Modeling of radio wave propagation is indispensable for the design and analysis of wireless communication systems. The use of the Finite-Difference Time-Domain (FDTD) method for wireless channel modeling has gained significant popularity due its ability to extract wideband responses from a single simulation. FDTD-based techniques, despite providing accurate channel characterizations, have often employed point sources in their studies, mainly due to the large amounts of resources required for modeling fine geometrical details or features inherent in antennas into a discrete spatial domain. The underlying influences of the antenna on wave propagation have thus been disregarded. This work presents a possible approach for the efficient space-time analysis of antennas by deducing FDTD-compatible macromodels that completely encapsulate the electromagnetic behaviour of antennas and then incorporating them into a standard FDTD formulation for modeling their interactions with a general environment.

Recently, a novel optical imaging technique was successfully used in measuring the functional response of living retinal tissues. The technique, functional ultra high resolution optical coherence tomography, measures localized differential changes in the retina reflectivity over time resulting from external white light stimulation. This result can be used to develop a non-invasive diagnostic method for the early detection of retinal diseases. However, the physiological causes of the experimentally observed optical signals, most of which originate from the photoreceptors layer, are still not well understood. Due to the complexity of the photoreceptors, using purely experimental methods to isolate the changes in light reflectivity corresponding to individual physiological processes is not feasible. Therefore, we have employed the finite-difference time-domain method to model the changes in light scattering patterns of the photoreceptor cells caused by light-induced physiological processes. Processes such as cell swelling, cell elongation and hyperpolarization of doublelipid membrane structures were simulated by changing the size parameters and optical properties of the cells components. Simulation results show that the hyperpolarization of double-lipid membranous structures and cell swelling are the most likely causes for the experimentally observed changes in optical reflectivity. A number of experiments were suggested to verify the conclusions drawn from this numerical work. This numerical work includes an analysis of various errors in FDTD computational models.

Recently, a novel optical imaging technique was successfully used in measuring the functional response of living retinal tissues. The technique, functional ultra high resolution optical coherence tomography, measures localized differential changes in the retina reflectivity over time resulting from external white light stimulation. This result can be used to develop a non-invasive diagnostic method for the early detection of retinal diseases. However, the physiological causes of the experimentally observed optical signals, most of which originate from the photoreceptors layer, are still not well understood. Due to the complexity of the photoreceptors, using purely experimental methods to isolate the changes in light reflectivity corresponding to individual physiological processes is not feasible. Therefore, we have employed the finite-difference time-domain method to model the changes in light scattering patterns of the photoreceptor cells caused by light-induced physiological processes. Processes such as cell swelling, cell elongation and hyperpolarization of doublelipid membrane structures were simulated by changing the size parameters and optical properties of the cells components. Simulation results show that the hyperpolarization of double-lipid membranous structures and cell swelling are the most likely causes for the experimentally observed changes in optical reflectivity. A number of experiments were suggested to verify the conclusions drawn from this numerical work. This numerical work includes an analysis of various errors in FDTD computational models.

A method is presented that allows the use of multiresolution principles in a time domain electromagnetic modeling technique that is applicable to general structures. Specifically, methods are presented that are compatible with the multiresolution time-domain (MRTD) technique using Haar basis functions that allow the modeling of general structures without limiting the cell size to the features of the modeled structure. Existing Haar techniques require that cells be homogenous in regard to PECs and other localized effects (with the exception that permeability and permittivity can vary throughout the cell). The techniques that are presented here allow the modeling of these structures using a subcell technique that permits the modeling of these effects at individual equivalent grid points. This is accomplished by transforming the application of the effects at individual points in the grid into the wavelet domain. There are several other contributions that are provided in this work. First, the MRTD technique is derived for a general wavelet basis using a relatively compact vector notation that both makes the technique easier to understand and allows the differences and similarities between different MRTD schemes more apparent. Second, techniques such as the uniaxial perfectly matched layer (UPML) for arbitrary wavelet resolution and non-uniform gridding are presented for the first time. Using these techniques, any structure that can be simulated in Yee-FDTD can be modeled with Haar-MRTD. For the first time, results for the use of a time-and-space-adaptive grid in an MRTD simulation are presented.

