Split ring resonator (SRR) is a metamaterial structure which displays negative permeability values over a relatively small bandwidth around its magnetic resonance frequency. Unit SRR cells and arrays have been used in various novel applications including the design of miniaturized microwave devices and antennas. When the SRR arrays are combined with the arrays of conducting wires, left handed materials can be constructed with the unusual property of having negative valued effective refractive indices. In this thesis, unit cells and arrays of single-ring multiple-split type SRR structures are numerically analyzed by using Ansoft&rsquo / s HFSS software that is based on the finite elements method (FEM). Some of these structures are constructed over low-loss dielectric substrates and their complex scattering parameters are measured to verify the numerical simulation results. The major purpose of this study has been to establish equivalent circuit models to estimate the behavior of SRR structures in a simple and computationally efficient manner. For this purpose, individual single ring SRR cells with multiple splits are modeled by appropriate two-port RLC resonant circuits paying special attention to conductor and dielectric loss effects. Results obtained from these models are compared with the results of HFSS simulations which use either PEC/PMC (perfect electric conductor/perfect magnetic conductor) type or perfectly matched layer (PML) type boundary conditions. Interactions between the elements of SRR arrays such as the mutual inductance and capacitance effects as well as additional dielectric losses are also modeled by proper two-port equivalent circuits to describe the overall array behavior and to compute the associated transmission spectrum by simple MATLAB codes. Results of numerical HFSS simulations, equivalent circuit model computations and measurements are shown to be in good agreement.

Intrinsically safe (IS) active power supplies subjected to certain transient load conditions can deliver power to a circuit at significantly higher levels than indicated on their nameplate ratings. During a transient load such as an intermittent short-circuit, energy is transferred from the power supply to the short-circuit and an electrical arc may form when the short-circuit is applied or removed. This poses a spark ignition risk as energy is transferred from the arc to the surrounding atmosphere. Currently various International and Australian Standards define the performance requirements for IS electrical apparatus. A duly accredited laboratory is required to establish the intrinsic safety compliance of an apparatus with the Standards. It involves an assessment of the apparatus and may include testing. The assessment of the apparatus determines adequate segregation, separation, construction, and selection of components. The tests performed on the apparatus include a temperature rise test and in some cases, the sparking potential of the circuit is tested using the spark test apparatus (STA). Testing the sparking potential of active power supplies to establish compliance adds significantly to the time and costs involved in establishing compliance. A new alternative assessment method is proposed in this report to augment or replace the testing phase of the compliance certification process for active power supplies. The proposed alternative assessment method (PAAM) is derived from a determination of the steady-state and transient output characteristics of the active power supply under consideration. Parameters such as peak output current, time constant of peak current decay, and the output voltages at these times are measured from the circuit's output characteristics. These measurements can subsequently be used to derive the topology and component values of an equivalent circuit. The resulting equivalent circuit is then considered like a linear power supply and the sparking potential can be determined using existing assessment methods. This thesis investigates in detail the equivalent circuit of a number of direct current (DC) active power supplies whose transient output characteristics exhibit predominantly capacitive behaviour. The results of the PAAM using the equivalent circuit are then compared with results achieved using the current testing procedure with a STA. A small sample of active power supplies is used to generate data from which a relationship between the current testing procedure and the PAAM can be established. The PAAM developed in this research project can be used as a pre-compliance check by designers, manufacturers, or IS testing stations. A failure of this test would indicate that the active power supply's sparking energy is not low enough to be regarded as intrinsically safe. The PAAM requires fewer resources to establish a result than the STA. The benefits of a simplified spark ignition test would flow on from designers and manufacturers to end users.

