Navegando por Assunto "Non-reciprocal devices"

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Acesso aberto (Open Access)
Análise comparativa das propriedades ressonantes de nanopartículas e de nanoantenas bowtie de ouro de diferentes geometrias
(Universidade Federal do Pará, 2012-12-14) SANTOS, Thaís Lira Tavares dos; COSTA, Karlo Queiroz da; http://lattes.cnpq.br/7932708321834647; DMITRIEV, Victor Alexandrovich; http://lattes.cnpq.br/3139536479960191
This work presents a comparative analysis of the resonant properties of gold nanoparticles and gold bowtie nanoantennas with new triangular geometries. The proposed geometries are as follows: the curved side triangular ones and the triangular geometries with one corner formed by three tips. The investigated properties are the resonant responses, the spatial distributions of the electric near-field and the resonant wavelengths. The current density inside the nanostructures is also analysed for better understanding of the electric near-field enhancement. For the case of bowtie nanoantennas, the research is also focused on the study of the influence of a silicon dioxide substrate on their resonant properties and on the study of their characteristics in the far-field region (scattering cross section and radiation pattern). The numerical results are obtained in the visible and near infrared regions of the electromagnetic spectrum, simulated by the finite integration technique. For isolated nanoparticles, these results show that the suggested geometries have electric near-field intensity around 160% higher and resonant wavelength redshifted by 15%, as compared to the equilateral triangular geometry. In the case of bowtie nanoantennas, the new geometries have electric near-field intensity 90% higher and resonant wavelength blueshifted by 15%, as compared to the triangular equilateral bowtie nanoantenna. The results of this work can serve for modeling, fabrication and designing of gold nanoparticles and gold bowtie nanoantennas for different applications, for example, microscopy and optical fibre sensors.
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.