SOI-based micro-ring resonators can be ultra-compact and highly sensitive for sensing applications. In order to obtain deeper notches and enlarge the detection area, the concentric double-ring resonators have been proposed. To further increase the sensing area and promote the sensing sensitivity, we add one more inner ring into the double-ring structure to form the triple-ring resonator. In this thesis, we have derived the transfer functions of the multi-ring structures and calculated the resonance properties of the triple-ring resonators by using the 3-D FDTD method. We have investigated the effects of the ring radius on the transmission spectra and discussed the variations of spectral response between the double-ring and triple-ring resonators. We also demonstrate the applications of the triple-ring resonator as the refractive index sensors. The triple-ring resonator can obtain deeper dips and higher detection sensitivity of 12.85 nm/RIU. Enlarging the gap can increase the sensing area and is shown to be able to promote the sensing sensitivity. Besides, the influences of the light polarization and the optical absorption on the spectral responses have been discussed as well.

¡@In this thesis, a novel subgridding scheme is proposed based on the hybridization of the FDTD and CNDG-FDTD algorithms. The FDTD method is applied to the coarse grid region, while the CNDG-FDTD method is used in the fine grid region. Because of the unconditional stability of the CNDG scheme, the temporal step size can be set equal to that in the coarse grid region to speed up the computation in the fine grid region. Furthermore, the temporal interpolation at the fine and coarse grids interface is no longer necessary and thus the complexity of spatial interpolation is largely reduced. ¡@As the CNDG-FDTD method is free from the CFL condition restraint, it saves a large amount of CPU time. Numerical results agree very well with that of the FDTD scheme. But it requires a larger amount of computer memory, at least 20% more than the FDTD method. A modified version of the CNDG-FDTD scheme with increased memory efficiency is also presented. It has not only eliminated the restraint of the CFL condition, but also achieved a more efficient saving of CPU time and computer memory requirements.

Numerical dispersion resulting from using the second-order central-difference operation to approximate the differential operation is the main error source of the FDTD method. The effect of numerical dispersion can be minimized if the spatial grid size is small than£f/10. It is difficultly to analyze the modeling of electrically large structures since a huge amount of computer memory will be needed if using a very fine grid to discretize the structure. Using higher-order FDTD is the effective alternative to reduce the effect of numerical dispersion. In this paper will discuss the handling of the discontinuous PEC boundary condition in four-order FDTD and its applications to antenna pattern analysis. Using the fourth-order FDTD can enlarge the spatial grid size and reduce the requirement of computer¡¦s memory. The far field range of small size antenna operating at higher frequency is shorter enough to directly derive the far field pattern by enlarging the spatial size of fourth-order FDTD. It will compare the far field pattern derived by four-order FDTD with near-to-far field transformation and analyze their characteristic individually.

We proposes an efficient algorithm for extracting SPICE-compatible circuits of embedded interconnect structures from FDTD-simulated time-domain reflections. A layer-peeling technique (LPT) is used to obtain the time-domain step response of the interconnects under extract (IUE) itself. A pencil matrix method is then used to get the pole-residue representation of the time-domain step response of the IUE. A pole-reducing procedure is implemented based on a bandwidth criterion to simplify pole-residue representation. Finally, the lumped equivalent models of the IUE are synthesized by an equivalent lumped-model extraction technique, in which four types of equivalent model bases are used. The equivalent circuit can be easily implemented in SPICE-like simulator. Several transmission line structures are presented as examples to demonstrate the validity of the proposed algorithm both in time and frequency domains.

