Navegando por Assunto "Terahertz"

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Acesso aberto (Open Access)
Análise de ressonâncias eletromagnéticas em estrutura periódica de discos de grafeno magnetizadosd na faixa de terahertz
(Universidade Federal do Pará, 2023-02-27) SILVA, Amanda Evangelista da; OLIVEIRA, Cristiano Braga de; http://lattes.cnpq.br/2012907724305086; DMITRIEV, Victor Alexandrovich; http://lattes.cnpq.br/3139536479960191
Since its isolation in 2004, graphene has shown to be a promising material, as it allows strong interaction of charge carriers with terahertz (THz) radiation. This extensive interaction with light is due to the excitation of surface plasmon polaritons (SPPs) thus providing several applications in the areas of THz photonics. In the presence of an external magnetic field, the cyclotron resonance dominates in the THz spectra. In this work we analyze several resonance modes (dipole, quadrupole, hexapole and modes with azimuthal symmetry) that can exist in the graphene disk in an arrangement with periodic square unit cells. We calculated the resonances with magnetization by an external DC magnetic field ranging up to 3T and compared them with the case of the same structure without magnetization where it was observed that the presence of the magnetic field results in the splitting of some resonant modes. The resonant characteristics are numerically obtained using the COMSOL Multiphysics software in two distinct and complementary studies: the eigenfrequency calculation regime referring to the natural modes of resonance and the plane wave excitation with normal incidence. Floquet boundary conditions on the four sides of the unit cells are used to simulate the in-plane periodic structure of graphene. The unit cell side (i.e. the period of the matrix) used in the numerical calculation is A = 9µm, the radius of the graphene disk is D = 3µm. The problem of excitation of some modes is discussed from the point of view of the circular symmetry that, to generate the resonance peaks in this regime, had to be broken through a subtle cut in the shape of a rectangular slit of size Lx = 10nm by Ly = 550nm starting axially from the edge. The disk is modeled as a two-dimensional element, and this provides a good approximation of the atomic thickness of a single layer of this material. Conductivity is modeled by the semi-classical Drude model. The discussion of resonator properties is fulfilled in terms of graphene currents and electromagnetic fields outside graphene. Potential applications of the obtained results are Faraday and Kerr rotators, controllable filters and absorbers for THz photonic circuits
Acesso aberto (Open Access)
Espalhamento eletromagnético no grafeno através de transformadas de impedância
(Universidade Federal do Pará, 2019-02-22) PIRES, Andrey Viana; COSTA, Karlo Queiroz da; http://lattes.cnpq.br/7932708321834647
Graphene is a two-dimensional material with good electrical properties that make possible new telecommunications applications in telecommunications on the terahertz range. This work presents an alternative analysis of the scattering problem in a graphene sheet using the impedance transform. The Green functions, electromagnetic fields and properties of the plasmonic surface wave on the graphene are demonstrated. The numerical results show the spatial field distributions and spectral analysis of the plasmonic wave as a function of media properties, frequency and chemical potential. The results show that the impedance transform is adequate for scattering analysis in graphene sheets because it uses the natural autofunctions of the problem.
Acesso aberto (Open Access)
Estudo de fibras porosas com inclusões metálicas para guiamento em THz
(Universidade Federal do Pará, 2017-09-08) CARDOSO, Markos Paulo; SILVA, Anderson Oliveira; COSTA, João Crisóstomo Weyl Albuquerque; http://lattes.cnpq.br/9622051867672434
The guidance of THz waves has been found of great importance to improve the performance of spectroscopy, imaging and sensing setups. One of the major challenges in designing such structures is the mitigation of the high losses presented by dielectric media in the THz spectral range (0.1 up to 10 THz). This work performs an analytical and numerical modeling of porous fibers with gold inclusions for THz guidance. The design of these metal-dieletric interface is capable to confine THz waves in the air region of the porous fiber, through the excitation of surface plasmons, modes that result from the resonant interaction between the incident electromagnetic radiation and the collective oscillation of free electrons on the metal surface. It is shown that from a suitable design of the gold layer, the effective losses can be reduced and a zero chromatic dispersion can be achieved as result of the coupling between the fiber modes and the surfasse plasmons.