Carbon Nanotube Dipole Research Articles

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%.

Effect of the radius on the resonance properties of carbon nanotube dipole antennas

The resonance characteristics of dipole antennas based on armchair carbon nanotube are numerically investigated. The analysis takes into account the interaction of electrons with acoustic phonons which leads to the dependence of the electron relaxation time on the radius of the nanotube. The input impedance of the nanoantena as a function of the frequency of an incident electromagnetic field in the GHz range is obtained by the numerical solution of the Hallen’s integral equation. The dynamic quantum mechanical conductivity of armchair carbon nanotubes is used including the explicit dependence of the relaxation frequency on the radius. In this way, it is adequately described the resonant activity of the nanoantenna depending on the radius and length of the carbon nanotube. Current distributions are presented.

Pole-zero analysis and wavelength scaling of carbon nanotube antennas

Carbon nanotube (CN) antennas have applications in the THz electromagnetic spectrum. Nanotubes have a highly dispersive and frequency dependent conductivity model. In this article, we compare the poles and zeros in the input impedance of CN antennas at different lengths. We used model-based parameter estimation to approximate the input impedance of the antenna with a rational function in the complex frequency domain. Despite dispersive conductivity of CN, the imaginary part of the poles and zeros are respectively the integer multiples and odd multiples of the imaginary part of the first pole and zero. However, the real part of poles is almost constant, while the pattern was not observed for the real part of zeros. We also show that CN dipoles operating between 43 and 53 GHz are well matched if the source impedance is much higher than 50 ohms, and even higher than 12.9 kΩ. The fundamental resonances (f0) of CN dipoles plotted versus their inverse-half-length (1/L) are linearly related, but the intercept of the fitted straight line is non-zero unlike that for perfect electric conductor (PEC) dipoles. This leads to non-linear variation in wavelength scaling of CN dipoles. The resonant CN antennas are relatively much shorter than PEC dipoles.

Effective wavelength and resonance characteristics of carbon nanotube optical antenna

The effective wavelength scaling theory for optical antennas indicates that an optical antenna does not respond to the wavelength of incident electromagnetic wave, but to a shorter effective wavelength which depends on the plasma wavelength and optical dielectric permittivity of the antenna material, and also on the geometric structure of the antenna. In this paper, based on the effective wavelength scaling theory for optical antennas and on the assumption that metallic carbon nanotube (CNT) can be described by a free electron gas according to the Drude model, the general relationship between effective wavelength and dielectric properties of the antenna material for a metallic carbon nanotube optical antenna is derived. According to this relationship, the investigation into the effective wavelength that a metallic CNT optical antenna responds to can be transferred to easier theoretical calculation for the dielectric properties of CNT, instead of exploring its plasma wavelength. Following first-principle calculations for dielectric properties of CNT with 4 diameter, the effective wavelength versus incident wavelength for each of two types of metallic 4 CNT antennas is investigated. In addition, the resonance characteristics of metallic 4 CNT dipole antennas are analyzed. It is shown that the effective wavelength approximately follows a linear relationship with wavelength of the incident light for the 4 metallic CNT antenna, which is consistent with the wavelength scaling theory. In addition, CNT optical antenna has good wavelength scaling performance compared with nano-antennas made of conventional metals like silver and gold; hence metallic CNTs as optical antennas are beneficial for constructing more compact devices. Moreover, according to the simulation results of resonance characteristics of metallic 4 CNT dipole antennas, there are several 4 metallic CNT dipole antennas with small difference in length meeting the resonance conditions for incident electromagnetic wave with a certain frequency, while there are one or more corresponding resonant modes in the optical and near-infrared spectral range concerned for a 4 metallic CNT dipole antenna with fixed length. Therefore, it is easier to meet the resonance conditions for CNT optical antenna than for conventional metal optical antenna, which also arises from the superior wavelength scaling ability of CNT. These advantages of CNT can help to miniaturize the optical antenna and improve the efficiency of energy conversion of the incident radiation in the optical and near-infrared spectral range. Reliability of the assumption and the theoretical process in this paper are validated by comparing the simulation results with existing investigations. Therefore, the theoretical investigations in this paper may provide a new approach to studying metallic CNT optical antennas. The simulation results also demonstrate the potential applications of CNT optical antenna, including solar energy harvesting and conversion.

Marching-on in degree method for electromagnetic coupling analysis of carbon nanotubes (CNT) dipoles array

Transient electromagnetic analysis of carbon nanotubes (CNT) dipoles is presented. The thin wire approximation and the scattering theory are employed to formulate the problem. Therefore, an accurate system of coupled time domain electric field integral equations (TD-EFIE) is developed in order to predict the responses of the CNT dipoles excited by transient electromagnetic waves. To obtain stable and accurate solutions based on proposed system, the marching-on in degree method is applied with piecewise functions as space basis and weighted Laguerre Polynomials as temporal basis. Numerical results involving transient currents on each CNT dipole are presented. The electromagnetic coupling analysis between the CNT dipoles is conducted depending on the separate distances and the number of the CNT dipoles. Hence, the physical coupling effects are proved.

