Karlo Q. da Costa

Planar Monopole UWB Antennas with Cuts at the Edges and Parasitic Loops

In this paper, we analyze an antenna for application in ultra wideband systems. This antenna is composed by one planar monopole with cuts at the edges and two parasitic loops. The numerical analysis of the antenna was done by the Method of Moments (MoM). For comparison, some of the calculations were also made by the commercial software IE3D. The results of this analysis show that the antenna has excellent impedance matching in all frequency range of UWB systems.

Comparative analysis of circular and triangular gold nanodisks for field enhancement applications

In this paper, we present a quantitative comparison of circular and triangular gold nanodisks with the same length and thickness. The method of moments is used to solve numerically the scattering problem. With this model, we investigate the spatial near field distribution, spectral response, far field diagrams, and bandwidth wavelength of these particles. Our results show that the resonant wavelength and the near field enhancement and confinement of the triangular particle are larger than those for the circular particle, but the resonance bandwidth and scattering cross section of the triangular particle are smaller.

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.

Analysis of modified bowtie nanoantennas in the excitation and emission regimes

In this work, we analyze modified bowtie nanoantennas with polynomial sides in the excitation and emission regimes. In the excitation regime, the antennas are illuminated by an incident plane wave, and in the emission regime, the excitation is fulfilled by infinitesimal electric dipole positioned in the gap of the nanoantennas. Several antennas with different sizes and polynomial order were numerically analyzed by method of moments. The results show that these novel antennas possess a controllable resonance by the polynomial order and good characteristics of near field enhancement and confinement for applications in enhancement of spontaneous emission of a single molecule.

Numerical analysis of cylindrical nanodipoles by linear moment method

We present a simple and fast method to analyze metallic cylindrical nanodipoles. The model is based on solving numerically the electric field integral equation with linear current approximation, sinusoidal basis functions and finite surface impedance. Some examples of simulations of nanodipoles with different radius and length are presented and compared with the results calculated by software CST. The obtained results show that the proposed model possesses a good efficiency in terms of accuracy and processing time.

Enlarging the impedance matching bandwidth of wire and planar antennas using loop parasitic elements

We present in this work some theoretical and experimental results of utilization of loop parasitic elements in wire (dipole) and planar (patch and monopole) antennas for increasing the impedance matching bandwidth. The antennas were analyzed using our programs, based on the numerical resolution of the electric field integral equation (EFIE) by the method of moments (MoM), and using the commercial softwares IE3D and HFSS. In one of the case studied we compared numerical calculations with experimental data. The obtained results shown that the impedance matching bandwidth can be considerably enlarged with this method.

Development of computational 3D MoM algorithm for nanoplasmonics

In this paper, we present an algorithm for full-wave electromagnetic analysis of nanoplasmonic structures. We use the three-dimensional Method of Moments to solve the electric field integral equation. The computational algorithm is developed in the language C. As examples of application of the code, the problems of scattering from a nanosphere and a rectangular nanorod are analyzed. The calculated characteristics are the near field distribution and the spectral response of these nanoparticles. The convergence of the method for different discretization sizes is also discussed.

Impedance Matching Analysis of Cylindrical Plasmonic Nanoantennas Fed by Optical Transmission Lines

An impedance matching analysis of two plasmonic nanocircuits connected to cylindrical nanoantennas is presented. In the first case, a bifilar optical transmission line (OTL) with finite length is connected between two nanodipoles, where one is illuminated by an optically focused Gaussian beam (receiving dipole) and the other radiates energy received from the OTL (emitting dipole). In the second case, the OTL is fed by a voltage source on one side and connected to a dipole‐loop composed antenna on the other side. These circuits are analysed electromagnetically by the linear method of moments (MoM) with equivalent surface impedance of conductors. Some results are compared using the finite element method. The results show the impedance matching characteristics of the circuits as a function of their geometries and the broadband response of the second circuit due the broadband dipole‐loop antenna.

Broadband Dipole-Loop Combined Nanoantenna Fed by Two-Wire Optical Transmission Line

This paper presents a broadband nanoantenna fed by a two-wire optical transmission line (OTL). The antenna is defined by a combination of a dipole and a loop, where only the dipole element is connected to the OTL. The analysis is fulfilled by the linear method of moments with equivalent surface impedance to model the conductors. Firstly, the nanoantenna alone is investigated, where the input impedance, current distribution, reflection coefficient, fractional bandwidth, radiation efficiency, and radiation pattern are analyzed. Then, the input impedance matching of this antenna with the OTL is considered. In this case the current, near field distribution, radiation pattern, and reflection coefficient are calculated for different geometrical parameters. The results show that the loop inserted in the circuit can increase the bandwidth up to 42% and decreases the reflection coefficient in the OTL to −25 dB.

Combination of electrical and magnetic nanodipoles for broadband applications in optical nanocircuit

This paper presents a theoretical analysis of an optical nanocircuit connected with broadband nanoantenna composed of electric and magnetic nanodipoles with feeding of the electric dipole only. The numerical analysis of the nanoantenna is performed by method of moments (MoM). The calculated results are input impedance, current distribution, reflection coefficient, radiation efficiency, bandwidth, voltage reflection coefficient and electric near field. Comsol Multiphysics software calculates some of these results. The results show that the loop inserted into the circuit increases the bandwidth of nanoantenna and decreases the overall voltage reflection coefficient of the optical nanocircuit.