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The Finite-Difference Time-Domain (FDTD) method has become a very powerful tool for the analysis of propagating electromagnetic waves. It involves the discretization of Maxwell's equations in both time and space that leads to a numerical solution of the wave propagation problem in the time domain. The technique's main benefits are that it permits the description of wave propagation in non-uniform media, it can easily accommodate a wide range of boundary conditions, and it can be used to model nonlinear effects as well as the wave behaviour near localized structures or material defects. In this study, we extend this technique to mechanical wave propagation in piezoelectric crystals. It is observed to give large reflection artefacts generated by the computational boundaries which interfere with the desired wave propagation. To solve this problem, the renowned absorbing boundary condition called perfectly matched layer (PML) is used. PML was first introduced in 1994 for electromagnetic wave propagation. Our research has further developed this idea for acoustic wave propagation in piezoelectric crystals. The need to improve the large reflection artefacts by introducing a finite thickness PML has reduced acoustic wave reflection occurring due to practical errors to less than 0.5 %. However, it is found that PML can generate numerical instabilities in the calculation of acoustic fields in piezoelectric crystals. Theses observations are also discussed in this report. / Thesis / Master of Applied Science (MASc)

<p dir="ltr">New classes of electromagnetic modeling problems are arising in the design of quantum information processing technologies. In many cases, these problems involve looking at controlling individual quantum systems with electromagnetic fields at optical frequencies. Since the optical control fields in these applications are essentially classical fields, one promising modeling approach is to perform a semiclassical analysis where the optical fields are treated classically, but the quantum system’s dynamics are modeled quantum mechanically. Typically referred to as Maxwell-Schrödinger models, there is growing interest in these applications to solve the “Maxwell” part of the system directly in terms of the electromagnetic potentials that are used in the Schrödinger equation rather than using the more conventional electric and magnetic fields. To date, the most popular numerical method used to discretize this system of equations is the finite-difference time-domain (FDTD) method. However, these prior works are missing the necessary utilities to consider the modeling of integrated photonic systems when using FDTD methods formulated directly in terms of the magnetic vector and electric scalar potentials. In particular, these potential-based FDTD methods have not been able to model dispersive dielectric materials, which are critical in integrated photonic systems. In this work, we introduce a kind of auxiliary differential equation method for incorporating a Drude-Lorentz-Sommerfeld material model into potential-based FDTD methods. This work also shows the functionality of an absorbing boundary condition for the first time within a potential-based FDTD model to replace the particularly complex implementation of perfectly matched layers within this modeling framework. As such, the methods described in this thesis are intended to help improve the modeling capabilities of potential-based FDTD methods so that they can be used in Maxwell-Schrödinger modeling of more realistic integrated quantum photonic technologies in the future.</p>

Yes / The potentially broad application area in engineering design using Genetic Algorithm (GA) has been widely adopted by many researchers due to its high consistency and accuracy. Presented here is the initial design of a wideband non-dispersive wire bow-tie antenna using GA for breast cancer detection applications. The ultimate goal of this design is to achieve minimal late-time ringing but at higher frequencies such as that located from 4 to 8 GHz, in which is desire to penetrate human tissue for near field imaging. Resistively loading method to reduce minimal ringing caused by the antenna internal reflections is implemented and discussed when the antenna is located in free space and surrounded by lossy medium. Results with optimised antenna geometry and different number of resistive loads are presented and compared with and without existence of scatterers.

