature of the waveguide and proceeded towards optimization. Finite difference schemes and Finite Difference Time Domain (FDTD) methods are the primary tools used to model the biosensor. Various structures such as channel waveguides and beam structures are analyzed on the basis of their suitability for sensing applications. Strip and Rib waveguides are the two geometries considered in our studies. In an optical guiding structure, effective index of the propagating optical mode can be induced by two different phenomena: i. Homogeneous Sensing In this category, effective index of a propagating optical mode changes with uniformly distributed analytes extending over a distance well exceeding the evanescent field penetration depth. The sample serves as the waveguide cover. ii. Surface Sensing In the case of surface sensing, analytes bound to the surface of the waveguide. The effective index of an optical mode changes with the refractive index as well as the thickness of an adlayer. A thin layer of adsorbed or bound molecules transported from liquid or gaseous medium serving as waveguide cover is referred as an adlayer. Both homogeneous and surface sensing schemes are addresses in this work. By bulk sensing method, the characteristics of bioclad covering the device are studied. Optimization of the resonator structure involves the analysis of following parameters: • Gap between the ring and bus waveguides • Free spectral range • Extinction ratio • Quality factor We have achieved a maximum bulk sensitivity of 115 nm / RIU with ring waveguide width of 450 nm and bus width of 350 nm which is better than an earlier reported value of 70 nm/ RIU. We have proposed a novel detection scheme consisting of a micro-racetrack resonator formed over a cantilever structure. The devoice works on the principle of opto-mechanical coupling to detect conformational changes due to biomolecular adherence. BSA (Bovine Serum Albumin) and IgG ( Immuno Globulin G) are the two proteins considered in the work. Mechanical analysis of the beam for tensile and compressive stresses and corresponding spectral responses of the racetrack resonators are analyzed both by semi-analytical and method and numerical analyzes. We compared various aspects of rib and strip waveguide racetrack resonators. We have proved by numerical simulation, that the device is capable of distinguishing tensile and compressive stress. Two strip waveguides of dimensions : 450 nm X 220 nm and 400 nm X 180 nm, former supporting both Quasi-TE and Quasi-TM modes where as the second configuration allows only Quasi-TE mode alone. Sensitivity of the cantilever sensor is : 0.3196 x 10-3 nm/ µɛ at 1550 nm wavelength.

Cette thèse traite des équations de Maxwell en domaine temporel. Le principal objectif est de proposer des méthodes de type éléments finis d'ordre élevé pour les équations de Maxwell et des schémas d'intégration en temps efficaces sur des maillages localement raffinés. Nous considérons des méthodes GDDT (Galerkine Discontinues en Domaine Temporel) s'appuyant sur une interpolation polynomiale d'ordre arbitrairement élevé des composantes du champ électromagnétique. Les méthodes GDDT pour les équations de Maxwell s'appuient le plus souvent sur des schémas d'intégration en temps explicites dont la condition de stabilité peut être très restrictive pour des maillages raffinés. Pour surmonter cette limitation, nous considérons des schémas en temps qui consistent à appliquer un schéma implicite localement, dans les régions raffinées, tout en préservant un schéma explicite sur le reste du maillage. Nous présentons une étude théorique complète et une comparaison de deux méthodes GDDT localement implicites. Des expériences numériques en 2D et 3D illustrent l'utilité des schémas proposés. Le traitement numérique de milieux de propagation complexes est également l'un des objectifs. Nous considérons l'interaction des ondes électromagnétiques avec les tissus biologiques qui est au cœur de nombreuses applications dans le domaine biomédical. La modélisation numérique nécessite alors de résoudre le système de Maxwell avec des modèles appropriés de dispersion. Nous formulons une méthode GDDT localement implicite pour le modèle de Debye et proposons une analyse théorique et numérique complète du schéma. / This work deals with the time-domain formulation of Maxwell's equations. The main objective is to propose high-order finite element type methods for the discretization of Maxwell's equations and efficient time integration methods on locally refined meshes. We consider Discontinuous Galerkin Time-Domain (DGTD) methods relying on an arbitrary high-order polynomial interpolation of the components of the electromagnetic field. Existing DGTD methods for Maxwell's equations often rely on explicit time integration schemes and are constrained by a stability condition that can be very restrictive on highly refined meshes. To overcome this limitation, we consider time integration schemes that consist in applying an implicit scheme locally i.e. in the refined regions of the mesh, while preserving an explicit scheme in the complementary part. We present a full theoretical study and a comparison of two locally implicit DGTD methods. Numerical experiments for 2D and 3D problems illustrate the usefulness of the proposed time integration schemes. The numerical treatment of complex propagation media is also one of the objectives. We consider the interaction of electromagnetic waves with biological tissues that is of interest to applications in biomedical domain. Numerical modeling then requires to solve the system of Maxwell's equations coupled to appropriate models of physical dispersion. We derive a locally implicit DGTD method for the Debye model and we achieve a full theoretical and numerical analysis of the resulting scheme.

