899 research outputs found
Applications of Graphene at Microwave Frequencies
In view to the epochal scenarios that nanotechnology discloses, nano-electronics has the potential to introduce a paradigm shift in electronic systems design similar to that of the transition from vacuum tubes to semiconductor devices. Since low dimensional (1D and 2D) nano-structured materials exhibit unprecedented electro-mechanical properties in a wide frequency range, including radio-frequencies (RF), microwave nano-electronics provides an enormous and yet widely undiscovered opportunity for the engineering community. Carbon nano-electronics is one of the main research routes of RF/microwave nano-electronics. In particular, graphene has shown proven results as an emblematic protagonist, and a real solution for a wide variety of microwave electronic devices and circuits. This paper introduces graphene properties in the microwave range, and presents a paradigm of novel graphene-based devices and applications in the microwave/RF frequency range
Nanoantennas Design for THz Communication: Material Selection and Performance Enhancement
In the development of terahertz (THz) communication systems, the nanoantenna
is the most significant component. Especially, the focus is to design highly
directive antennas, because it enhances the performance of the overall system
by compensating the large path loss at THz and thus improves the
signal-to-noise ratio. This paper presents suitable material for nanoantenna
design and the advancement in their performance for THz communications. Copper,
Graphene, and carbon nanotube materials are used as promising candidates for
nanoantenna design. The performance of nanoantennas is carried out by analyzing
the properties and behavior of the material at THz. Results show that the
Graphene nanoantenna provides better performance in terms of miniaturization,
directivity, and radiation efficiency. Further, the performance enhancement of
the nanoantenna at THz is studied by dynamically adjusting the surface
conductivity via the chemical potential of Graphene using the electric field
effect. The performance of the nanoantenna is enhanced in terms of high
miniaturization, high directivity, low reflection, frequency reconfiguration,
and stable impedance. The THz nanoantennas using Graphene have the potential to
be used for THz communication systems. In view of the smart THz wireless
environment; this paper finally presents a THz Hypersurface using Graphene
meta-atoms. The user-side Graphene nanoantennas and environment-side Graphene
Hypersurface can build a promising smart THz wireless environment
Characterization of multi-wall carbon nanotubes and their applications
PhDCarbon nanotubes (CNT) and their applications is a field which has attract a lot of interest in the past two decades. Since the first invention of CNTs in 1991, and in view of utilising nanoantennas, the focus in many laboratories around the world has shifted to trying to lengthen nanotubes longer from nanometers to few centimeters. Eventually this could lead to CNTs’ use in sub-millimeter, millimiter wave and microwave antenna applications.
In this thesis, fundamental properties of carbon nanotube films are investigated, and some applications such as the use of CNTs as absorbers or CNT doped liquid crystals are considered. The concept of frequency tunable patch antennas is also presented. Simulation and measurement results of the liquid crystal based antenna show that frequency tuning is possible, through the use of a liquid crystal cell as a substrate. Additionally, greater tuning can be achieved using liquid crystals with higher dielectric anisotropy at microwave frequencies. This can be achieved by using CNT doped liquid crystals.
As mentioned, microwave and terahertz measurements of vertically aligned carbon nanotube arrays placed on the top surface of a rectangular silicon substrate are presented. The S-parameters are calculated allowing the extraction of the complex permittivity, permeability and conductivity of the samples. Theoretical models are being introduced delineating the behaviour of the multi-walled nanotube (MWNT) samples. The material properties of this film provide useful data for potential microwave and terahertz applications such as absorbers.
Finally, finite-difference time-domain (FDTD) modelling of CNTs is introduced, verifying the measurements that have been performed, confirming that CNT arrays can be highly absorptive. A novel estimation of the permittivity and permeability of an individual carbon nanotube is presented and a periodic structure is simulated, under periodic boundary conditions, consisting of solid anisotropic cylinders. In addition, the optical properties of vertically aligned carbon nanotube (VACNT) arrays, when the periodicity is both within the sub-wavelength and wavelength
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regime are calculated. The effect of geometrical parameters of the tube such as length, diameter and inter-tube distance between two consecutive tubes are also examined
Low-Dimensional Materials for Disruptive Microwave Antennas Design
This chapter is devoted to a complete analysis of remarkable electromagnetic properties of nanomaterials suitable for antenna design miniaturization. After a review of state of the art mesoscopic scale modeling tools and characterization techniques in microwave domain, new approaches based on wideband material parameters identification (complex permittivity and conductivity) will be described from impedance equivalence formulation achievement by de-embedding techniques applicable in integrated technology or in free space. A focus on performances of 1D materials such as vertically aligned multi-wall carbon nanotube (VA-MWCNT) bundles, from theory to technology, will be presented as a disruptive demonstration for defense and civil applications as in radar systems
Nematic Liquid Crystal Carbon Nanotube Composite Materials for Designing RF Switching Devices