Les réseaux réflecteurs sont une alternative prometteuse aux antennes à réflecteurs pour la réalisation de diagrammes de rayonnement directifs ou de couvertures formées, notamment dans le spatial ou dans l'aéronautique. Constitués d'un grand nombre de cellules unitaires dont il faut optimiser la géométrie individuellement, ils restent toutefois difficiles à concevoir. Cette thèse traite de la synthèse des antennes réseau à réflecteur. Aujourd'hui les méthodes utilisées pour les concevoir exploitent, pour la majorité, les logiciels de simulation électromagnétique. Elles sont très coûteuses en temps de calcul et requièrent au final des hypothèses simplificatrices. L'objectif de cette thèse est de répondre à la question suivante : est-il possible de synthétiser de manière purement·analytique un réseau réflecteur? Nous avons répondu à cette question en exploitant la méthode de modélisation multimodale. Elle consiste à représenter la cellule unitaire sous la forme d'un circuit équivalent. Ses propriétés remarquables permettent de prédire analytiquement la phase en réflexion en fonction des dimensions de la cellule unitaire. Un réflecteur composé de cellules unitaires à motif 1 D de;type ruban métallique a tout d'abord été étudié et évalué dans le cadre de la synthèse analytique d'une structure simple. Cette étude a permis de valider la méthode de modélisation en vue de son utilisation dans la synthèse analytique de réseaux réflecteurs. Trois réseaux réflecteurs composés de cellules unitaires 2D de types patch et grille ont ensuite·été synthétisés sur la base de trois spécifications différentes, ceci afin de tester la synthèse analytique dans des configurations de plus en plus contraignantes. Finalement il s'est révélé que la méthode de modélisation multimodale et prometteuse mais que sa précision doit encore être améliorée pour permettre une synthèse complète de réseau réflecteur. / Reflectarrays antennas are a promising alternative to reflector antennas in order to produce focused and contoured beams especially for aeronautics and space applications. A reflectarray antenna is made up of ah array of unit cell that provide a pre-adjusted phasing to form the desired beam.The synthesis of a reflectarray consists in fixing the geometrical dimensions of each unit cell to generate the desired phase law. This thesis focuses on the synthesis of reflectarray. The current methods are mostly based on full­wave analysis and so they are time consuming.The purpose of this thesis is to answer at the following question: a reflectarray can be fully analytically synthesized? We answer it by using the multimodal method. The unit cell is then represented by an equivalent circuit. Using its remarkable properties, the reflected phase can be analytically predicted according to the geometrical dimensions of the unit cell. We used it firstly to synthesize a reflector where the unit cell is composed or a metallic strip. This study has validated this method in order to synthesize reflectarray, Then three reflectarrays have been synthesized based on three specifications. Finally, the multimodal method is promising but the precision has to be improving in order to fully synthesize a reflectarray.

Frequency response analysis (FRA) of transformers is universally accepted as a highly sensitive tool to detect deformations in its windings. This is evident from the fact that customized commercial equipment (popularly called FRA or SFRA instruments) are used and recently the IEEE has issued a draft trial-use guide. Nevertheless, use of FRA is still limited to only detection and there is little progress towards its use for localization of winding deformation. Toward this end, a possible approach would be to compare the healthy and deformed systems in a suitable domain, e.g., their respective models could be compared. In this context, the mutually-coupled ladder network is ideally suited because not only does it map the length of the winding to sections of the ladder network, but, also inherently captures all subtle intricacies of winding behaviour under lightning impulse excitations insofar as the terminal response, internal oscillations and voltage distributions are concerned. The task of constructing a ladder network from frequency response is not trivial, and so exploration of newer methods is imperative. A system can comprehensively be characterized by its frequency response. With this as the starting point, many approaches exist to construct the corresponding rational function (in s-domain). But, the subsequent step of converting this rational function into a physically-realizable mutually-coupled ladder network has, as yet, remained elusive. A critical analysis of the circuit synthesis literature reveals that there exists no analytical procedure to achieve this task, a fact unequivocally stated by Guillemin in his seminal book "Synthesis of Passive Networks". In recent years, use of iterative methods to synthesize such ladder networks has also been attempted with some degree of success. However, there exists a lot of scope for improvement. Based on this summary, the objectives of this thesis are as follows- _ Development of an analytical procedure, if possible, to synthesize a mutually-coupled ladder network starting from the s-domain representation of the frequency response _ Construction of a nearly-unique, mutually-coupled ladder network employing constrained optimization technique and using frequency response as input, with time-efficiency, physical realizability and repeatability as its features In Chapter 2, analytical solution is presented to convert a given driving-point impedance function (in s-domain) into a physically-realizable ladder network with inductive couplings (between any two sections) and losses considered. The number of sections in the ladder network can vary, but, its topology is assumed fixed. A study of the coefficients of the numerator and denominator polynomials of the driving-point impedance function of the ladder network, for increasing number of sections, led to the identification of certain coefficients, which exhibit very special properties. Generalized expressions for these specific coefficients have also been derived. Exploiting their properties, it is demonstrated that the synthesis method essentially turns out to be an exercise of solving a set of linear, simultaneous, algebraic equations, whose solution directly yields the ladder network elements. The proposed solution is novel, simple, and guarantees a unique network. Presently, the formulation can synthesize a unique ladder network up to 6-sections. Although it is an analytical solution, there are issues which prevent its implementation with actual FRA data. Keeping the above aspect in mind, the second part of the thesis presents results of employing an artificial bee colony search algorithm for synthesizing a mutuallycoupled lumped-parameter ladder network representation of a transformer winding, starting from its measured magnitude frequency response. The bee colony algorithm is modified by defining constraints and bounds to restrict the search-space and thus ensure synthesis of a nearly-unique ladder network, corresponding to each frequency response. Ensuring near-uniqueness while constructing the reference circuit (i.e., a uniform healthy winding) is the objective. The proposed method is easy to implement, time-efficient, ensures physical realizability and problem associated with supply of initial guess in existing methods is circumvented. Experiments were performed on two types of actual, single, isolated transformer windings (continuous-disc and interleaveddisc) and the results are encouraging. Further details are presented in the thesis.