Diplomová práce se zabývá metodou hybridních (hranových a uzlových) konečných prvků ve frekvenční i časové oblasti. Tato metoda je použita pro analýzu vlnovodu parallel-plate, v kterém jsou umístěny dvě dielektrické vrstvy. Jako ukončení vlnovodu je implementována dokonale přizpůsobená vrstva označována PML. Projekt řeší možný výběr PML vrstvy v časové oblasti. Metoda je programována v programu MATLAB a výsledky jsou porovnány s programem COMSOL Multiphysics.

<p>Дисертација истражује најприхватљивије методе мерења стабилности фреквенције у<br />фреквенцијском домену, односно мерење вредности величине &bdquo;фазни шум&ldquo;, приликом<br />процеса еталонирања мерне опреме. Када се говори о мерној опреми која је предмет<br />еталонирања, дисертација је, пре свега, окренута ка еталонирању врхунских<br />комерцијалних стандарда (еталона) фреквенције. Приказана истраживања су била основ<br />за покретање и реализацију истраживачко-развојног пројекта у оквиру Министарства<br />одбране, који је имао за циљ оспособљавање метролошке лабораторије Техничког<br />опитног центра Војске Србије за потпуно еталонирање мерне опреме из области<br />времена и фреквенције. Различите методе мерења подразумевају и различите мерне<br />могућности, као и врло широк спектар еталонске и мерне опреме која се користи при<br />њиховој реализацији. У дисертацији се приказују различити начини мерења фазног шума<br />и описују методе реализоване на основу доступне мерне опреме. Како се ради о<br />методама упоредне анализе референтног и мереног сигнала, посебно критична позиција<br />је одабир референце, односно референтног еталона. Истраживање је довело до<br />закључака којима је предложен метод мерења потребне и довољне мерне несигурности<br />као и начин реализације изабране методе, односно одабир еталонске мерне опреме. У<br />циљу увођења мерне методе у употребу, извршена су и приказана мерења на<br />различитим типовима и врстама мерне опреме. Валидација методе је остварена<br />билатералним поређењем са Дирекцијом за мере и драгоцене метале, Група за време,<br />фреквенцију и дистрибуцију времена. Да је могуће реализовати методу мерења фазног<br />шума приликом еталонирања најквалитетнијих осцилатора је постављена хипотеза<br />дисертације, која је истраживањем доказана и практично спроведена. Крајњи резултат<br />истраживања је довео до увођења признате методе еталонирања фазног шума, први пут</p> / <p>Disertacija istražuje najprihvatljivije metode merenja stabilnosti frekvencije u<br />frekvencijskom domenu, odnosno merenje vrednosti veličine &bdquo;fazni šum&ldquo;, prilikom<br />procesa etaloniranja merne opreme. Kada se govori o mernoj opremi koja je predmet<br />etaloniranja, disertacija je, pre svega, okrenuta ka etaloniranju vrhunskih<br />komercijalnih standarda (etalona) frekvencije. Prikazana istraživanja su bila osnov<br />za pokretanje i realizaciju istraživačko-razvojnog projekta u okviru Ministarstva<br />odbrane, koji je imao za cilj osposobljavanje metrološke laboratorije Tehničkog<br />opitnog centra Vojske Srbije za potpuno etaloniranje merne opreme iz oblasti<br />vremena i frekvencije. Različite metode merenja podrazumevaju i različite merne<br />mogućnosti, kao i vrlo širok spektar etalonske i merne opreme koja se koristi pri<br />njihovoj realizaciji. U disertaciji se prikazuju različiti načini merenja faznog šuma<br />i opisuju metode realizovane na osnovu dostupne merne opreme. Kako se radi o<br />metodama uporedne analize referentnog i merenog signala, posebno kritična pozicija<br />je odabir reference, odnosno referentnog etalona. Istraživanje je dovelo do<br />zaključaka kojima je predložen metod merenja potrebne i dovoljne merne nesigurnosti<br />kao i način realizacije izabrane metode, odnosno odabir etalonske merne opreme. U<br />cilju uvođenja merne metode u upotrebu, izvršena su i prikazana merenja na<br />različitim tipovima i vrstama merne opreme. Validacija metode je ostvarena<br />bilateralnim poređenjem sa Direkcijom za mere i dragocene metale, Grupa za vreme,<br />frekvenciju i distribuciju vremena. Da je moguće realizovati metodu merenja faznog<br />šuma prilikom etaloniranja najkvalitetnijih oscilatora je postavljena hipoteza<br />disertacije, koja je istraživanjem dokazana i praktično