Design of Carbon Nanotube Antenna in Nanoscale Range

In this paper, new values of efficiency for coated and non-coated carbon nanotube dipole antennas are found at different ranges of length and constant radius to have an effective model in wireless communication technology, biomedical engineering, sensors and solar cells. The main issue is to get matching between the antenna and the feeding source (discreet port). To have the best value of matching impedance by optimization method through entering trials of impedance value the aim of this paper is to have the best result of efficiency in each length. A new value of efficiency is shown for coated carbon nanotube dipole antennas, it is about 59%.

Open Journal of Antennas and Propagation characterize the THz antenna based on combining the Boltzmann transport equation and Maxwell's equations with boundary conditions of the electron distribution function [3]. The performance of CNTs dipole antennas has been investigated using comprehensive numerical techniques. In this paper, a virtual CNTs model is developed to be used with commercial software packages to deduce the performance of various CNTs antenna configurations. There are several methods for the investigation of the properties of the CNTs antenna [1].
The complex permittivity approach has been adopted to know the constitutive parameters of the antenna material that will be modeled to become ready for the simulation. Quantitative predictions of the performance of CNTs antenna dipoles, including input impedance, and efficiency, are presented as a function of frequency [4] [5].
New material structure (NMS) is presented to enhance antenna properties consisting of SWCNTs dipole antenna coated by a thin layer (in nm scale) of several materials separately as aluminum or copper. The simulation of the equivalent modeling approach for SWCNTs-composite material is illustrated.
The study of their EM properties is very important to offer new material for antenna design at different applications [6]. In order to predict the EM behavior of the SWCNTs-composite material, the important parameters of this material have been extracted. Hence, these parameters are utilized to represent the equivalent modeling approach of SWCNTs [7] [8].
Computer Simulation Technology is a powerful numerical full electromag- The trails of having a dipole antenna with the efficiency higher than the copper one have been made by researchers in recent years [1]. Copper dipole antenna does not offer reliable efficiency when it transmits or detects terahertz frequency signal because of skin effect. The idea of using SWCNTs dipole antenna without any skin effect has been established to develop the dipole antenna and have a small size lightweight prototype. But the value of efficiency does not reach the desired goal. However, the previous study has shown that the radiation efficiency of a single-walled carbon nanotube (SWCNT) antenna is very low, which is mainly attributed to the strong retarded surface wave that reduces the radiation resistance. On the other hand, the problem of impedance mismatch is significant if a single CNT is used to build an antenna because its characteristic impedance (10 -100 kΩ) is extremely large compared to the normal feeding line (50 Ω) [1]. Because of this, the idea of coating SWCNT has been studied to have dipole antenna works on the high frequency with probable efficiency [9]. Optimization method is the way that has been approved to solve the problem of impedance mismatch. Open Journal of Antennas and Propagation

Structure of Proposed Composite Material
Composite material in the 3D EM computer simulation technology (CST).
Where, this equivalent model is equivalent bulk material (EBM). The EBM model has the same properties of SWCNTs composite material such as, effective conductivity, complex permittivity, plasma frequency, and relaxation frequency.
Therefore, by inserting these material parameters in the available 3D EM simulation software packages, the EBM model can be designed and implemented [7] [9].
Complex permittivity approach had been applied to predict the electromagnetic properties of SWCNT-copper dipole antennas. Through previous approach, Drude dispersion model was adopted and effective parameters were calculated using Equation (2) and Equation (4). The values of plasma frequency and relaxation frequency were calculated as

Methodology
In this paper, a new material structure (NMS) is presented to design a dipole antenna for wireless antenna applications at THz frequency band and fulfill the required enhancement for the antenna properties. The effective model approach will be used for modelling the NMS [9].

Mathematical Analysis of SWCNT-Composite Material
First step of modeling SWCNTs to create CNTs on software package (CST), the method of defining SWCNTs by using complex permittivity approach in two ways either by Discrete values of and tabulated in dielectric dispersion fit window and computed using MATLAB codes, or by Drude dispersion model have been discussed. The electrical conductivity is an important property of the NMS (SWCNTcomposite material). Similarly, the influences of the SWCNT and layer of coated material are related significantly to the electrical conductivity of the NMS. Therefore, the estimation of this property is for the new structure.

Drude Dispersion Model
Mathematical dispersion formulas in Drude Dispersion model have been used to evaluate the material's optical properties by adjusting specific set parameters. Drude's model is based on the kinetic theory of electrons in a metal which assumes that the material has motionless positive ion and non-interacting electron gas using classical mechanical theory of free electron to explain the transport properties of conduction electrons in metals, conductive oxides, and semiconductors.

Simulation Modelling Approach of New Material Structure
In modern research of antenna applications, the investigation of electromagnetic properties is very important. Complex permittivity approach has been applied to predict the electromagnetic properties of the CNT antennas [5] [8]. Through the previous approach, Drude dispersion model is adopted and effective parameters are calculated. Mathematical dispersion formulas in the Drude Dispersion model have been used to evaluate the material's optical properties by adjusting specific set parameters. The value of epsilon infinity is one for all types of CNTs. The value of plasma frequency for SWCNTs antenna without coating and with coating material is computed from Equations: where, f V is the Fermi velocity for CNTs, r is the radius of CNTs and t is the

Matching Impedance of Antenna Model
Matching issue between antennas and the feeding source (discreet port) is one of the main problems of SWCNTs dipole antenna and SWCNTs-composite dipole antenna. This matching approach depends on changing the Normalized Fixed Impedance (NFI) of the parameter to balance the effectiveness of the input impedance of these dipole antennas with the internal impedance of the feeding source [4] [7] [11]. Optimization method is the way that had been presented to find the most suitable impedance that matched perfectly to have the most effi- permittivity (real part) at almost 1 THz has been obtained as 228.51. While the imaginary part of permittivity is equal to 23589.

Efficiency
The radiation efficiency of SWCNTs antenna had very low values that restricted its application as an antenna in the THz regime. SWCNTs-composite material is used to increase the radiation efficiency very significantly in the THz regime. By using the steps followed to define SWCNTs-composite dipole antenna in previous researches. SWCNTs-copper dipole antenna was created and the required simulation steps have been followed [6]  The highest value of radiation efficiency has been obtained in this paper at 30 μm length, and it is equal to 59.14%.

Conclusions
In this paper, the efficiency of SWCNTs-coated and non-coated dipole antennas as a function of frequency are found at different ranges of length and constant  radius. The result shows new values of efficiency for coated carbon nanotube dipole antenna, it is about 59% in the case of zero loss and 77% in the case of loss due to miss matching impedance. In future work, the aspiration is to design a terahertz antenna that will use in biomedical engineering very efficiently to get the devices as small as possible with higher efficiency values and faster data rate in form of 0D Graphene terahertz antenna that radiated EM waves isotropically.