Radio frequency microelectromechanical systems (RF MEMS) devices are microdevices used to switch or modify signals from the RF to millimeter wave (mmWave) frequency range. Liquid crystals (LCs) are widely used as electro-optic modulators for display devices. An electric field-induced electrical conductivity modulation of pure LC media is quite low which makes it difficult to use for RF MEMS switching applications. Currently, RF MEMS devices are characterized as an excellent option between solid-state and electromechanical RF switches to provide high isolation, low insertion loss, low power usage, excellent return loss, and large frequency band. However, commercial usage is low due to their lower switching speed, reliability, and repeatability. This research presents an electrical conductivity enhancement through the use of carbon nanotube (CNT) doping of LCs to realize a high-performance RF LC-CNT switching device. This thesis presents simulations of an RF switch using a coplanar waveguide (CPW) with a LC-CNT composite called 4-Cyano-4’-pentylbiphenyl multi-walled nanotube (5CB-MWNT) that is suitable for RF applications. The electrical conductivity modulation and RF switch performance of the 5CB-MWNT composite is determined using Finite Element Analysis (FEA). The simulations will present data on the coplanar waveguide’s s-parameters at the input and output ports S11 and S21 to measure return and insertion loss respectively, two key parameters for determining any RF switch’s performance. Furthermore, this thesis presents applications for improving tunable phased antenna arrays using the LC-CNT composite to allow for beam steering with high-gain and directivity to provide a broad 3D scannable coverage of an area. Tunable antennas are an important characteristic for 5G applications to achieve an optimal telecommunication system to prevent overcrowding of antennas and reduce overall system costs. This research investigates various device geometries with 5CB-MWNT to realize the best performing RF device for RF applications and 5G telecommunication systems. This research presents return and insertion loss data for three waveguide device configurations: CPW, coplanar waveguide grounded (CPWG), and finite ground coplanar waveguide grounded (FG-CPWG). The best results are shown using the CPW configuration. The return loss for the LC-CNT device showed a 5 dB improvement from -7.5 dB to -12.5 dB when using the LC-CNT signal line device. The insertion loss for this configuration showed a much more consistent 0 to -0.3 dB insertion loss value with much less noise when using the LC-CNT device compared to the -0.3 to -1 dB insertion loss value with heavy noise when using the Au signal line device. For the other two configurations the return loss and insertion loss value stayed the same indicating there is no loss in performance when using the LC-CNT switching mechanism. This is ideal due to the benefits that the LC-CNT switching mechanism provides like device reliability and increased switching speeds
Использование метаматериалов для улучшения электрических характеристик антенных устройств: обзор
Монография посвящена обзору современных исследований в области улучшения электрических характеристик антенных устройств с помощью метаматериалов. Даны физические принципы работы метаматериалов в видимом, инфракрасном и сверхвысокочастотном диапазонах. Проанализирован круг антенных задач, на решение которых направлено использование материалов с отрицательным коэффициентом преломления. Рассмотрены вопросы построения частотно-селективных поверхностей на основе метаматериалов, радиопоглощающих покрытий, антенн с малым электрическим размером. Приведен обзор работ, связанных с технологиями создания наноантенн в видимом и инфракрасном диапазонах, основанных на современных достижениях наноплазмоники. Монография предназначена для научных работников и инженеров, занимающихся
разработкой и проектированием миниатюрных антенн и устройств обработки сигналов в сверхвысокочастотном диапазоне, а также специалистов по наноплазмонике. Также монография будет полезна для обучающихся по направлению «Радиотехника» бакалавриата и магистерских программ при изучении разделов дисциплин, связанных с электродинамикой, антеннами, устройствами сверхвысокой частоты, оптикоэлектроникой и наноэлектроникой
Advanced Carbon Fiber Composite Materials for Shielding and Antenna Applications
Due to the low weight, ease of fabrication, low cost, high stiffness, high thermal and electrical conductivity, advanced carbon fiber composite (CFC) material is one of the most desirable materials which have been considered recently in the aerospace, electronic, and infrastructure industry.
This thesis examines the use of CFC materials for electromagnetic field shielding and antenna applications. Using a suitable electromagnetic model of composite materials, we evaluate the shielding effectiveness (SE) and other EM properties of composites paying attention to antenna design. Analytical and simulation results are compared with experimental data. Two kinds of composite materials are investigated, namely reinforced continuous carbon-fiber (RCCF) composites and carbon nanotube (CNT) composites.
For analytical SE analysis of multilayer RCCF composites, the material shows anisotropic behavior along the direction of the fibers, and we employ the transmission matrix method in conjunction with the anisotropic properties of each layer. The shielding performance of composites is also experimentally investigated. In order to enhance the conductivity of an RCCF composite, a small volume fraction of multi-walled carbon nanotubes (MWCNTs) is added to the RCCF material. We investigate the SE of the proposed MWCNT “nanocomposite” over a wide frequency band up to 26.5 GHz. The effect of aspect ratio on shielding performance is addressed as well. The effective conductivity of the nanocomposites was determined over the frequency range of interest.
The use of RCCF and single-walled carbon nanotube (SWCNT) composite is investigated for building antennas, by replacing the metal with CFC. We use an RCCF composite to build resonant and wideband antennas. The effect of the conductivity tensor of RCCF composite on the antenna performance is addressed. We also study the performance of a microstrip patch antenna with the ground plane made of RCCF composite.
As one of the most highly-conductive composite materials, single wall carbon nanotube (SWCNT) buckypapers are used to build composite antennas. A new fabrication method is proposed to print arbitrarily-shaped full-composite SWCNT antenna on any type of substrate. Various types of SWCNT antennas are fabricated for different antenna applications, namely UHF-RFID, WLAN, UWB, and mm-wave applications. Good agreement is observed between simulation and experimental results for all the aforementioned composite antennas.
Using the spectral domain method, the Green’s function is obtained for an infinitesimal HED on a dielectric slab over a CFC ground plane. Due to the high conductivity, CFCs are modeled using a surface impedance. The expressions for the electric field components are derived. The numerical integration details particularly dealing with low-converged tail of the integrand for fields at the air-dielectric interface are addressed. Numerical results based on this method compare well with results based on a time-domain finite integration technique. The effect of conductivity and anisotropy of the composite ground plane on electric field is investigated
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