sprovedena. Krajnji rezultat<br />istraživanja je doveo do uvođenja priznate metode etaloniranja faznog šuma, prvi put</p> / <p>The dissertation examines the most acceptable methods for measuring the frequency stability<br />in the frequency domain, that is, measuring the value of the &quot;phase noise&quot;, during the process<br />of measuring equipment calibration. When it comes to measuring equipment as a subject of<br />calibration, the dissertation is, first of all, oriented towards the calibration of the highest<br />commercial frequency standards. The presented researches were the basis for initiation and<br />realization of the research and development project within the Ministry of Defense, which was<br />aimed at training the metrology laboratory of the Technical Test Center of the Serbian Army<br />for complete calibration of measuring equipment in the area of time and frequency. Different<br />measurement methods also involve different measurement possibilities, as well as a very wide<br />range of calibration and measuring equipment used in their realization. Different methods of<br />measuring phase noise are described in the dissertation and they describe realized methods<br />based on available measuring equipment. As for methods of comparative analysis of the<br />reference and measured signal, a particularly critical position is the selection of the reference,<br />that is, the reference oscillator. The research led to conclusions suggesting the method of<br />measuring the necessary and sufficient measurement uncertainty, as well as the method of<br />realization of the chosen method, i.e. selection of the standard measuring equipment. In order<br />to put the measurement method into practice, measurements were performed on different<br />types of measuring equipment. Validation of the method was achieved by bilateral<br />comparison with the Directorate of Measures and Precious Metals, Group for time, frequency<br />and time dissemination. The possibility to realize the method of phase noise measurement<br />during the calibration of the highest quality oscillators is a hypothesis of the dissertation that<br />has been set up, and has been proven and practically carried out by the research. The final<br />result of the research led to the introduction of a recognized calibration method of the phase<br />noise, for the first time in the Republic of Serbia.</p>

This work addresses the question of the efficient numerical solution of time-domain boundary integral equations with retarded potentials arising in the problems of acoustic and electromagnetic scattering. The convolutional form of the time-domain boundary operators allows to discretize them with the help of Runge-Kutta convolution quadrature. This method combines Laplace-transform and time-stepping approaches and requires the explicit form of the fundamental solution only in the Laplace domain to be known. Recent numerical and analytical studies revealed excellent properties of Runge-Kutta convolution quadrature, e.g. high convergence order, stability, low dissipation and dispersion. As a model problem, we consider the wave scattering in three dimensions. The convolution quadrature discretization of the indirect formulation for the three-dimensional wave equation leads to the lower triangular Toeplitz system of equations. Each entry of this system is a boundary integral operator with a kernel defined by convolution quadrature. In this work we develop an efficient method of almost linear complexity for the solution of this system based on the existing recursive algorithm. The latter requires the construction of many discretizations of the Helmholtz boundary single layer operator for a wide range of complex wavenumbers. This leads to two main problems: the need to construct many dense matrices and to evaluate many singular and near-singular integrals. The first problem is overcome by the use of data-sparse techniques, namely, the high-frequency fast multipole method (HF FMM) and H-matrices. The applicability of both techniques for the discretization of the Helmholtz boundary single-layer operators with complex wavenumbers is analyzed. It is shown that the presence of decay can favorably affect the length of the fast multipole expansions and