Samir M. El-Ghazaly

A Low-Profile Branched Monopole Laptop Reconfigurable Multiband Antenna for Wireless Applications

A reconfigurable low-profile branched monopole antenna has been developed. It can operate at six different frequency bands that are 800 MHz, 900 MHz, 1.7 GHz, 1.9 GHz, 2.4 GHz, and 5.2 GHz. The developed antenna is compact and has a low-profile structure with dimensions of 96 mm times 9 mm times 3 mm, which makes it optimum for the laptop implementation. The antenna comprises two branches that are reconfigurable and is printed on a 0.05 -mm-thick Kapton substrate. Each branch is a multiband structure. Embedded switches are used for reconfiguration and are strategically positioned next to the ground plane to simplify the implementation of direct current (dc) biasing.

Rigorous Characterization of Carbon Nanotube Complex Permittivity Over a Broadband of RF Frequencies

This study presents a comprehensive characterization of the frequency dependence of the effective complex permittivity of bundled carbon nanotubes (CNTs) considering different densities over a broadband of frequencies from 10 MHz to 50 GHz using only one measurement setup. The extraction technique is based on rigorous modeling of coaxial and circular discontinuities using a mode matching technique in conjunction with an inverse optimization method to map the simulated scattering parameters to those measured by a vector network analyzer. The dramatic values of complex permittivity obtained at low frequencies are physically explained by the percolation theory. The effective permittivity of a mixture of nanoparticles of alumina and CNTs versus frequency and packing density is studied to verify the previously obtained phenomenon.

Global Modeling of Active Terahertz Plasmonic Devices

In this study, a full wave numerical technique is employed to characterize the propagation properties of 2-D plasmons along two-dimensional electron gas (2DEG) layers of biased hetero-structures at terahertz frequencies. This method is based on a coupled solution of Maxwell and hydrodynamic transport equations. In this manner, a complete description of carrier-wave interactions inside the 2DEG layer is obtained. Particularly, this simulator is employed to investigate the 2-D plasmon variations initiated by the application of an external bias along the hetero-structure. Substantial changes in the plasmon characteristics such as wavelength and decay length are reported. It is also revealed that two symmetrical plasmonic modes along the unbiased 2DEG layer split into new asymmetrical ones after applying the bias voltage. The simulation has been performed in different structures to examine the effects of various electron densities and the presence of periodic metallic gratings on the plasmon properties. Moreover, the 2-D plasmon reflections from boundaries terminated by ohmic contacts are separately studied. This research demonstrates the potentials of the 2-D conductors in the design of novel active terahertz plasmonic devices as modulators and amplifiers while proposing a new approach for their modeling. The results of this simulation are verified independently with an analytical model.

Mode matching technique-based modeling of coaxial and circular waveguide discontinuities for material characterization purposes

In this paper, it is proposed to use a cylindrical cell for the characterization of dielectric material. The extraction of complex permittivity is based on inverse gradient approach where the full-wave simulation results are mapped to experimental data to extract the complex permittivity. As the operational frequency of radio frequency (RF)/microwave devices is increased, it becomes difficult to accurately model waveguide transitions using traditional methods based on meshing such as finite-element method (FEM) where mesh size is determined according to the wavelength. Moreover, these techniques usually require extensive computational resources. Mode matching technique (MMT) is the full-wave tool implemented in this current work. It is used to compute the generalized scattering matrices (GSMs) of the different discontinuities of test setup. These GSMs model precisely discontinuities as they include the effects of all higher-order modes propagating and evanescent. Simulation and experimental results are included to validate the proposed approach for the rigorous modeling of those discontinuities and hence the extraction of complex permittivity.

Engineered Carbon-Nanotubes-Based Composite Material for RF Applications

Electrical properties of nanocomposite materials are extracted to investigate the possibility to engineer novel material for microwave applications. A measurement setup is developed to characterize material in a powder form. The developed measurement technique is applied on nanoparticles of alumina, carbon nanotubes (CNTs), and composite mixture of carbon nanotubes and alumina. The effect of packing density on dielectric constant and loss tangent is thoroughly characterized experimentally. The obtained results show that the real part of effective permittivity may be considerably enhanced by increasing the percentage of conducting nanoparticles. In addition, it is possible to decrease the loss in a material by mixing low-loss dielectric nanoparticles powder in a lossy material.

Miniaturized carbon nanotube-based RF resonator

Carbon nanotubes exhibit high dielectric constants. They have potential for miniaturizing RF and microwave components. In this paper, this property is utilized to realize a miniaturized CNT-based RF resonator. The resonator structure is excited through a 50-Ω copper-based transmission line. The preliminary design is developed using a full-wave High Frequency Structure Simulator (HFSS). Experimentally-extracted frequency-dependent complex permittivities of CNTs are incorporated in HFSS. The measured and simulated results are in close agreement. A comparison with identical graphite-based resonator verifies the unique behavior of CNTs, and confirms their potential for miniaturizing RF components.

Carbon nanotube-based planar transmission lines

In this paper, we explore building planar transmission lines using carbon nanotube (CNT) networks. We are successful in building the transmission lines and verifying the feasibility of potential planar transmission lines where carbon nanotube networks replace the conventional metallic traces. The experimental realization and the two-port microwave measurements of the proposed transmission lines enable accurate extractions of the fundamental parameters showing percolation effects in CNT networks. The frequency-dependent phase velocity characteristics show dramatic reduction compared to the speed of light in vacuum. The large magnitude of extracted complex permittivity for CNT networks also exhibits its percolation performance.

Broadband characterization of carbon nanotube networks

In this paper, the complex permittivity of carbon nanotube networks is extracted over a broadband of frequencies using a non destructive, simple, and low-cost procedure. The structure holding the material under test is a hollow circular waveguide shorted at one end and connected through precision adapter to the 1.85 mm-50-Ω coaxial cable of performance network analyzer. In this testing configuration, discontinuities between different transmission lines are modeled based on the full-wave mode matching technique. In this modeling, all higher-order modes propagating and evanescent are considered in the computation which produces generalized scattering matrices (GSMs). A gradient-optimization method is used to solve the inverse problem and extract the complex permittivity of material under test from the measured magnitude and phase of reflection coefficient. The technique is general and requires only a small fraction of material under test which can be in liquid, pulverized or solid form.

Analytical modeling of THz wave propagation inside ungated two dimensional electron gas layers

Plasma wave propagation along an ungated two Dimensional Electron Gas (2DEG) layer of a hetrostructure is studied. It is shown that the wave can be useful in amplification of THz signals. An analytical solution of Maxwell and Hydrodynamic equations is presented. This method provides an insight into electromagnetic modes allowed to propagate along the 2DEG as electrons are in motion with constant average drift velocity. Besides, wave impedances of the modes are illustrated. Afterwards, a simple matching network design for input and output ports of the 2DEGs is developed.

Measurement of dielectric properties of carbon nanotube networks used to build planar transmission lines

In this paper, we explore building planar trans-mission line from carbon nanotube (CNT) networks. We are successful in fabricating the transmission line and verifying the feasibility of potential planar transmission lines where carbon nanotube networks replace the metallic lines. The experimental realization and the two-port microwave measurements enabled us to extract accurately the fundamental parameters of the proposed transmission line. The frequency-dependent phase velocity char-acteristics show clearly its dramatic reduction compared to speed of light in vacuum. The complex permittivity of CNT networks is also reported in our work.