Christopher W. Trueman

Compact Multiband Planar Antenna for 2.4/3.5/5.2/5.8-GHz Wireless Applications

A low-profile planar monopole antenna is proposed to operate within WLAN and WiMAX frequency bands. The antenna is composed of three radiating elements together with an additional strip to control the antenna performance. An electromagnetic (EM) model of the proposed antenna is developed in CST Microwave Studio for numerical analysis and optimization. The principle of operation and parametric study on the antenna performance are provided. Two dual-band and triple-band antennas are fabricated, and experimental results are presented.

Efficient implementations of the Crank-Nicolson scheme for the finite-difference time-domain method

When a finite-difference time-domain (FDTD) method is constructed by applying the Crank-Nicolson (CN) scheme to discretize Maxwells equations, a huge sparse irreducible matrix results, which cannot be solved efficiently. This paper proposes a factorization-splitting scheme using two substeps to decompose the generalized CN matrix into two simple matrices with the terms not factored confined to one sub-step. Two unconditionally stable methods are developed: one has the same numerical dispersion relation as the alternating-direction implicit FDTD method, and the other has a much more isotropic numerical velocity. The limit on the time-step size to avoid numerical attenuation is investigated, and is shown to be below the Nyquist sampling rate. The intrinsic temporal numerical dispersion is discussed, which is the fundamental accuracy limit of the methods.

Analysis and numerical experiments on the numerical dispersion of two-dimensional ADI-FDTD

The numerical dispersion relations in the literature are inconsistent for the alternate-direction-implicit finite-difference time-domain (ADI-FDTD) method. By analysis of the amplification factors, the numerical dispersion relation is rederived and verified with numerical experiments, with good agreement. The inconsistency of the numerical dispersion relation is resolved. It is shown that ADI-FDTD has some fundamental limits. For a given time step size, there is a velocity error even for zero spatial mesh. For a given spatial mesh size, the mesh does not support a numerical wave at certain time step sizes. As the Nyquist sampling limit is approached, the velocity of the wave approaches zero. At about twice the Nyquist limit, the wave does not propagate. Hence, the Nyquist criterion should be respected in choosing the time step size.

Carbon Nanotube Composites for Wideband Millimeter-Wave Antenna Applications

In this paper, we explore using carbon nanotube (CNT) composite material for wideband millimeter-wave antenna applications. An accurate electromagnetic model of the composite antenna is developed using Microwave Studio for numerical analysis. Good agreement between computed and measured results is shown for both copper and CNT antennas, and their performance is compared. The CNT antenna shows stable gain and radiation patterns over the 24 to 34 GHz frequency range. The dispersion characteristics of the CNT antenna show its suitability for wideband communication systems. Using a quarter-wave matched T-junction as feed network, a two-element CNT antenna array is realized and the performance is compared with a copper antenna. The housing effect on the performance of the CNT antenna is shown to be much lower than for the copper antenna.

Full-Composite Fractal Antenna Using Carbon Nanotubes for Multiband Wireless Applications

In this letter, single-wall carbon nanotube (CNT) composite materials are explored for the design of multiband antennas. An accurate electromagnetic (EM) model of the modified Sierpinski fractal composite antenna is developed using Microwave Studio for numerical analysis. For antenna fabrication, we printed CNT on both sides of a substrate and then cut out the desired antenna pattern using a high-precision milling machine. The CNT material was hardened by resin infiltration in order to be processed on the milling machine. The CNT antenna shows satisfactory gain and radiation patterns for UHF-RFID (900 MHz), Bluetooth (2.4 GHz), and WLAN (5.5 GHz) applications. Good agreement between computed and measured results is observed.

