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Electrical and Electronics
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H. Nedwill Ramsey Professor of Electrical & Systems Engineering
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Now showing 1 - 10 of 66
Publication Peculiar Radar Cross-Section Properties of Double-Negative and Single-Negative Metamaterials(2004-04-26) Alù, Andrea; Engheta, NaderHere, we give an overview of some of the results of our analysis of anomalous scattering phenomena for structures involving metamaterial layers, and we provide some physical insights and ideas for potential applications.Publication General Class of Metamaterial Transformation Slabs(2010-03-25) Gallina, Ilaria; Castaldi, Giuseppe; Galdi, Vincenzo; Alù, Andrea; Engheta, NaderIn this paper, we apply transformation-based optics to the derivation of a general class of transparent metamaterial slabs. By means of analytical and numerical full-wave studies, we explore their imagedisplacement/ formation capabilities, and establish intriguing connections with configurations already known in the literature. Starting from these revisitations, we develop a number of nontrivial extensions, and illustrate their possible applications to the design of perfect radomes, anticloaking devices, and focusing devices based on double-positive (possibly nonmagnetic) media. These designs show that such anomalous features may be achieved without necessarily relying on negative-index or strongly resonant metamaterials, suggesting more practical venues for the realization of these devices.Publication Enhanced Directivity From Subwavelength Infrared/Optical Nano-Antennas Loaded With Plasmonic Materials or Metamaterials(2007-11-01) Alù, Andrea; Engheta, NaderHere, we explore theoretically the concept of enhanced directivity from electrically small subwavelength radiators containing negative-parameter materials, such as plasmonic materials with negative permittivity at THz, infrared and optical frequencies. In particular, we study higher order plasmonic resonances of a subwavelength core-shell spherical nano-antenna, and we analyze the near-zone field distributions and far-field radiation patterns of such a structure when it is excited by a small dipole source, demonstrating analytically and numerically the possibility of having highly directive patterns from a nano-structure with electrically small dimensions. Radiation characteristics and intrinsic limitations on performance are analyzed in detail, and a potential application of this novel technique for super-resolution detection of the displacement of a nano-object is also pointed out.Publication Design of nanofilters for optical nanocircuits(2008-04-01) Alù, Andrea; Engheta, Nader; Young, Michael EWe theoretically and numerically study the design of optical "lumped" nanofiltering devices in the framework of our recently proposed paradigm for optical nanocircuits. In particular, we present a design of basic filtering elements, such as low-pass, pass-band, stop-band, and high-pass lumped nanofilters, for use in optical nanocircuits together with more complex designs, such as multizero or multipole nanofilters, to work at THz, infrared, and optical frequencies. Following the nanocircuit theory, we show how it is possible to design such complex frequency responses by applying simple rules, similar to those in rf circuit design, and we compare the frequency response of these optical nanofilters with classic filters in rf circuits. These findings introduce a theoretical foundation for the fabrication of nanofilters in optical lumped nanocircuit devices.Publication Peano Antennas(2004-01-01) Zhu, Jinhui; Hoorfar, Ahmad; Engheta, NaderIn this letter, we investigate the radiation characteristics of Peano antenna, i.e., a single antenna made of a thin wire, patterned after a special type of space-filling curve known as the Peano curve. We use a moment-method-based simulation code to study various properties of this antenna, namely, the radiation pattern, impedance bandwidth, current distribution, cross-polarization level, radiation efficiency, and the feed location for achieving an electrically small matched antenna. As in the case of the Hilbert antenna, the radiation patterns of a Peano antenna resemble those of a linear dipole; however, this antenna has a lower cross-polarization level than the Hilbert antenna and, for a matched Peano antenna, the resonant frequency is lower than the same order matched Hilbert antenna at the expense of a smaller input-impedance bandwidth.Publication Far-field subdiffraction optical microscopy using metamaterial crystals: Theory and simulations(2006-08-01) Salandrino, Alessandro; Engheta, NaderHere 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.Publication Plasmonic and Metamaterial Cloaking: Physical Mechanisms and Potentials(2008-09-01) Alù, Andrea; Engheta, NaderArtificial materials, metamaterials and plasmonic media have recently received tremendous attention from the scientific communities, media and general public, following novel ideas and suggestions for their potential use in a variety of applications such as cloaking. Here we briefly review and highlight some of the available solutions for invisibility and cloaking that employ metamaterials and plasmonic materials at various frequencies. We briefly overview some of the different cloaking mechanisms recently proposed in the literature, such as plasmonic cloaking based on scattering cancellation, coordinate-transformation cloaking and anomalous localized resonances for cloaking, in particular providing some details for scattering-cancellation-based plasmonic cloaking. We mention the main analogies and differences among these various approaches, and we discuss some possible ideas for realizations and applications of these results, with particular attention to the physical phenomena involved.Publication Shaping Light Beams in the Nanometer Scale: A Yagi-Uda Nanoantenna in the Optical Domain(2007-12-06) Salandrino, Alessandro; Li, Jingjing; Engheta, NaderAYagi-Uda-like optical nanoantenna concept using resonant core-shell plasmonic particles as its “reflectors” and “directors” is studied numerically. Such particles when placed near an optical dipole source in a certain arrangement may exhibit large induced dipole moments, resulting in shaping the far-field radiation pattern, analogous to the far field of classical Yagi-Uda antennas in the microwave regime. The variation of the ratio of radii in concentric core-shell nanostructure is used to tailor the phase of the polarizabilities of the particles and, consequently, the antenna’s far-field pattern. The idea of a nanospectrum analyzer is also briefly proposed for molecular spectroscopy.Publication Cloaked Near-Field Scanning Optical Microscope Tip for Noninvasive Near-Field Imaging(2010-12-29) Alù, Andrea; Engheta, NaderNear-field imaging is a well-established technique in biomedical measurements, since closer to the detail of interest it is possible to resolve subwavelength details otherwise unresolved by regular lenses. A near-field scanning optical microscope (NSOM) tip may indeed overcome the resolution limits of far-field optics, but its proximity inherently perturbs the measurement. Here, we apply the recent concept of a ‘‘cloaked sensor’’ to an NSOM device in collection mode, showing theoretically how a proper plasmonic cover applied to an NSOM tip may drastically improve its overall measurement capabilities.Publication Sub-wavelength Focusing and Negative Refraction along Positive-Index and Negative-Index Plasmonic Nano-Transmission Lines and Nano-Layers(2005-07-03) Alù, Andrea; Engheta, NaderFollowing our recent works on the concept of plasmonic nano-inductors and nano-capacitors and related complex circuits, here we analyze the possibility of designing nano-transmission-lines (NTL) made of these basic nano-elements. We show that in the limit in which these basic circuit elements are very close to each other, they can be regarded as planar stacks of plasmonic and nonplasmonic slabs, which may be designed to act as forward (right-handed) or backward (lefthanded) NTL. Negative refraction and left-handed propagation are shown to be possible in these planar plasmonic configurations, potentially applicable in several innovative setups for subwavelength focusing, imaging and waveguiding applications.