Neste trabalho é realizada a otimização de antena de microfita banda larga usando o método de Diferenças Finitas no Domínio do Tempo (FDTD) e software comercial de onda completa. Inicialmente é feita uma introdução sobre o assunto, abordando aspectos de comunicações e de antenas de microfita, além de se fazer uma revisão bibliográfica e resumir o estado da arte sobre o tema do trabalho. A seguir, discorre-se sobre a teoria eletromagnética aplicada a antenas planares. O tópico de base é concluído com síntese dos métodos de simulação usados na análise de antenas de microfita, enfatizando o de FDTD. O próximo item revisa fundamentos teóricos e técnicas aplicadas na obtenção de banda larga em antenas de microfita. O trabalho prossegue com simulações numéricas e medidas da largura de banda, do ganho e da eficiência da antena E e de geometria inovadora aplicando técnica de alimentação capacitiva à antena E. A seguir, o algoritmo genético é apresentado e utilizado na otimização do plano de terra de antena de microfita com alimentação por sonda coaxial e também com alimentação capacitiva, para aplicações em banda larga. Resultados simulados e medidos são apresentados e boa concordância entre eles é obtida. Obteve-se 88% de largura de banda para PIFA com alimentação capacitiva e plano de terra otimizado. A tese é concluída com observações sobre os resultados apresentados e sugestões para prosseguimento e aperfeiçoamento das investigações realizadas. / In the present work, the optimization of broadband microstrip antenna employing the Finite Difference Time Domain (FDTD) and full wave commercial software are presented. First, an introduction on the subject considering main issues in communications and microstrip antennas are described, also a bibliographical review and the state of the art are presented. A review of electromagnetic theory applied to microstrip antenna is presented at the following topic, with emphasis on the FDTD method. The next step is a review of theory and techniques on bandwidth optimization of microstrip antennas. The work follows with numeric simulations and measurements on bandwidth, gain, efficiency of E shapped antenna and with a novel design procedure employing capacitive feeding on the E shapped antenna. The work follows with genetic algorithm being presented and utilized to the optimization of ground plane shape microstrip antenna with coaxial feeding and also with capacitive feeding, aiming to broadband applications. Simulated and measured results are presented. Good agreement is observed. Relative bandwidth of 88% was found for PIFA with capacitive feeding and optimized ground plane. The thesis is concluded with some comments and observations on the results obtained and suggestions for the continuation of the work.

Neste trabalho é apresentada uma análise da antena planar F-invertido (PIFA) com o objetivo de identificar os parâmetros geométricos que influenciam nas características de desempenho: frequência de ressonância, perda de retorno e largura de banda. Para realizar este estudo é desenvolvido um algoritmo em linguagem C baseado no método das Diferenças Finitas no Domínio do Tempo (FDTD). Duas PIFAs de geometria distintas foram investigadas. O primeiro modelo trata da geometria tradicional de elemento irradiador e plano de terra, ambos retangulares. Já o segundo modelo apresenta a fenda em formato de L no elemento irradiador, para operação em frequência dupla, e o plano de terra em formato de T, visando a aumentar a largura de banda. Os resultados da simulação do algoritmo identificam os parâmetros que influenciam no aumento nas duas larguras de banda, e são aplicados na prototipação de uma PIFA GSM-900 e GSM-1800. As medidas de laboratório do protótipo evidenciam os resultados previstos pelo algoritmo. / A Planar Inverted-F Antenna (PIFA) analysis is presented in this work, aiming to identify the geometric parameters that influence the antenna performance, such as resonant frequency, return loss and bandwidth. To accomplish this goal, an algorithm in C language based on the Finite-Difference Time-Domain (FDTD) method is developed. Two PIFAs with distinct geometries are investigated. The first one corresponds to a typicall rectangular patch and ground plane, The second model presents an L-shaped slot for dual frequency band operation, combined with a T-shaped ground plane, in order to increase the bandwidth. The simulated results obtained by algorithm identify the parameters that respond for both bandwidths enhancement, and are applied in a PIFA GSM-900/GSM-1800 practical project. The prototype’s measurements confirm the simulated results.

The diploma thesis deals with the optical response of resonant infrared antennas on silicon dioxide thin film. At first, theory of electromagnetism at metal/dielectric interfaces is described. In the next part, experimental and numerical methods used in the thesis are described and strong coupling between two systems is explained. In the final part of the thesis, the optical response of resonant infrared antennas on a silicon dioxide thin film is studied by Fourier transform Infrared Spectroscopy and FDTD simulations which both show the strong coupling between localized plasmons and phonons in silicon dioxide.

This diploma thesis deals with numerical simulations of the optical response of plasmonic infrared antennas placed on silicon substrates with thin film of silicon dioxide and subsequently with fitting of scattering spectra by model of coupled harmonic oscillators. In this work, we study an influence of length of antennas on the strength of coupling of localized surface plasmons in the antennas with phonons in silicon dioxide film. Also, the influence of silicon dioxide film thickness on this coupling is investigated.

