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Electrical and Computer Engineering

Nader Engheta

Selected Works

2008

Articles 1 - 8 of 8

Full-Text Articles in Engineering

Achieving Transparency With Plasmonic And Metamaterial Coatings, Andrea Alù, Nader Engheta Jan 2008

Achieving Transparency With Plasmonic And Metamaterial Coatings, Andrea Alù, Nader Engheta

Nader Engheta

The possibility of using plasmonic and metamaterial covers to drastically reduce the total scattering cross section of spherical and cylindrical objects is discussed. While it is intuitively expected that increasing the physical size of an object may lead to an increase in its overall scattering cross section, here we see how a proper design of these lossless metamaterial covers near their plasma resonance may induce a dramatic drop in the scattering cross section, making these objects nearly “invisible” or “transparent” to an outside observer—a phenomenon with obvious applications for low-observability and noninvasive probe design. Physical insights into this phenomenon and …

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Guided Modes In A Waveguide Filled With A Pair Of Single-Negative (Sng), Double-Negative (Dng), And/Or Double-Positive (Dps) Layers, Andrea Alù, Nader Engheta Jan 2008

Guided Modes In A Waveguide Filled With A Pair Of Single-Negative (Sng), Double-Negative (Dng), And/Or Double-Positive (Dps) Layers, Andrea Alù, Nader Engheta

Nader Engheta

Here we present the results of our theoretical analysis for guided modes in parallel-plate waveguides filled with pairs of parallel layers made of any two of the following materials: 1) a material with negative real permittivity, but positive real permeability (epsilon-negative); 2) a material with negative real permeability, but positive real permittivity (mu-negative); 3) a material with both negative real permittivity and permeability (double-negative); and 4) a conventional material with both positive real permittivity and permeability (double-positive) in a given range of frequency. Salient properties of these guided modes are studied in terms of how these materials and their parameters …

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Electromagnetic Wave Propagation In The Wire Medium: A Complex Medium With Long Thin Inclusions, Charles Anthony Moses, Nader Engheta Jan 2008

Electromagnetic Wave Propagation In The Wire Medium: A Complex Medium With Long Thin Inclusions, Charles Anthony Moses, Nader Engheta

Nader Engheta

The wire medium is a type of complex artificial material we conceptually envision as many identical finite-length, parallel, thin wire inclusions embedded within a host medium. It is representative of a class of novel artificial materials characterized by long thin inclusions. Unlike some conventional artificial material, the inclusions of this class are not necessarily electrically short. Here, we present our theoretical analysis for wire media and by studying certain salient features of plane-wave propagation through these media, introduce equivalent medium parameters that depend, among other parameters, on the direction of wave propagation. The approach we use separates the artificial material …

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Theory And Simulations Of A Conformal Omni-Directional Sub-Wavelength Metamaterial Leaky-Wave Antenna, Andrea Alù, Filiberto Bilotti, Nader Engheta, Lucio Vegni Jan 2008

Theory And Simulations Of A Conformal Omni-Directional Sub-Wavelength Metamaterial Leaky-Wave Antenna, Andrea Alù, Filiberto Bilotti, Nader Engheta, Lucio Vegni

Nader Engheta

The detailed theory of a single subwavelength conformal radiator that exploits the resonant properties of thin cylindrical metamaterial shells supporting leaky waves is presented. It is shown and reviewed analytically and numerically how a circularly symmetric resonant leaky mode may be supported by a properly designed subwavelength homogenous cylindrical shell of low negative permittivity. Some physical insights are provided and numerical simulations with a feed point, considering also the finiteness of the antenna in the longitudinal direction, are presented and discussed. Moreover, possibilities and limitations of a practical realization of this setup are mentioned, considering in details the possible anisotropies …

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Radiation Characteristics Of Microstrip Dipole Antennas Over A High-Impedance Metamaterial Surface Made Of Hilbert Inclusions, John Mcvay, Ahmad Hoorfar, Nader Engheta Jan 2008

Radiation Characteristics Of Microstrip Dipole Antennas Over A High-Impedance Metamaterial Surface Made Of Hilbert Inclusions, John Mcvay, Ahmad Hoorfar, Nader Engheta

Nader Engheta

We analyze numerically the radiation characteristics of center-fed microstrip short dipoles and half-wave dipoles near a high-impedance surface made of Hilbert shape flat inclusions. We study the input impedance, pattern and gain of such radiating structures. We show that the radiation resistance of a microstrip dipole increases noticeably at certain frequencies near the resonant frequency of the Hilbert surface. Moreover, antenna gain enhancement at certain frequencies is observed for all dipole sizes we have analyzed.

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Far-Field Subdiffraction Optical Microscopy Using Metamaterial Crystals: Theory And Simulations, Alessandro Salandrino, Nader Engheta Jan 2008

Far-Field Subdiffraction Optical Microscopy Using Metamaterial Crystals: Theory And Simulations, Alessandro Salandrino, Nader Engheta

Nader Engheta

Here we suggest and explore theoretically an idea for a far-field scanless optical microscopy with a subdiffraction resolution. We exploit the special dispersion characteristics of an anisotropic metamaterial crystal that is obliquely cut at its output plane, or has a curved output surface, in order to map the input field distribution onto the crystal’s output surface with a compressed angular spectrum, resulting in a "magnified" image. This can provide a far-field imaging system with a resolution beyond the diffraction limits while no scanning is needed.

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Subwavelength, Compact, Resonant Patch Antennas Loaded With Metamaterials, Andrea Alù, Filiberto Bilotti, Nader Engheta, Lucio Vegni Jan 2008

Subwavelength, Compact, Resonant Patch Antennas Loaded With Metamaterials, Andrea Alù, Filiberto Bilotti, Nader Engheta, Lucio Vegni

Nader Engheta

We analyze the matching and radiation properties of subwavelength resonant patch antennas filled with double-negative, double-positive, and/or single-negative metamaterial blocks. Analyzing the theoretical limits inherently present when loading such common radiators with metamaterials, we show how these configurations may exhibit in principle an arbitrarily low resonant frequency for a fixed dimension, but they may not necessarily radiate efficiently when their size is electrically small. However, interesting possibilities are suggested to overcome these limitations by employing circular or more complex patch geometries in order to select specific modes that, when appropriate loading ratios between the filling materials are chosen, also ensure …

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Bandwidth, Cross-Polarization, And Feed-Point Characteristics Of Matched Hilbert Antennas, Jinhui Zhu, Ahmad Hoorfar, Nader Engheta Jan 2008

Bandwidth, Cross-Polarization, And Feed-Point Characteristics Of Matched Hilbert Antennas, Jinhui Zhu, Ahmad Hoorfar, Nader Engheta

Nader Engheta

In this work, we have applied a moment-method-based simulation code to perform a detailed parametric study of the bandwidth, cross-polarization level, and the feed location characteristics of the matched Hilbert antenna. It is shown that a properly chosen off-center near-the-end feed point may provide an approximate 50-Ω real input impedance at the fundamental resonant frequency. The role of different iteration order for Hilbert antennas, approximately matched to 50-Ω line, on the bandwidth and cross-polarization level of such antennas are investigated numerically. As was shown by Vinoy et al. the radiation patterns resemble those of a linear dipole and for a …

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