L’attività di ricerca contenuta in questa tesi si è concentrata nello sviluppo e nell’implementazione di tecniche per la co-simulazione e il co-progetto non lineare/elettromagnetico di sistemi wireless non convenzionali. Questo lavoro presenta un metodo rigoroso per considerare le interazioni tra due sistemi posti sia in condizioni di campo vicino che in condizioni di campo lontano. In sostanza, gli effetti del sistema trasmittente sono rappresentati da un generatore equivalente di Norton posto in parallelo all’antenna del sistema ricevente, calcolato per mezzo del teorema di reciprocità e del teorema di equivalenza. La correttezza del metodo è stata verificata per mezzo di simulazioni e misure, concordi tra loro. La stessa teoria, ampliata con l’introduzione degli effetti di scattering, è stata usata per valutare una condizione analoga, dove l’elemento trasmittente coincide con quello ricevente (DIE) contenuto all’interno di una struttura metallica (package). I risultati sono stati confrontati con i medesimi ottenibili tramite tecniche FEM e FDTD/FIT, che richiedono tempi di simulazione maggiori di un ordine di grandezza. Grazie ai metodi di co-simulazione non lineari/EM sopra esposti, è stato progettato e verificato un sistema di localizzazione e identificazione di oggetti taggati posti in ambiente indoor. Questo è stato ottenuto dotando il sistema di lettura, denominato RID (Remotely Identify and Detect), di funzioni di scansione angolare e della tecnica di RADAR mono-pulse. Il sistema sperimentale, creato con dispositivi low cost, opera a 2.5 GHz ed ha le dimensioni paragonabili ad un normale PDA. E’ stato sperimentata la capacità del RID di localizzare, in scenari indoor, oggetti statici e in movimento. / The research that has been conducted during the three years of the PhD graduation was focused on the development and the practical implementation of nonlinear/EM techniques of co-simulation and projecting of wireless systems. This work introduces a rigorous methodology for predicting the interaction between two systems in the near- and far-field situations. The results of a full-wave EM simulation of the harvesting antenna are rigorously handled by EM theory to produce a Norton equivalent circuit of the antenna in the presence of an incident field. In turn, this allows a full nonlinear analysis of any circuit connected to the antenna. The computed and measured performance of a pair of patch antennas compare very favorably in different real-world scenarios including near- and far-field situations. The same theory can be applied to a similar situation where the harvesting and transmitting antennas are the same circuit, enclosed into a metal package. The metal enclosure is treated as a scatterer that radiates back the incident field generated by the unpackaged circuit, and the effects of such scattered field on circuit performance are evaluated by the reciprocity theorem. The results compare favorably with those produced by FEM and FDTD/FIT methods. Thanks to these same nonlinear/EM techniques of co-simulation, a new long-distance microwave reading system has been projected, that we shall call RID (Remotely Identify and Detect), able to locate and identify objects in harsh indoor environments. This is obtained by augmenting standard RFID reader operations with the mono-pulse RADAR principle and electronic beam scanning capabilities. The technique is experimented at 2.45 GHz. This results in an handheld low cost device with total dimensions comparable with typical PDAs. The system capabilities are demonstrated in indoor scenarios locating and selecting closely-spaced tagged items, fixed or moving.

This thesis proposes design methods and test tools, for optical systems, which may be used in an industrial environment, where not only precision and reliability but also ease of use is important. The approach to the problem has been conceived to be as general as possible, although in the present work, the design of a portable device for automatic identification applications has been studied, because this doctorate has been funded by Datalogic Scanning Group s.r.l., a world-class producer of barcode readers. The main functional components of the complete device are: electro-optical imaging, illumination and pattern generator systems. For what concerns the electro-optical imaging system, a characterization tool and an analysis one has been developed to check if the desired performance of the system has been achieved. Moreover, two design tools for optimizing the imaging system have been implemented. The first optimizes just the core of the system, the optical part, improving its performance ignoring all other contributions and generating a good starting point for the optimization of the whole complex system. The second tool optimizes the system taking into account its behavior with a model as near as possible to reality including optics, electronics and detection. For what concerns the illumination and the pattern generator systems, two tools have been implemented. The first allows the design of free-form lenses described by an arbitrary analytical function exited by an incoherent source and is able to provide custom illumination conditions for all kind of applications. The second tool consists of a new method to design Diffractive Optical Elements excited by a coherent source for large pattern angles using the Iterative Fourier Transform Algorithm. Validation of the design tools has been obtained, whenever possible, comparing the performance of the designed systems with those of fabricated prototypes. In other cases simulations have been used.