thus reduce the matrix-vector multiplication times. The performance of H-matrices and the HF FMM is compared for a range of complex wavenumbers, and the strategy to choose between two techniques is suggested. The second problem, namely, the assembly of many singular and nearly-singular integrals, is solved by the use of the Huygens principle. In this work we prove that kernels of the boundary integral operators $w_n^h(d)$ ($h$ is the time step and $t_n=nh$ is the time) exhibit exponential decay outside of the neighborhood of $d=nh$ (this is the consequence of the Huygens principle). The size of the support of these kernels for fixed $h$ increases with $n$ as $n^a,a<1$, where $a$ depends on the order of the Runge-Kutta method and is (typically) smaller for Runge-Kutta methods of higher order. Numerical experiments demonstrate that theoretically predicted values of $a$ are quite close to optimal. In the work it is shown how this property can be used in the recursive algorithm to construct only a few matrices with the near-field, while for the rest of the matrices the far-field only is assembled. The resulting method allows to solve the three-dimensional wave scattering problem with asymptotically almost linear complexity. The efficiency of the approach is confirmed by extensive numerical experiments.

[EN] Fiber grating sensors and devices have demonstrated outstanding capabilities in both telecommunications and sensing areas, due to their well-known advantageous characteristics. Therefore, one of the most important motivations lies in the potential of customized fiber gratings to be suitably employed for improving the interrogation process of optical fiber sensors and systems. This Ph.D. dissertation is focused on the study, design, fabrication and performance evaluation of customized fiber Bragg gratings (FBGs) and long period gratings (LPGs) with the double aim to present novel sensing technologies and to enhance the response of existing sensing systems. In this context, a technique based on time-frequency domain analysis has been studied and applied to interrogate different kind of FBGs-based sensors. The distribution of the central wavelength along the sensing structures has been demonstrated, based on a combination of frequency scanning of the interrogating optical pulse and optical time-domain reflectometry (OTDR), allowing the detection of spot events with good performance in terms of measurand resolution. Moreover, different customized FBGs have been interrogated using a technology inspired on the operation principle of microwave photonics (MWP) filters, enabling the detection of spot events using radio-frequency (RF) devices with modest bandwidth. The sensing capability of these technological platforms has been fruitfully employed for implementing a large scale quasi-distributed sensor, based on an array of cascaded FBGs. The potentiality of LPGs as fiber optic sensors has also been investigated in a new fashion, exploiting the potentials of MWP filtering techniques. Besides, a novel approach for simultaneous measurements based on a half-coated LPG has been proposed and demonstrated. Finally, the feasibility of FBGs as selective wavelength filters has been exploited in sensing applications; an alternative approach to improve the response and performance of Brillouin distributed fiber sensors has been studied and validated via experiments. The performance of the reported sensing platforms have been analyzed and evaluated so as to characterize their impact on the fiber sensing field and to ultimately identify the use of the most suitable technology depending on the processing task to be carried out and on the final goal to reach. / [ES] Los sensores y dispositivos en fibra basados en redes de difracción han mostrado excepcionales capacidades en el ámbito de las telecomunicaciones y del sensado, gracias a sus excelentes propiedades. Entre las motivaciones más estimulantes destaca la posibilidad de fabricar redes de difracción ad-hoc para implementar y/o mejorar las prestaciones de los sensores fotónicos. Esta tesis doctoral se ha enfocado en el estudio, diseño, fabricación y evaluación de las prestaciones de redes de difracción de Bragg (FBGs) y de redes de difracción de periodo largo (LPGs) personalizadas