Reinforced Continuous Carbon-Fiber Composites Using Multi-Wall Carbon Nanotubes for Wideband Antenna Applications

We explore using reinforced continuous carbon fiber (RCCF) composite for wideband antennas in wireless applications. We use composite material as the radiating element for a wireless applications. An electromagnetic (EM) model of the composite antenna is developed using Microwave Studio for numerical analysis. An RCCF composite sample is prepared including up to 2% multiwall carbon nanotube (MWCNT) to enhance the conductivity. The anisotropic conductivity of the resulting material is determined by measurement using standard waveguide setups. The reflection coefficient, radiation pattern and gain of the composite antenna are investigated. The frequency- and time-domain dispersions are found for the composite antenna to show its suitability for ultrawideband (UWB) communication systems. It is observed that RCCF/MWCNT composite is an effectively alternative to metal for the antenna structure.

Carbon-fiber composite T-match folded bow-tie antenna for RFID applications

In this paper, we explore using advanced carbon-fiber composites in RFID antenna systems. For this purpose, the T-match folded bow-tie RFID antenna is considered for study and two different kinds of composites, braided-tissue of carbon-fibers and reinforced long carbon-fiber composites, are used as a material for the radiating element. Since braided-tissue of carbon-fiber composite shows isotropic behavior, the composite antenna has almost the same resonant frequency of 950 MHz as the metal antenna. However, the radiation efficiency degrades due to the low conductivity of composites compared to metals. By using anisotropic reinforced carbon-fiber composite as a material for the radiating element, the behavior of the antenna changes and the resonant frequency increases to 2.45 GHz. The anisotropic conductivity allows the antenna designer to largely restrict current flow to one direction, and this may lead to novel antenna designs.

Fields of complex surfaces using wire grid modelling

In the resonance range of frequencies, the scattered field from a complex surface such as a ship or aircraft depends on the geometry of the scatterer as a whole rather than on individual scattering centers. Excellent results are obtained by replacing the complex surface with an equivalent grid of wires or wire grid model. The calculation of the currents flowing on the wires of a grid by a moment method solution of an electric field integral equation is summarized. Assumptions made in the formulation lead to modelling guidelines which are local restrictions to the geometry of the wires of the grid. A set of wire grid guidelines or principles to aid in the global design of wire grid models is presented. The objective is an orthogonal grid of square cells of uniform side length. The wire grid guidelines provide a basis for compromise in grid design. They help identify weaknesses in wire grids. These principles are applied to model an ellipsoid and a sphere, with good agreement with measured data, and the exact solution, respectively. >

Multiwall Carbon Nanotube–Epoxy Composites With High Shielding Effectiveness for Aeronautic Applications

Using mass-produced multiwall carbon nanotubes (MWCNTs) from different providers, we have fabricated nanocomposites with high and nearly constant shielding effectiveness (SE) over a wide frequency range up to 26.5 GHz. The MWCNT weight fraction and sample thickness were lower than 10% and 2 mm, respectively. The fabrication process and percolation curves are described. A high dc conductivity of 239.1 S/m was achieved at an MWCNT loading of only 8% by weight. The effect of aspect ratio on shielding performance is addressed. By comparing the measured SE of the composite with predictions from a model of the measurement setup using Microwave Studio, the effective conductivity of the nanocomposite was determined. Since the thickness is very important for shielding analysis, the SE/unit thickness diagram was calculated by using the effective parameters of samples. The results were verified experimentally by measuring the SE of samples with different thicknesses.

An electromagnetics course with EMC applications for computer engineering students

When computer engineering students follow a different (separate) program of study from the electrical engineering students, only a single course in engineering electromagnetics can be accommodated in the computer engineering (CE) core program. An outline for a course on electromagnetics for computer engineering is given combining traditional electromagnetics topics with definitions, concepts, and discussions drawn from EMC. In this way engineering electromagnetics is made relevant and vital for the CE student. Specific EMC topics are included as they arise in a presentation based on a standard engineering electromagnetics text. Shielding, radiated emissions, susceptibility, the electromagnetic environment, EMC test methods, open sites, shielded anechoic rooms, screen rooms, TEM cells, and EMC test antennas are discussed. The goal of the computer engineering electromagnetics course is to prepare the student for a full-scale EMC course to be taken as an elective in the final undergraduate year or the first year of graduate study. >