The Master‘s thesis deals with the topic of perovskite solar cells with the main focus on the materials used for the active layer. In the introductory part, the electrical and optical properties of halide perovskites are described and specific examples of perovskite crystals are introduced. The description of impedance and photoimpedance measurement methods used for characterization of perovskite solar cells is also included in the thesis. The measurement of electrochemical impedance spectroscopy was conducted on four perovskite crystals and equivalent circuit was formed to fit the obtained data. Parameters of the circuit elements were acquired using the fitting method and were further evaluated in experimental part of this thesis.

State-of-the-art Li-ion cathode materials are based on LiMO2 (M=Ni, Mn, Co) layered transition metal oxides (denoted NMC) with Ni-rich composition because of their high specific capacity. Yet, these materials suffer from poor capacity retention due to crack formation during de-/lithiation cycling. Particle cracking leads to exposure of new electrode surface which leads to Li-inventory loss, increased side reactions, and electric disconnection. Quantification of the extent of cracking is therefore desirable, especially during in situ whilst cycling of the Li-ion cell. Herein, we evaluate and improve an analytical methodology based on electrochemical impedance spectroscopy (EIS) in order to estimate the changes in electrochemically active surface area of both poly- and single-crystalline Ni0.8Mn0.1Co0.1(NMC811) active materials. A transmission-line model (TLM) applied to both non-blocking and blocking electrode condition was utilized in order to deconvolute and interpret the acquired experimental data. Fits of the complex TLM equivalent-circuits to the impedance spectra was facilitated by developing a global stochastic iterative function based on local multivariate optimization. Impedance analysis during short- term cycling showed that the single-crystalline NMC811 suffered from less particle cracking and side reactions compared to polycrystalline NMC811, which was also confirmed from post-mortem gas adsorption analysis. A novel approach to estimate the extent of particle cracking in commercial Li-ion cells by utilizing an empirically strong positive correlation between the charge-transfer capacitance and resistance was proposed. The work presented herein demonstrates the unique prospects of the EIS methodology in the development and research of future rechargeable batteries

<div>The high-frequency switching of transistors in power electronic (PE) converters is known to cause unintended common-mode (CM) current that flows through parasitically-coupled ground paths. One way to model these currents is to utilize time-domain simulations that capture switching dynamics and the corresponding parasitic response. Although potentially useful, the small time steps required can create a computational burden and limit the usefulness of the approach. In addition, access to internal hardware needed to characterize parasitic parameters is often limited.</div><div><br></div><div>In this thesis, frequency-domain Thevenin equivalent circuits (TECs) are derived to model the CM behavior of PE converters. To do so, periodic linear time-varying (PLTV) analysis is used to develop Thevenin-like models that account for switching behavior of PE circuits. Subsequently, it is shown that in many applications these PLTV TECs can be reduced to traditional linear time-invariant (LTI) forms. Methods to experimentally characterize LTI TEC parameters and couple multiple TECs together for system-level analysis are then established. Finally, the TEC approach is extended to model converters in which common- and differential-mode (CM/DM) behavior are strongly coupled. Simulation and experimental results are used to validate the proposed TEC techniques.</div>

