Navegando por Assunto "Plasmons de superfície"

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Acesso aberto (Open Access)
Circulador de 4 portas baseado em um ressonador elíptico de grafeno na região terahertz.
(Universidade Federal do Pará, 2020-01-20) OLIVEIRA, Thiago Lima de; DMITRIEV, Victor Alexandrovich; http://lattes.cnpq.br/3139536479960191
A new type of four-port circulator based on graphene for the terahertz frequency range is proposed and analyzed in this work. It consists of two parallel waveguides coupled laterally to a magnetized resonator in the shape of an ellipse. The cross section of the components has a three-layer structure consisting of graphene, silica dioxides and silicon. The graphene resonator is normally magnetized in its plane by an external DC magnetic field. The physical principle of the device is based on the dipolar resonance of the resonant cavity of magnetized graphene. Using the Theory of Magnetic Groups, we were able to analyze the scattering matrices of the symmetry components of the device. In addition, the Temporal Coupled Modes Theory was used in order to analytically analyze the characteristics of the device. The influence of different parameters on the characteristics of the circulator was investigated using the Comsol Multiphysics software. Numerical simulations demonstrate the isolation of ports 3 and 4 around -32.6 dB and -16.2 dB, insertion losses around -2.5 dB, reflection around -20.3 dB and 5.7 % bandwidth with the center frequency of 5.03 THz. The DC magnetic field of applied polarization is 0.8 T. The central frequency of the circulator can be controlled by the change in the Fermi energy of graphene. Finally, a comparison was made between the numerical and analytical model of the device, using the aforementioned tools.
Acesso aberto (Open Access)
Dispositivos não-recíprocos baseados em grafeno na região de THz
(Universidade Federal do Pará, 2019-02-28) CASTRO, Wagner Ormanes Palheta; DMITRIEV, Victor Alexandrovich; http://lattes.cnpq.br/3139536479960191
Four new types of nonreciprocal graphene-based devices operating in the Terahertz region are suggested and theoretically analyzed in this work. They are two three-port circulators with Y and W geometries and two power dividers with different geometries. The cross section of the components has a three-layer structure, composed of graphene, silica and silicon. The planes of the figures of these components consist of a circular resonator of graphene and waveguides connected to it. The graphene resonator is magnetized normally of its plane by an external DC magnetic field, and the physical principle of operation of the devices is based on the dipole resonance of the magnetized graphene resonator. Using the Magnetic Group Theory, we analyze the scattering matrices of the symmetrical components of the devices. In addition, for the analysis of the circulators, the Analytical Temporal Coupled Mode Theory was also used. Numerical simulations were performed by a full wave computational program and the calculations demonstrate isolation levels better than -15 dB for both the circulators and the dividers. The Y-circulator has insertion losses around - 2.6 dB, bandwidth of 7.4% at the center frequency of 5.38 THz, whereas the circulator W showed insertion losses of - 2 dB, bandwidth of 4.5% at the center frequency of 7.5 THz. The DC bending magnetic field in the two cases was 0.45 T and 0.56 T, respectively. The power dividers have shown to posses the division of the signal between the two output ports of -4.4 dB with in the frequency band of 4.5% and 3.4% with magnetic filed of 0,8 T. The influence of geometric and physical parameters on the characteristics of the circulators is discussed. The frequency bands of the devices can be controlled dynamically by changing bias voltage applied between the graphene layer and the substrate.
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.