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In this article, 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. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:1019–1024, 2014

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 μ_c=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.

ABSTRACT:Carbon nanotubes are possible building blocks in the development of new generation of electronic devices. The carbon nanotubes allow one fabrication of devices using nanometric scales. They can be used in projects of a wide range of electronic and optoelectronic components such as diodes, transistors and interconnection elements, among others. This paper presents the state-of-the-art of this area, emphasizing the influence of quantum effects on the characteristics of such components.

In this work, we propose and numerically analyze a new electromagnetic polarization filter in THz region based on graphene fish-scale structure. The array is composed by graphene strips placed on a metallized dielectric substrate. The filter can operate in two different frequency regions that can be shifted in frequency by appropriate choice of width of the graphene ribbons. We present as an example, at f 1 5 0.483 THz, the structure possesses the reflection coefficient of 20.38 dB for the incident waves with x-polarization and 248.05dB for the y-polarized ones, while at f 2 5 0.792 THz, the reflection coefficients are 247.25 dB for x-polarization and 20.86 dB for y-polarization. The physics of the device is based on surface plasmon polariton (SPP) resonances in the graphene. The central frequency can be dynamically adjusted by changing the chemical potential (ie, by an external voltage for example) of the graphene strips. K E Y W O R D S fish-scale, grapheme, polarization filter, polarizer, surface plasmon polariton

We suggest and investigate theoretically a new graphene electromagnetic tunable multifunctional component for THz region. The structure represents a planar square array of graphene elements placed on both sides of a thin dielectric substrate. By changing electrostatically the graphene chemical potential, the frequency characteristics of the pass‐band and stop‐band filter can be displaced providing a dynamic control of the filter. This property and combination of a high peak and a deep valley in the transmission response allow one to use the component also as a switch in two different frequency controllable bands. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:1755–1760, 2015

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 () 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.

A new type of the graphene-based three-port circulator is suggested and analysed. The cross-section of the component presents a three-layer structure consisting of a layer of silicon, of silica and of graphene. In-plane figure resembles a common microwave nanostrip circulator with a circular graphene resonator and three waveguides symmetrically connected to it. The graphene is magnetized normally to its plane by a DC magnetic field. The numerical simulation demonstrates the isolation of -15 dB and insertion losses of -2 dB in 6.98 % frequency band with the central frequency 8.23THz.