con el fin de desarrollar nuevas plataformas de detección y a la vez mejorar la respuesta y las prestaciones de los sensores fotónicos ya existentes. En este contexto, una técnica basada en el análisis tiempofrecuencia se ha estudiado e implementado para la interrogación de sensores en fibra basados en varios tipos y modelos de FBGs. Se ha analizado la distribución de la longitud de onda central a lo largo de la estructura de sensado, gracias a una metodología que conlleva el escaneo en frecuencia del pulso óptico incidente y la técnica conocida como reflectometria óptica en el dominio del tiempo (OTDR). De esta manera se ha llevado a cabo la detección de eventos puntuales, alcanzando muy buenas prestaciones en términos de resolución de la magnitud a medir. Además, se han interrogado varias FBGs a través de una técnica basada en el principio de operación de los filtros de fotónica de microondas (MWP), logrando así la detección de eventos puntuales usando dispositivos de radio-frecuencia (RF) caracterizados por un moderado ancho de banda. La capacidad de sensado de estas plataformas tecnológicas ha sido aprovechada para la realización de un sensor quasi-distribuido de gran alcance, formado por una estructura en cascada de muchas FBGs. Por otro lado, se han puesto a prueba las capacidades de las LPGs como sensores ópticos según un enfoque novedoso; para ello se han aprovechados las potencialidades de los filtros de MWP. Asimismo, se ha estudiado y demostrado un nuevo método para medidas simultáneas de dos parámetros, basado en una LPG parcialmente recubierta por una película polimérica. Finalmente, se ha explotado la viabilidad de las FBGs en cuanto al filtrado selectivo en longitud de onda para aplicaciones de sensado; para ello se ha propuesto un sistema alternativo para la mejora de la respuesta y de las prestaciones de sensores ópticos distribuidos basados en el scattering de Brillouin. En conclusión, se han analizado y evaluado las prestaciones de las plataformas de sensado propuestas para caracterizar su impacto en el ámbito de los sistemas de detección por fibra y además identificar el uso de la tecnología más adecuada dependiendo de la tarea a desarrollar y del objetivo a alcanzar. / [CA] Els sensors i dispositius en fibra basats en xarxes de difracció han mostrat excepcionals capacitats en l'àmbit de les telecomunicacions i del sensat, gràcies a les seus excel¿lents propietats. Entre les motivacions més estimulants destaca la possibilitat de fabricar xarxes de difracció ad-hoc per a implementar i/o millorar les prestacions de sensors fotònics. Esta tesi doctoral s'ha enfocat en l'estudi, disseny, fabricació i avaluació de les prestacions de xarxes de difracció de Bragg (FBGs) i de xarxes de difracció de període llarg (LPGs) personalitzades per tal de desenvolupar noves plataformes de detecció i al mateix temps millorar la resposta i les prestacions dels sensors fotònics ja existents. En este context, una tècnica basada en l'anàlisi temps-freqüència s'ha estudiat i implementat per a la interrogació de sensors en fibra basats en diversos tipus i models de FBGs. S'ha analitzat la distribució de la longitud d'ona central al llarg de l'estructura de sensat, gràcies a una metodologia que comporta l'escaneig en freqüència del pols òptic incident i la tècnica coneguda com reflectometria òptica en el domini del temps (OTDR). D'esta manera s'ha dut a terme la detecció d'esdeveniments puntuals, aconseguint molt bones prestacions en termes de resolució de la magnitud a mesurar. A més, s'han interrogat diverses FBGs a través d'una tècnica basada en el principi d'operació dels filtres de fotònica de microones (MWP), aconseguint així la detecció d'esdeveniments puntuals utilitzant dispositius de ràdio-freqüència (RF) caracteritzats per un moderat ample de banda. La capacitat de sensat d'aquestes plataformes tecnològiques ha sigut aprofitada per a la realització d'un sensor quasi-distribuït a llarga escala, format per una estructura en cascada de moltes FBGs. D'altra banda, s'han posat a prova les capacitats de les LPGs com a sensors òptics segons un enfocament nou; per a això s'han aprofitat les potencialitats dels filtres de MWP. Així mateix, s'ha estudiat i demostrat un nou mètode per a mesures simultànies de dos