Programa de Pós-Graduação em Engenharia Elétrica e de Computação
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Doctoral Thesis Análise de biossensores ópticos baseados no efeito SPR utilizando novos modelos de dispositivos quase cristalinos(Universidade Federal do Rio Grande do Norte, 2024-08-30) Cunha, Nilson Henrique de Oliveira; Silva, José Patrocínio da; https://orcid.org/0000-0003-1843-7879; http://lattes.cnpq.br/5753289728835624; https://orcid.org/0000-0003-2919-3515; http://lattes.cnpq.br/7745059963791819; Campos, Antonio Luiz Pereira de Siqueira; Sousa Júnior, Vicente Ângelo de; Mercedes, Cosme Eustaquio Rubio; Andrade, Humberto Dionisio deWith the continuous advancement of new communications technologies across all scientific fields, it is essential that the devices employed keep pace with these developments to ensure reliable results. In this context, applications at very high frequencies have been explored to develop devices with ultra-fast responses. Among these applications, optical sensors have been the subject of extensive research. This work utilizes the Surface Plasmon Resonance (SPR) effect for the analysis of optical sensors based on different models of optical waveguides. The SPR effect occurs when a metaldielectric interface is excited by a light signal at a specific frequency, known as the surface plasmonic frequency, inducing the formation of dense electron clusters in the analysis region, thereby enabling material detection. The objective of this study is to propose and analyze four novel models of plasmonic sensors derived from optical waveguides, including microstructured optical fibers and conventional waveguides. In the first approach, a microstructured optical fiber with elliptical holes was used, exploring two variations: one with an extended core and another with dual cores. The second study involves a microstructured D-type optical fiber, where a defect in the silica (𝑆𝑖𝑂2 ) core was doped with varying concentrations of germanium dioxide (𝐺𝑒𝑂2 ) to optimize the SPR effect. The third proposed structure consists of a rib-type optical waveguide with a microchannel coupled, separated from the guiding region by a thin layer of gold. Lastly, the final proposed structure employs a quasi-periodic microstructured optical fiber, introducing liquid crystal sensitive to temperature variations to enhance the coupling between the fundamental and plasmonic modes. To evaluate the effectiveness of the sensors, the electric (E) and magnetic (H) field distributions, confinement loss (CL) and wavelength sensitivity (WS) were studied. These investigations aim to contribute to the development of advanced optical sensors capable of accurately detecting variations in the refractive index of materials in both chemical and biological applications.Master Thesis Análise de células unitárias com metamaterial utilizando substratos EBG para aplicações em estruturas planares(Universidade Federal do Rio Grande do Norte, 2020-08-26) Cunha, Nilson Henrique de Oliveira; Silva, Jose Patrocinio da; ; http://lattes.cnpq.br/5753289728835624; ; http://lattes.cnpq.br/7745059963791819; Campos, Antonio Luiz Pereira de Siqueira; ; http://lattes.cnpq.br/1982228057731254; Sena, Francisco das Chagas Barbosa de; ; http://lattes.cnpq.br/0166555495027599With the growth of the communications area and the intense study of more efficient ways for the transmission and reception of electromagnetic signals, printed circuits have gained increasing prominence on the world stage, and based on these circuits, the application of artificial materials, they are the metamaterials. The essential difference between conventional materials and metamaterials is that, while conventional materials are defined by their constituent atoms, metamaterials are characterized by their constituent unit cells, in this way, the engineering of the construction of these structures can create an arbitrary response, which would not be achieved with a conventional material. In this context, this work aims to propose the applicability of low-cost metamaterial substrates in planar devices. For that, several analysis models for metamaterial structures will be presented, from the choice of boundary conditions, to the application of the appropriate excitation. After selecting the analysis model, a study will be carried out based on the characterization of a conventional unitary metamaterial cell, based on SRR (Split Ring Resonator) structures. Then, modifications to these cells will be proposed with a change in the resonator geometry, and with the application of EBG (Electromagnetic Band Gap) structures, in order to adapt the frequency responses of the cell to the desired project. Finally, the application of this substrate in a rectangular microstrip patch antenna will be studied, where the reflection coefficient, antenna impedance, gain, radiation diagram, 3dB angle, electric field distribution, on the antenna, the distribution of the surface current density, in the proposed cells, and finally, the Brillouin diagram, to prove the prohibited zones created by the EBG structure, will be analyzed. Thus, it is expected to verify the usefulness and scientific importance of the study proposed in current systems.