The presented diploma thesis is focused on the Localized Surface Plasmons (LSP). The far-field optical response of the colloidal solutions of gold nanoparticles caused by LSP was investigated and compared with the numerical calculations. For the simulations, the Discrete Dipole Approximation (DDA) and Finite-Difference Time Domain (FDTD) techniques were employed. In particular, the shape and size effects of spherical particles and nanorods were studied. The simulations performed by both methods are in a good agreement for the spheres. For the nanorods, the resonance was found to be affected markedly by their geometry. Also, broader resonance peaks were found. This effect was assigned to the sample size distribution and its influence is discussed by comparing the simulations with experiments. In addition, synthesis of nanorods was carried out as well. Finally, the results on the study of optical properties of silver clusters formed under equilibrium conditions are presented.

Microsized hexagonal gallium nitride pyramids show promise as next generation Light Emitting Diodes (LEDs) due to certain quantum properties within the pyramids. One metric for evaluating the efficiency of a LED device is by studying its Light Extraction Efficiency (LEE). To calculate the LEE for different pyramid designs, simulations can be performed using the FDTD method. Maximizing the LEE is treated as a black-box optimization problem with an interpolation method that utilizes radial basis functions. A simple heuristic is implemented and tested for various pyramid parameters. The LEE is shown to be highly dependent on the pyramid size, the source position and the polarization. Under certain circumstances, a LEE over 17% is found above the pyramid. The results are however in some situations very sensitive to the simulation parameters, leading to results not converging properly. Establishing convergence for all simulation evaluations must be done with further care. The results imply a high LEE for the pyramids is possible, which motivates the need for further research.

The thesis addresses time-domain inverse electromagneticscattering for determining unknown characteristics of an objectfrom observations of the scattered .eld. Applications includenon-destructive characterization of media and optimization ofmaterial properties, for example the design of radar absorbingmaterials.A nother interesting application is the parameteroptimization of subcell models to avoid detailed modeling ofcomplex geometries. The inverse problem is formulated as an optimal controlproblem where the cost function to be minimized is thedi.erence between the estimated and observed .elds, and thecontrol parameters are the unknown object characteristics. Theproblem is solved in a deterministic gradient-basedoptimization algorithm using a parallel 2D FDTD scheme for thedirect problem.This approach is computationally intensive sincethe direct problem needs to be solved in every optimizationiteration in order to compute an estimated .eld.H ighlyaccurate analytical gradients are computed from the adjointformulation.In addition to giving better accuracy than .nitedi.erences, the analytical gradients also have the advantage ofonly requiring one direct and one adjoint problem to be solvedregardless of the number of parameters. When absorbing boundary conditions are used to truncate thecomputational domain, the equations are non-reversible and theentire time-history of the direct solution needs to be storedfor the gradient computation.Ho wever, using an additionaldirect simulation and a restart procedure it is possible tokeep the storage at an acceptable level. The inverse method has been successfully applied to a widerange of industrial problems within the European project,IMPACT (Inverse Methods for Wave Propagation Applications inTime-Domain).T he results presented here includecharacterization of layered dispersive media, determination ofparameters in subcell models for thin sheets and narrow slotsand optimization problems where the observed .eld is given bydesign objectives.

Light-matter interaction in particles of subwavelength size mostly depends on the size, shape, composition of the particles and relies on the properties of incident light. Henceforth, resonant behavior of light can be effectively controlled by changing the aforesaid geometrical parameters. The aim of this study is to investigate the effect of size, shape, and material property dependency on the optimal bounds of scattering and absorption cross-section of nanoparticles. Mie theory is used here to solve Maxwell’s equations of light scattering from nanoparticles of different shape to calculate both scattering and absorption cross-sections of silicon and gold nanoparticles. In this work, numerical analysis based on Finite-Difference Time-Domain (FDTD) method is performed to study the optical properties of different size and shapes of silicon and gold nanoparticles such as sphere, pyramid, ring, and cubical structures. In particular, this study reveals how the resonant behaviour (magnitude and peak position) of light varies in accordance with the change in size, shape and material of a specific particle structured in nanoscale. In conclusion, we can quantify the efficiency of a small absorbing or scattering medium and propose structures suitable for implementation in inverse design applications.

Optofluidic flow-through biosensor devices have been in development for fast bio-target detection. Utilizing the fabrication processes developed by the microelectronics industry, these biosensors can be fabricated into lab-on-a-chip devices with a degree of platform portability. This biosensor technology can be used to detect a variety of targets, and is particularly useful for the detection single molecules and nucleic acid strands. Microfabrication also offers the possibility of production at scale, and this will offer a fast detection method for a range of applications with promising economic viability. The development of this technology has advanced to now warrant a descriptive model that will aid in the design of future iterations. The biosensor consists of multiple integrated waveguides and a microfluidic channel. This platform therefore incorporates multiple fields of study: fluorescence, optical waveguiding, microfluidics, and signal counting. This dissertation presents a model theory that integrates all these factors and predicts a biosensor design's sensitivity. The model is validated by comparing simulated tests with physical tests done with fabricated devices. Additionally, the model is used to investigate and comment on designs that have not yet been allocated time and resources to fabricate. Tangentially, an improvement to the fabrication process is investigated and implemented.

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