The present PhD thesis exploits the design skills I have been improving since my master thesis’ research. A brief description of the chapters’ content follows. Chapter 1: the simulation of a complete front–end is a very complex problem and, in particular, is the basis upon which the prediction of the overall performance of the system is possible. By means of a commercial EM simulation tool and a rigorous nonlinear/EM circuit co–simulation based on the Reciprocity Theorem, the above–mentioned prediction can be achieved and exploited for wireless links characterization. This will represent the theoretical basics of the entire present thesis and will be supported by two RF applications. Chapter 2: an extensive dissertation about Magneto–Dielectric (MD) materials will be presented, together with their peculiar characteristics as substrates for antenna miniaturization purposes. A designed and tested device for RF on–body applications will be described in detail. Finally, future research will be discussed. Chapter 3: this chapter will deal with the issue regarding the exploitation of renewable energy sources for low–energy consumption devices. Hence the problem related to the so–called energy harvesting will be tackled and a first attempt to deploy THz solar energy in an innovative way will be presented and discussed. Future research will be proposed as well. Chapter 4: graphene is a very promising material for devices to be exploited in the RF and THz frequency range for a wide range of engineering applications, including those ones marked as the main research goal of the present thesis. This chapter will present the results obtained during my research period at the National Institute for Research and Development in Microtechnologies (IMT) in Bucharest, Romania. It will concern the design and manufacturing of antennas and diodes made in graphene–based technology for detection/rectification purposes.

This dissertation deals with the design and the characterization of novel reconfigurable silicon-on-insulator (SOI) devices to filter and route optical signals on-chip. Design is carried out through circuit simulations based on basic circuit elements (Building Blocks, BBs) in order to prove the feasibility of an approach allowing to move the design of Photonic Integrated Circuits (PICs) toward the system level. CMOS compatibility and large integration scale make SOI one of the most promising material to realize PICs. The concepts of generic foundry and BB based circuit simulations for the design are emerging as a solution to reduce the costs and increase the circuit complexity. To validate the BB based approach, the development of some of the most important BBs is performed first. A novel tunable coupler is also presented and it is demonstrated to be a valuable alternative to the known solutions. Two novel multi-element PICs are then analysed: a narrow linewidth single mode resonator and a passband filter with widely tunable bandwidth. Extensive circuit simulations are carried out to determine their performance, taking into account fabrication tolerances. The first PIC is based on two Grating Assisted Couplers in a ring resonator (RR) configuration. It is shown that a trade-off between performance, resonance bandwidth and device footprint has to be performed. The device could be employed to realize reconfigurable add-drop de/multiplexers. Sensitivity with respect to fabrication tolerances and spurious effects is however observed. The second PIC is based on an unbalanced Mach-Zehnder interferometer loaded with two RRs. Overall good performance and robustness to fabrication tolerances and nonlinear effects have confirmed its applicability for the realization of flexible optical systems. Simulated and measured devices behaviour is shown to be in agreement thus demonstrating the viability of a BB based approach to the design of complex PICs.

In the framework of the synthesis of time-modulated array antennas for communication purposes, the thesis focuses on the analysis and the development of innovative approaches aimed at reducing the power losses related with the undesired harmonic radiations. The accurate analysis of the problem in hand has been used to identify the fundamental parameters involved in the waste of power when the elements of the array are modulated using RF switches. The sideband radiations have been firstly indirectly handled throughout the reduction of the sideband levels of the patterns of the harmonics by means of the minimization of a suitable cost function using a stochastic optimizer, the Particle Swarm Optimizer. Successively, by exploiting a closed form relationship describing the total power wasted in sideband radiations a new synthesis method has been developed allowing a significant reduction of the computation effort and a more effective dealing with the synthesis problem. Moreover, a careful study of the potentialities and the applications of such methods in others antenna synthesis problem has been carried out referring in particular to the reduction of the sideband radiations in monopulse array antennas in which the difference pattern is obtained by means of sub-arrayed feed network. In the numerical validation, a set of representative examples concerned with the reduction of the sideband levels and the power of the harmonic radiations are reported in order to assess the effectiveness and the flexibility of the proposed approach. Comparison with previously published results are reported and discussed, as well.

In the framework of the synthesis of monopulse array antennas for search-and-track applications, the thesis focuses on the development and the analysis of a method based on the sub-arraying technique aimed at generating an optimal sum and compromise difference patterns through an excitation matching procedure. By exploiting some properties of the solution space, the synthesis problem is reformulated as a combinatorial one to allow a considerable saving of computational resources. Thanks to a graph-based representation of the solution space, the use of an efficient path-searching algorithm to speed-up the convergence of the procedure for the synthesis of large array antennas as well as the use of the Ant Colony Optimizer (ACO) to benefit of its hill-climbing properties in dealing with the non-convexity of the sub-arraying problem are considered. Moreover, a hybrid approach is developed to individually control the level of the secondary lobes. In particular, the sub-array configuration is determined at the first step by exploiting the knowledge of the optimum difference mode coefficients and in the second step, the sub-array weights are computed by means of a quadratic programming procedure. In the numerical validation, a set of representative examples concerned with both pattern matching problems and pattern-feature optimization are reported in order to assess the effectiveness and flexibility of the proposed approach. Comparisons with previously published results are reported and discussed, as well.