Following the positive reception of electric and hybrid transport solutions in the market, manufacturers keep developing their vehicles further, while facing previously undertaken challenges. Knowing the way lithium-ion batteries behave is still one of the key factors for hybrid electric vehicles (HEVs) development, especially for the requirements of the battery management system during their operation. Hence, this project focuses on the necessity of robust yet reasonably simple and cost-effective models of the battery for estimating the health status during the operation of the vehicles. With this aim, the procedure and models to calculate the state-of-health (SOH) indicators, internal resistance and capacity, are proposed and the results discussed. Two machine-learning based models are presented, a support vector machine (SVM) and a neural network (NN), together with one equivalent circuit model (ECM). The data used for training and validating the models comes from testing the batteries in the laboratory with standard performance tests and real driving cycles along the battery lifespan. However, data sets measured in actual heavy-duty vehicles during their operation for three years is also analysed and compared. With respect to this matter, a study of the battery materials, behaviour and operation attributes is carried out, highlighting the main aspects and issues that affect the development of the models. The inputs for the models are signals that can be measured on-board in the vehicles, as current, voltage or temperature, and other derived from them as the state-of-charge (SOC) calculated by the internal battery management unit. Time-series of the variables are used for simulation purposes. The management of signals and implementation of the models is done in the environment of Matlab-Simulink, using some of its in-built functions and other specifically developed. The models are evaluated and compared by means of the normalized root mean squared error (NRMSE) of the voltage output profile compared to that of the tested batteries, but also the error of the internal resistance calculations calculated from the voltage profile for the three models, and the internal parameters in case of the ECM. While despite the difficulties faced with the data, the models can eventually perform accurate estimations of the resistance, the results of the capacity estimations are omitted in the document due to the lack of useful information derived. Nevertheless, the calculation procedure and other considerations to take into account regarding the capacity estimation and data sets are undertaken. Finally, the conclusions about the data used, battery materials and methods evaluated are drawn, laying down recommendations as to design the performance tests following the conditions of the driving cycles, and indicating the higher general performance of the SVM respect the other two methods, while asserting the usefulness of the ECM. Moreover, the battery with NMC material composition is observed to be easier to predict by the models than LFP, also showing different evolution of its internal resistance.

Using a near-field array of acoustic resonators, it is possible to modify a focused pressure field and enforce a spatial frequency corresponding to the resonator array spacing. This higher spatial frequency makes it possible to focus and image with a resolution that is better than if the focusing were in free space. This near-field effect is caused by the phase shifting properties of resonators and, specifically, the delayed phase found in waves with a temporal frequency lower than that of the resonators in the array. Using time reversal, arrays of resonators are explored and the subwavelength focusing is used to describe the ability to image subwavelength features. A one-dimensional equivalent circuit model accurately predicts this interaction of the wave field with an array of resonators and is able to model the aggregate effect of the phononic crystal of resonators while describing the fine spatial details of individual resonators. This model is validated by a series of COMSOL full-wave simulations of the same system. The phase delay caused by a single resonator is explored in a simple experiment as well as in the equivalent circuit model. A series of experiments is conducted with a two-dimensional array of resonators and complex images are produced which indicate the ability to focus complex sources with better resolution.

Li-ion batteries (LIB) are used in many applications because of their high-power/energy density, long life cycling, and low self-discharge rate. The use of LIB continues to grow every day, and the necessity for proper safety standards grows as well. A key aspect for safe utilization of LIB is determining their safety and remaining useful life (RUL). Battery characteristics degrade over time under normal and extreme operating conditions and modeling the electrochemical processes can improve RUL estimations. Extreme operating conditions such as abnormal temperatures and charge/discharge rates are believed to exacerbate the rate of degradation. Li-ion batteries are also susceptible to mechanical damage, which may lead to an electrical short. In severe cases, mechanical damage causes a thermal run away, and possibly explosions or fires. In the event of a car accident, battery packs can be damage without an electrical short or immediate thermal run away. Currently, there is no reliable batt / Mechanical Engineering