Prediction of the sound field in large urban environments has been limited thus far by the heavy computational requirements of conventional numerical methods such as boundary element (BE), finite-difference time-domain (FDTD), or ray-tracing methods. Recently, a considerable amount of work has been devoted to developing energy-based methods for this application, and results have shown the potential to compete with conventional methods. However, these developments have been limited to two-dimensional (2-D) studies (along street axes), and no real description of the phenomena at issue has been exposed (e.g., diffraction effects on the predictions). The main objectives of the present work were (i) to evaluate the feasibility of an energy-based method, the diffusion model (DM), for sound-field predictions in large, 3-D complex urban environments, (ii) to propose a numerical hybrid method that could improve the accuracy and computational time of these predictions, and (iii) to verify the proposed hybrid method against conventional numerical methods. The proposed numerical hybrid method consists of a full-wave model coupled with an energy-based model. The full-wave model is used for predicting sound propagation (i) near the source, where constructive and destructive interactions between waves are substantial, and (ii) outside the cluttered environment, where free-field-like conditions apply. The energy-based model is used in regions where diffusion conditions are met. The hybrid approach, as implemented in this work, is a combination of FDTD and DM models. Results from this work show the role played by diffraction near buildings edges close to the source and near the exterior boundaries of the computational domain, and its impact on the predictions. A wrong modeling of the diffraction effects in the environment leads to significant under or overpredictions of the sound levels in some regions, as compared to conventional numerical methods (in these regions, some differences are as high as 10 dB). The implementation of the hybrid method, verified against a full FDTD model, shows a significant improvement of the predictions. The mean error thus obtained inside the cluttered region of the environment is 1.5 dB. / Master of Science

Parmi les filières de cellules photovoltaïques, les cellules solaires organiques suscitent un intérêt industriel par leur faible coût financier et de production énergétique et leur application possible sur des substrats flexibles de type plastique. L'ITO (Indium Tin Oxide) est l'électrode transparente conductrice (ETC) la plus utilisée pour ces cellules ainsi que pour d'autres dispositifs optoélectroniques. Cependant, ce matériau n'est pas sans présenter certains inconvénients (rareté de l'indium, structure non adaptée à des substrats flexibles,…), et la recherche d'alternatives à l'ITO est une préoccupation actuelle de la communauté scientifique internationale. Une possibilité est alors offerte par des structures multicouches de type Oxyde|Métal|Oxyde. Le rôle des deux couches d’oxydes est d’accorder, en ajustant les épaisseurs, la position, l’intensité et la largeur de la fenêtre spectrale de transmission. Des travaux numériques et expérimentaux couplés ont été effectués en particulier sur les structures SnOx|Ag|SnOx, TiOx|Ag|TiOx et ZnS|Ag|ZnS. Par microstructuration de telles électrodes ou bien par incorporation d’un bicouche Cu|Ag comme feuillet métallique au coeur de la structure, il est possible d’améliorer leurs performances optiques en amplifiant et en élargissant la fenêtre spectrale de transmission, sans dégrader leur haute conductivité. L’intégration d’électrodes SnOx|Ag|SnOx et TiOx|Ag|TiOx au sein de cellules solaires organiques inverses a été entrepris. Des résultats photoélectriques très prometteurs ont été obtenus avec la structure TiOx|Ag|TiOx qui permet d’atteindre des performances de niveau quasi-équivalent aux cellules de référence à base d’ITO. / Among all variants of photovoltaic thins films, organic solar cells generate a major industrial interest due to low manufacturing costs, reasonable levels of energy production and suitability to flexible substrates like plastic. ITO (Indium Tin Oxide) is the most used Transparent Conductive Electrode (TCE) for organic solar cells as well as other optoelectronic devices. However, this material is not without drawbacks (scarcity of indium, non-suitability to flexible substrates...), and the search for alternatives to ITO is actively pursued by the international scientific community. One possibility is offered by Oxide|Metal|Oxide multilayer structures. By reaching the thin metal layer percolation threshold and by varying its thickness, it is possible to obtain very high conductivity and transparency of this multilayer in the visible spectral range. The role of both oxide layers is to tune the position, intensity and width of the spectral transmission window by adjusting the oxides’ thicknesses. Coupled experimental and numerical works were lead in particularly on SnOx|Ag|SnOx, TiOx|Ag|TiOx and ZnS|Ag|ZnS structures. By microstructuring such electrodes, or by incorporating a Cu|Ag bilayer as metal sheet at the core of the structure, it is possible to increase the optical performances by amplifying and expanding the spectral transmission window without degrading the high conductivity. The integration of SnOx|Ag|SnOx and TiOx|Ag|TiOx electrodes in inversed organic solar cells was undertaken. Very promising photoelectric results were obtained with the TiOx|Ag|TiOx structure which allows to reach performances close to that obtained with ITO-based reference cells.