In the last decade, nanotechnology has enormously and rapidly developed. The technological progress has allowed the practical realization of devices that in the past have been studied only from a theoretical point of view. In particular we focus here on nanotechnologies for the optical frequency range, such as plasmonic devices and photonic crystals, which are used in many areas of engineering. Plasmonic noble metal nanoparticles are used in order to improve the photovoltaic solar cell efficiency for their forward scattering and electromagnetic field enhancement properties. Photonic crystals are used for example in low threshold lasers, biosensors and compact optical waveguide. The numerical simulation of complex problems in the field of plasmonics and photonics is cumbersome. The dispersive behavior has to be modeled in an accurate way in order to have a detailed description of the fields. Besides the code parallelization is needed in order to simulate large and realistic problems. Finite Difference Time Domain (FDTD) is the numerical method used for solving the Maxwell's equations and simulating the electromagnetic interaction between the optical radiation and the nanostructures. A modified algorithm for the Drude dispersion is proposed and validated in the case of noble metal nanoparticles. The modified approach is extended to other dispersion models from a theoretical point of view. A parallel FDTD code with a mesh refinement (subgridding) for the more detailed regions has been developed in order to speed up the simulation time. The parallel approach is also needed for the large amount of required memory due to the dimension of the analysis domain. Plasmonic nanostructures of different shapes and dimensions on the front surface of a silicon layer have been simulated. The forward field scattering has been evaluated in order to optimize the concentration of the light inside the active region of the solar cell. Some design parameters have been deduced from this study. Opal photonic crystals with different filling factors have been simulated in order to tune the optical transmittance band-gap and find a theoretical explanation to the experimental evidences.

In the framework of the electromagnetic approaches based on learning-by-example (LBE) techniques, this thesis focuses on the development of a strategy for the solution of complex problems by means of support vector machine (SVM). The proposed instance-based classification method compared to more traditional optimization techniques solves the arising quadratic optimization problem with constraints in a simple and reliable way leveraging on the statistical learning theory which enables the design of optimal classifiers with a solid theoretical framework. A set of input/output relations representing the training dataset permits to avoid the a-priori knowledge about the system. By exploiting the generalization capabilities, the robustness against noise and the real-time performance, this technique has been proven to be suitable for more than one real-world application. The investigated problems are addressed by integrating the measured electromagnetic field with a suitably defined classifier that is aimed at defining a real-time reconstruction of the observed domain. For each application field a set of numerical results have been reported in order to assess the effectiveness and flexibility of the proposed approach. The real-time capabilities as well as the feasibility when dealing with real data have been also verified by means of an experimental setup for the passive tracking of non-cooperative targets moving throughout the investigated area.

The study of the next-generation distributed systems for distributed monitoring and user localization in smart environment is treated in this thesis. In the last years, a growing amount of attention has been focused on the adoption of Wireless Sersor Networks (WSN) as a scalable and flexible backbone to implement innovative services in smart environments, like smart building and smart cities. In this framework, this thesis will describe heterogeneous solutions to improve the supervision, control, monitoring, and management of public and private spaces. All these systems exploit the wireless communication and sensing in combination with smart methodologies to provide advanced services to the end user in many application fields, from environmental monitoring to energy management in smart districts or private and public buildings, up to road security and indoor occupancy for management and security reason. The data acquired by the WSN technology are used as input of customized strategies and algorithms developed for the real-time processing, fast analysis and result visualization.

Innovative methodologies for the wireless localization of users and related applications are addressed in this thesis. In last years, the widespread diffusion of pervasive wireless communication (e.g., Wi-Fi) and global localization services (e.g., GPS) has boosted the interest and the research on location information and services. Location-aware applications are becoming fundamental to a growing number of consumers (e.g., navigation, advertising, seamless user interaction with smart places), private and public institutions in the fields of energy efficiency, security, safety, fleet management, emergency response. In this context, the position of the user - where is often more valuable for deploying services of interest than the identity of the user itself - who. In detail, opportunistic approaches based on the analysis of electromagnetic field indicators (i.e., received signal strength and channel state information) for the presence detection, the localization, the tracking and the posture recognition of cooperative and non-cooperative (device-free) users in indoor environments are proposed and validated in real world test sites. The methodologies are designed to exploit existing wireless infrastructures and commodity devices without any hardware modification. In outdoor environments, global positioning technologies are already available in commodity devices and vehicles, the research and knowledge transfer activities are actually focused on the design and validation of algorithms and systems devoted to support decision makers and operators for increasing efficiency, operations security, and management of large fleets as well as localized sensed information in order to gain situation awareness. In this field, a decision support system for emergency response and Civil Defense assets management (i.e., personnel and vehicles equipped with TETRA mobile radio) is described in terms of architecture and results of two-years of experimental validation.