paràmetres, basat en una LPG parcialment recoberta per una pel¿lícula polimèrica. Finalment, s'ha explotat la viabilitat de les FBGs pel que fa al filtrat selectiu en longitud d'ona per a aplicacions de sensat; per això s'ha proposat un sistema alternatiu per a la millora de la resposta i de les prestacions de sensors òptics distribuïts basats en el scattering de Brillouin. S'han analitzat i avaluat les prestacions de les plataformes de sensat propostes per a caracteritzar el seu impacte en l'àmbit dels sistemes de detecció per fibra i a més identificar l'ús de la tecnologia més adequada depenent de la tasca a desenvolupar i de l'objectiu a assolir. / Ricchiuti, AL. (2016). Design and fabrication of customized fiber gratings to improve the interrogation of optical fiber sensors [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/66343 / TESIS / Premios Extraordinarios de tesis doctorales

In dieser Arbeit untersuchen wir das optische Antwortverhalten von planaren Spektrometern basierend auf ungeordneten Streuzentren, dielektrischen Verbundnanopartikeln mit einer plasmonischer Ummantelung, sowie volldielektrischen magnetooptischen formveränderten Metaoberflächen. Dafür benutzen wir sowohl Mie und Mehrfach-Streutheorie als auch ein unstetiges Galerkin Zeitraumverfahren basierend auf finiten Elementen zur numerischen Berechnung der elektromagnetischen Felder. Wir stellen insbesondere eine theoretische Designstudie vor, um ungeordnete Spektrometer mit hoher spektraler Auflösung zu erhalten. Darüber hinaus geben wir eine alternative Strategie an, um durch Untersuchung der optischen Eigenschaften von Verbundnanopartikeln eine Erhöhung der bevorzugten Rückstreuung zu erreichen. Zum Schluss präsentieren wir eine Erhöhung der Faraday-Rotation bei gleichzeitig hoher Transmission von volldielektrischen magnetooptischen Metaoberflächen, welche aus formangepassten Nanodisks bestehen. / In this thesis, we study the optical response of planar spectrometers based on disorder scatterers, composite dielectric nanoparticles with plasmonic shell, and all-dielectric magneto-optical shape-modified metasurfaces. Therefore, we employ both Mie and multiple scattering theory as well as a discontinuous Galerkin time-domain method based on finite elements for the numerical computation of the electromagnetic fields. Specifically, we present a theoretical design study for obtaining random spectrometers with high spectral resolution. Furthermore, we provide an alternative strategy to achieve preferentially high backscattering by studying the optical properties of composite nanoparticles. Finally, we present enhanced Faraday rotation along with high transmittance in all-dielectric magneto-optical metasurfaces composed of shape-modified nanodisks.

Network reconstruction is the process of recovering a unique structured representation of some dynamic system using input-output data and some additional knowledge about the structure of the system. Many network reconstruction algorithms have been proposed in recent years, most dealing with the reconstruction of strictly proper networks (i.e., networks that require delays in all dynamics between measured variables). However, no reconstruction technique presently exists capable of recovering both the structure and dynamics of networks where links are proper (delays in dynamics are not required) and not necessarily strictly proper.The ultimate objective of this dissertation is to develop algorithms capable of reconstructing proper networks, and this objective will be addressed in three parts. The first part lays the foundation for the theory of mathematical representations of proper networks, including an exposition on when such networks are well-posed (i.e., physically realizable). The second part studies the notions of abstractions of a network, which are other networks that preserve certain properties of the original network but contain less structural information. As such, abstractions require less a priori information to reconstruct from data than the original network, which allows previously-unsolvable problems to become solvable. The third part addresses our original objective and presents reconstruction algorithms to recover proper networks in both the time domain and in the frequency domain.

