Clerisson Nascimento

Graphene nanoantennas with different shapes

In this paper we present a numerical analysis of graphene nanoantennas with rectangular, elliptical, triangular and circular geometries in terahertz band. We model the electromagnetic scattering of these planar structures by the method of moments with the surface impedance of graphene. We analyze the absorbing cross section and the resonances of nanoantennas for different, sizes, chemical potential, temperature and incident angle. The obtained results can be useful to design efficient nanoantennas for terahertz wireless communications.

Planar THz electromagnetic graphene pass-band filter with low polarization and angle of incidence dependencies

We propose and analyze a graphene electromagnetic filter for the terahertz (THz) region. The filter represents a planar square array of graphene elements. A unit cell of the array is formed by two coaxial graphene rings placed on the opposite sides of a thin dielectric substrate. The two electromagnetically coupled rings resonate with dipole plasmonic modes. The rings have slightly different dimensions and consequently different yet close individual resonant frequencies. At a frequency lying between these two resonances, the currents in the two interacting rings have opposite directions. This leads to a suppression of the reflected from the array waves and consequently to a high transmission through the array. For the chemical potential of the graphene μc=0.6 eV, the calculated quality factor of this resonant mode is Q=5 at the frequency f=0.8  THz. At this frequency, the reflection coefficient of the array equals -36 dB and the transmission peak which is defined by the graphene losses is -1.8 dB. We show that the frequency position of the transmission peak can be varied in a wide range by the graphene chemical potential.

Giant Faraday rotation in cross-shaped graphene array in THz region

We study numerically the Faraday effect in cross-shaped graphene array. Our geometrical structure in the optimized configuration can provide the Faraday rotation of about 3° for the frequency 8.9 THz with a relatively low magnetic field of 1T and 13 ° for a magnetic fields of 10 T. These rotation value is about seven times higher than the results published until now. The frequency position of maximum Faraday rotation can be controlled by changing the Fermi energy of graphene or the dimensions of the array.

Extended Group-Theoretical Approach to Metamaterials With Application to THz Graphene Fish-Scale Array

We develop a group-theoretical method for analysis of metamaterials which includes both longitudinal and transversal components of currents in different parts of molecules. In comparison with the existing approach which takes into account only longitudinal components, our method allows one to obtain more information about the properties of metamaterials. As an example of the method application, we suggest and analyze an electromagnetic graphene array for terahertz region. Depending on the parameters of the structure, different types of the absorption resonances can exist in the structure which are discussed from the point of view of symmetry.

Analysis of Electronic Structure of Boron Nitride Nanotubes with Different Positions of Intrinsic Impurities

The pristine boron nitride nanotubes have a large direct band gap around 5 eV. This band gap can be engineered by doping. We investigate electronic structure of the doped hexagonal boron nitride (5,5) nanotubes using the linearized augmented cylindrical wave method. In particular, this work focuses on systematical study of the band gap and the density of states around the Fermi-level when the nanotubes are doped by intrinsic impurities of two substitutional boron atoms in a super cell and a comparative analysis of the relative stability of three structures studied here. This corresponds to 3.3% of impurity concentration. We calculate 29 configurations of the nanotubes with different positions of the intrinsic impurities in the nanotube. The band gap and density of states around the Fermi level show strong dependence on the relative positions of the impurity atoms. The two defect sub bands called Dπ(B) appear in the band gap of the pristine nanotube. The doped nanotubes possess p-type semiconductor properties with the band gap of 1.3-1.9 eV.

Graphene 3-port circulator based on edge-guide mode propagation

In this work we propose and numerically analyze a new type of electromagnetic circulator operating in THz region. The circulator is based on graphene and dielectric substrates. The structure resembles a known three-port microstrip circulator based in edge guided mode. The circulation behaviour is provided by application of a DC magnetic field normal to the graphene plane. In the frequency band (2 ÷ 7) THz the isolation loss of our ultra wideband circulator is −(15 ÷ 50) dB, the insertion loss is −(2 ÷ 5) dB and return loss is better than −10 dB. The chemical potential of the graphene is 0.1 eV and DC magnetic field is 2 T.

Controllable graphene reflect array

We report resonant features of electrically controllable reflect array consisting of continues wavy-shaped graphene strips placed on a thin metal-backed dielectric substrate.

Graphene terahertz filter

In this paper we suggest and analyze numerically an electromagnetic filter for THz region. The filter is made of a frequency selective surface based on graphene elements placed on a dielectric substrate. The unit cell of the device represents a square lattice in which two graphene crosses are placed on both sides of a dielectric substrate. The two graphene elements interact and resonate with two dipole plasmonic modes with different frequencies due to difference in the geometrical sizes of the crosses. In the frequency between these two resonances there is a transparency window that characterizes the filtering property of the device. This effect can be explained by Fano resonance. The device operates at the central frequency 2.3 THz with the reflection and the transmission coefficients equal to -18.6 dB and -0.92 dB, respectively. We show also that the position of the transmission peak can be tuned by changing the chemical potential of the graphene.

THz electromagnetic graphene pass-band filter with polarization insensibility and dynamic control

We suggest and analyze a graphene electromagnetic filter for terahertz region. The filter represents a planar square array of graphene elements. A unit cell of the array is formed by two coaxial graphene rings placed on the opposite sides of a thin dielectric substrate. The two electromagnetically coupled rings resonate with dipole plasmonic modes. The rings have slightly different dimensions and consequently, different but close individual resonant frequencies. At a frequency lying between these two resonances, the currents in the two interacting rings have the opposite directions. This leads to a suppression of the reflected from the array waves and consequently to a high transmission through the array. For the chemical potential of the graphene μc = 0.6 eV, the calculated quality factor of this resonant mode is Q = 5 at the frequency f = 0.8 THz. At this frequency, the reflection coefficient of the array equals to -36 dB and the transmission peak which is defined by the graphene losses is -1.8 dB. We show that the frequency position of the transmission peak can be varied in a wide range by the graphene chemical potential.

Analysis of graphene bow-tie antennas

In this paper, bow-tie graphene antennas of different geometries are suggeted and analyzed. Modifying the antenna geometry one can control the current pathway and, consequently, the antenna resonances.