Electrodynamic analysis of nanoantennas at millimeter and optical wavelength ranges

Electrodynamics models and radiophysical properties of carbon nanotube-dipoles (isolated on the substrate lattices), metallic optical antennas and optical antennas, formed from ZnO nanorods coated with metal films were developed and investigated. The models are based on numerically analytical solution of integrodifferential equations describing the diffraction of electromagnetic waves on impedance and dielectric bodies. The use of integral representations of the kernels of integrodifferential equations allowed us to overcome the difficulties of solution, associated with the singularity of kernels and to reduce the computation time by an order of magnitude.

Synthesis and Characterizations of ZnO Nanoparticles for Application in Electromagnetic Detectors

Electromagnetic (EM) waves are able to distinguish between water and hydrocarbons due to their high difference in resistivity value. The method that uses EM technology to explore hydrocarbon is called Seabed Logging (SBL). Due to high demand of hydrocarbons, improvement of this technology is needed. The paper consists of modelling of the prototype of EM transmitter and receiver for hydrocarbons exploration. EM transmitter consists of carbon nanotubes (CNT), aluminium wire with magnetic feeder in toroidal shape. ZnO-CNTs-PVDF composites are used for EM detection. The XRD analysis showed a clear diffraction peak of [101] plane at 36°C of the 2θ. Raman spectra were obtained for ZnO synthesised at 200°C and 300°C temperatures. The initial permeability, Q-factor and relative loss factor were measured using vector network analyser. Results show high value of Q-factor (~43) of the ZnO-CNTs at frequency between 20-30 MHz. The nanoparticles also show low relative loss factor for frequencies above 10 MHz. The grain size, morphology and shape of the particles were characterized using FESEM and revealed rod-like structures. The CNT dipole transmitter system using improved CNT dipole antenna and CNT-ZnO detector record an enhancement of 192% and can be used for hydrocarbon detection.

TDIE Modeling of Carbon Nanotube Dipoles at Microwave and Terahertz Bands

In this letter, a novel procedure is introduced for the simulation of carbon nanotube (CN) antennas directly in the time domain. This formulation is based on the time-domain electric-field integral equation (TD-EFIE) for thin-wires, including external loads. Appropriate loads have been derived to match the physical response of single-walled CN media to external electromagnetic fields. The results show good agreement with a validated frequency-domain formulation. The time-domain formulation provides physical insight into the well-known characteristic effects of CN dipoles, such as slow-wave propagation and the existence of low-frequency resonances.

Terahertz performance of single-walled carbon nanotubes and arrays

A new carbon nanotube antenna to generate terahertz waves is proposed. The typical properties of terahertz radiation from carbon nanotube dipole antennas have been investigated based on finite integral methods. The terahertz pulses emitted from carbon nanotubes and the terahertz amplitude spectrum have been analysed for carbon nanotubes with a length of 15 μm and a radius of 2.712 nm. Other properties such as current distributions, electrical field distributions and scattering parameters are also presented. For a single-carbon nanotube dipole, the gain is very low due to its extremely small radius. Therefore, carbon nanotube arrays have been proposed in order to improve the gain and efficiency. The results could be useful for the design of the future nano-antennas at terahertz range.

Terahertz radiation from armchair carbon nanotube dipole antenna

This paper investigates the electromagnetic radiation characteristics of a metallic, large aspect ratio single walled carbon nanotube antenna in the terahertz frequency region below 12.5 THz. The key features of terahertz pulse have been revealed on the carbon nanotube antenna in comparison with conventional photoconductive switching. The terahertz waveforms, radiation power and their field distributions have been evaluated and are analysed. The Fourier transformed spectra over the whole frequency range demonstrate that the carbon nanotube antenna can be used as radiation source for broadband terahertz applications.

Radiation Properties of Carbon Nanotubes Antenna at Terahertz/Infrared Range

The geometric structure and the terahertz/infrared radiation characteristics of carbon nanotubes dipole antenna arrays have been investigated by CST MICROWAVE STUDIO based on finite integral methods. In terahertz and infrared frequency span, the antenna properties such as electrical field distributions, scattering parameters, standing wave ratio, gain, and two dimension directivity patterns are discussed. Our results show that N × N antenna arrays have higher radiation efficiency than single carbon nanotube dipole antenna.

Infrared and Optical Properties of Carbon Nanotube Dipole Antennas

The characteristics of armchair carbon nanotube dipole antennas are investigated in the infrared and optical regime. The analysis is based on a classical electromagnetic Halleacuten's-type integral equation, and an axial quantum mechanical conductance function for the tube. It is found that, within a certain frequency span in the GHz-THz range, finite-length carbon nanotube dipoles resonate at approximately integer multiples of one-half of a plasma wavelength. Outside of this range, current resonances are strongly damped. In the optical regime, antenna properties are strongly modulated by interband transitions. General antenna characteristics of finite-length carbon nanotube dipoles are presented, such as input impedance, current profile, gain, and efficiency, and radiation patterns are discussed