The emergence of Ultra-wideband (UWB) technology application has yielded tremendous and vital impacts in the field of microwave wireless communications. These applications include military radar imaging, security screening, and tumour detection, especially for early detection of breast cancer. These indicators have stimulated and inspired many researchers to make the best use of this promising technology. UWB technology challenges such as antenna design, the problem of imaging reconstruction techniques, challenges of severe signal attenuation and dispersion in high loss material. Others are lengthy computational time demand and large computer memory requirements are prevalent constraints that need to be tackled especially in a large scale and complex computational electromagnetic analysis. In this regard, it is necessary to find out recently developed optimisation techniques that can provide solutions to these problems. In this thesis, designing, optimisation, development, measurement, and analysis of UWB antennas for near-field microwave imaging applications are considered. This technology emulates the same concept of surface penetrating radar operating in various forms of the UWB spectrum. The initial design of UWB monopole antennas, including T-slots, rectangular slots, and hexagonal slots on a circular radiating patch, was explicitly implemented for medical imaging applications to cover the UWB frequency ranging from 3.1 GHz to 10.6 GHz. Based on this concept, a new bow-tie and Vivaldi UWB antennas were designed for a through-the-wall imaging application. The new antennas were designed to cover a spectrum on a lower frequency ranging from 1 GHz - 4 GHz to ease the high wall losses that will be encountered when using a higher frequency range and to guarantee deeper penetration of the electromagnetic wave. Finally, both simulated and calculated results of the designed, optimised antennas indicate excellent agreement with improved performance in terms of return loss, gain, radiation pattern, and fidelity over the entire UWB frequency. These breakthroughs provided reduced computational time and computer memory requirement for useful, efficient, reliable, and compact sensors for imaging applications, including security and breast cancer detection, thereby saving more lives. / Tertiary Education Trust Fund (TET Fund) Supported by the Nigerian Defence Academy (NDA)

<p>The last few decades have witnessed unprecedented growth in multiple areas of electronics spanning low-power sensing, intelligent computing and high-speed wireless connectivity. In the foreseeable future, there would be hundreds of billions of computing devices, sensors, things and people, wherein the technology will become intertwined with our lives through continuous interaction and collaboration between humans and machines. Such human-centric ideas give rise to the concept of internet of bodies (IoB), which calls for novel and energy-efficient techniques for sensing, processing and secure communication for resource-constrained IoB nodes.As we have painfully learnt during the pandemic, point-of-care diagnostics along with continuous sensing and long-term connectivity has become one of the major requirements in the healthcare industry, further emphasizing the need for energy-efficiency and security in the resource-constrained devices around us.</p> <p>  </p> <p>  With this vision in mind, I’ll divide this dissertation into the following chapters. The first part (Chapter 2) will cover time-domain sensing techniques which allow inherent energy-resolution scalability, and will show the fundamental limits of achievable resolution. Implementations will include 1) a radiation sensing system for occupational dosimetry in healthcare and mining applications, which can achieve 12-18 bit resolution with 0.01-1 µJ energy dissipation, and 2) an ADC-less neural signal acquisition system with direct Analog to Time Conversion at 13pJ/Sample. The second part (Chapters 3 and 4) of this dissertation will involve the fundamentals of developing secure energy-efficient electro-quasistatic (EQS) communication techniques for IoB wearables as well as implants, and will demonstrate  2 examples: 1) Adiabatic Switching for breaking the αCV^2f limit of power consumption in capacitive voltage mode human-body communication (HBC), and 2) Bi-Phasic Quasistatic Brain Communication (BP-QBC) for fully wireless data transfer from a sub-6mm^3, 2 µW brain implant. A custom modulation scheme, along with adiabatic communication enables wireline-like energy efficiencies (<5pJ/b) in HBC-based wireless systems, while the BP-QBC node, being fully electrical in nature, demonstrates sub-50pJ/b efficiencies by eliminating DC power consumption, and by avoiding the transduction losses observed in competing technologies, involving optical, ultrasound and magneto-electric modalities. Next in Chapter 5, we will show an implementation of a reconfigurable system that would include 1) a human-body communication transceiver and 2) a traditional wireless (MedRadio) transceiver on the same integrated circuit (IC), and would demonstrate methods to switch between the two modes by detecting the placement of the transmitter and receiver devices (on-body/away from the body). Finally, in Chapter 6, we shall show a technique of augmenting security in resource-constrained devices through authentication using the Analog/RF properties of the transmitter, which are usually discarded as non-idealities in a digital transceiver chain. This method does not require any additional hardware in the transmitter, making it an extremely promising technique to augment security in highly resource-constrained scenarios. Such energy-efficient intelligent sensing and secure communication techniques, when combined with intelligent in-sensor-analytics at the resource-constrained nodes, can potentially pave the way for perpetual, and even batteryless systems for next-generation IoT, IoB and healthcare applications.</p>