Submitted by Alex Sandro R?go (alex@ifpb.edu.br) on 2016-11-23T14:14:27Z No. of bitstreams: 1 An?lise_e_Simula??o_de_Antenas_de_Microfita_Atrav?s_do_M?todo_FDTD.pdf: 6733290 bytes, checksum: d36f54b35c59746e26d58dc9e823c7d6 (MD5) / Approved for entry into archive by Alex Sandro R?go (alex@ifpb.edu.br) on 2016-11-23T14:15:20Z (GMT) No. of bitstreams: 1 An?lise_e_Simula??o_de_Antenas_de_Microfita_Atrav?s_do_M?todo_FDTD.pdf: 6733290 bytes, checksum: d36f54b35c59746e26d58dc9e823c7d6 (MD5) / Made available in DSpace on 2016-11-23T14:15:20Z (GMT). No. of bitstreams: 1 An?lise_e_Simula??o_de_Antenas_de_Microfita_Atrav?s_do_M?todo_FDTD.pdf: 6733290 bytes, checksum: d36f54b35c59746e26d58dc9e823c7d6 (MD5) Previous issue date: 2016-11-23 / Este trabalho tem como finalidade a aplica??o do m?todo das Diferen?as Finitas no Dom?nio do Tempo - Finite Difference Time Domain ? FDTD para an?lise num?rica de antenas de microfita, atrav?s de um programa escrito em linguagem C++. A condi??o de contorno absorvedora necess?ria adotada, para converg?ncia dos resultados, foi a camada perfeitamente casada - Perfect Matched Layer ? PML, posicionada em volta do dom?nio computacional. Para os quatro modelos de antenas propostos, os resultados do par?metro S11 foram encontrados por um programa desenvolvido em linguagem Matlab e os resultados obtidos para os modelos de antenas propostos, foram validados experimentalmente pela constru??o f?sica e medi??o com o analisador de redes vetorial Agilent N5230A e com o software comercial Ansys Design.

De récentes études ont montré que les ondes électromagnétiques, proche d'une structure diffusante telle qu'une pointe de microscope à force atomique (AFM), peuvent être diffusées et détectées en champ lointain. Ainsi, la détection d'ondes de surface par microscopie optique en champ proche (SNOM) est une technique prometteuse dans le cadre des mesures thermiques aux petites échelles. Une telle technologie prend alors le nom de microscope TRSTM (Thermal Radiation Scanning Tunnelling Microscopy).Le travail de thèse présenté dans ce manuscrit se scinde en deux étapes. La première a trait à nos travaux expérimentaux basés sur le montage d'un dispositif TRSTM. Nous en décrivons les différentes composantes, ainsi que les difficultés rencontrées liées à son fonctionnement. En outre, divers outils numériques, destinés à détecter et extraire tout signal périodique utile, sont développés. La seconde étape se concentre sur nos travaux numériques. Nous y proposons un modèle de diffusion d'ondes électromagnétiques basé sur la FDTD (Finite-Difference Time-Domain) et la transformation champ proche/champ lointain. Ce modèle a été validé par l'étude de dipôles, puis de sphères dispersives à proximité d'un substrat diélectrique. Alors, un certain nombre de simulations de diffusion d'ondes évanescentes par une pointe, de diverses formes et de divers matériaux, proche d'une interface, est présenté. / Recent studies have shown that electromagnetic waves (in particular the thermal radiation), in the vicinity of a scattering object such as en atomic force microscope (AFM), can be scattered from near to far-field and thus detected. The detection of surface waves through scanning near-field optical microscopy (SNOM) is a promising technique for thermal measurement at small scales. Such technology is known as TRSTM. The thesis work presented in this manuscript is divided into tow part. The first one relates to our experimental work based on the development of a TRSTM device. Its various components are detailed, and the difficulties observed during its utilization are described. Furthermore, several digital tools, used to detect and extract any useful signal, are presented. The second part of our work focuses on the development of a numerical model based on the finite-difference time-domain (FDTD) and the near-field to far-field (NFTFF) transformation for the scattering of electromagnetic waves. This model has been validated by studying different cases of dipoles and dispersive spheres close to a dielectric substrate. Then, several simulations of scattering of evanescent waves by a tip, with various shapes and materials, near an interface, are presented.