Engheta, Nader
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Publication Theory of simultaneous control of orientation and translational motion of nanorods using positive dielectrophoretic forces(2005-12-30) Edwards, Brian; Engheta, Nader; Evoy, StephaneThe manipulation of individual submicron-sized objects has been the focus of significant efforts over the last few years. A method to arbitrarily move and orient a set of rod-shaped conductive particles in a region defined by a set of electrodes using positive dielectrophoretic forces is presented. While the orientation of each particle is directly specified through the angle of the local electric field, its position is indirectly controlled through the applied force. Each electrode is approximated as an unknown point charge and an induced dipole. Since each induced dipole results from the combination of all other sources, a set of linear constraints are derived to enforce the self-consistency of the system. Additionally, the force and orientation of each particle also form an additional set of linear constraints. This combined set of constraints is then solved numerically to yield the sources required to induce the desired orientation and motion of each particle. It is observed that the minimum number of electrodes that can be used to control a set of N particles is 4N+1. Numerical simulations demonstrate that the control of a single nanorod (diameter of 70 nm; length of 1.4μm) in the midst of a realistic electrode array can be accomplished under practical conditions. In addition, such control of orientation and motion can be achieved over an ample region in the vicinity of each rod.Publication Theory and Simulations of a Conformal Omni-Directional Sub-Wavelength Metamaterial Leaky-Wave Antenna(2007-06-01) Alù, Andrea; Bilotti, Filiberto; Engheta, Nader; Vegni, LucioThe 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 in the metamaterials.Publication Theory of linear chains of metamaterial/plasmonic particles as subdiffraction optical nanotransmission lines(2006-11-15) Alù, Andrea; Engheta, NaderHere we discuss the theory and analyze in detail the guidance properties of linear arrays of metamaterial/ plasmonic small particles as nanoscale optical nanotransmission lines, including the effect of material loss. Under the assumption of dipolar approximation for each particle, which is shown to be accurate in the geometry of interest here, we develop closed-form analytical expressions for the eigenmodal dispersion in such arrays. With the material loss included, the conditions for minimal absorption and maximum bandwidth are derived analytically by studying the properties of such dispersion relations. Numerical examples with realistic materials, including their ohmic absorption and frequency dispersion, are presented. The analytical properties discussed here also provide some further physical insights into the mechanisms underlying the subdiffraction guidance in such arrays and their fundamental physical limits. The possibility of guiding beams with subwavelength lateral confinement and reasonably low decay is discussed, offering the possible use of this technique at microwave, infrared, and optical frequencies. Interpretation of these results in terms of nanocircuit concepts is presented, and possible extension to two- and three-dimensional nanotransmission line optical metamaterials is also foreseen.Publication Boosting Molecular Fluorescence with Plasmonic Nanolauncher(2009-07-21) Alù, Andrea; Engheta, NaderMolecular emission enhancement is generally obtained by proper coupling with external resonances. Here we propose the idea of a plasmonic nanolauncher, i.e., a metamaterial-inspired ultranarrow channel at cutoff. Its peculiar operation provides uniform phase and drastic amplitude increase all over the channel, allowing high emission enhancement independent of the position of an individual or group of molecules along the channel, and of its length and geometry. This may provide a fascinating mechanism for efficient molecular detection and enhanced optical fluorescence.Publication On the role of fractional calculus in electromagnetic theory(1997-08-01) Engheta, NaderWe have applied the concept of fractional derivatives/integrals in several specific electromagnetic problems, and have obtained promising results and ideas that demonstrate that these mathematical operators can be interesting and useful tools in electromagnetic theory. We give a brief review of the general principles, definitions, and several features of fractional derivatives/integrals, and then we review some of our ideas and findings in exploring potential applications of fractional calculus in some electromagnetic problems.Publication Peano High Impedance Surfaces(2005-12-01) McVay, John; Hoorfar, Ahmad; Engheta, NaderFollowing our previous work on metamaterial high-impedance surfaces made of Hilbert curve inclusions, here we theoretically explore the performance of the high-impedance surfaces made of another form of space-filling curve known as the Peano curve. This metamaterial surface, formed by a 2-D periodic arrangement of Peano curve inclusions, is located above a conducting ground plane and is shown to exhibit a high surface impedance surface at certain specific frequencies. Our numerical study reveals the effect of the iteration order of the Peano curve, the surface height above the conducting ground plane and the separation distance between adjacent inclusions.Publication Cloaking a Sensor(2009-06-08) Alù, Andrea; Engheta, NaderWe propose the general concept of cloaking a sensor without affecting its capability to receive, measure, and observe an incoming signal. This may be obtained by using a plasmonic sensor, based on cloaking, made of materials available in nature at infrared and optical frequencies, or realizable as a metamaterial at lower frequencies. The result is a sensing system that may receive and transmit information, while its presence is not perceived by the surrounding, which may be of fundamental importance in a wide range of biological, optics, physics, and engineering applications.Publication Phase and Amplitude of Fractional-Order Intermediate Wave(1999-06-05) Engheta, NaderThe behavior of the amplitude and phase of the "intermediate wave", which we previously introduced as certain fractional solutions to the standard scalar Helmholtz equation, is addressed and presented. These waves effectively behave as intermediate cases between the canonical cases of the plane-wave and cylindrical wave propagation. We show that the amplitude and phase of such intermediate wave undergo interesting "evolutions" as the fractionalization parameter ν attains fractional values between zero and unity. Possible extension into the novel concept of intermediate guided-wave geometries is just speculated.Publication Separation and contrast enhancement of overlapping cast shadow components using polarization(2006-08-01) Lin, Shih-Schön; Pugh, Edward N; Yemelyanov, Konstantin M; Engheta, NaderShadow is an inseparable aspect of all natural scenes. When there are multiple light sources or multiple reflections several different shadows may overlap at the same location and create complicated patterns. Shadows are a potentially good source of information about a scene if the shadow regions can be properly identified and segmented. However, shadow region identification and segmentation is a difficult task and improperly identified shadows often interfere with machine vision tasks like object recognition and tracking. We propose here a new shadow separation and contrast enhancement method based on the polarization of light. Polarization information of the scene captured by our polarization-sensitive camera is shown to separate shadows from different light sources effectively. Such shadow separation is almost impossible to realize with conventional, polarization-insensitive imaging.Publication Nonlocal Transformation Optics(2012-02-10) Castaldi, Giuseppe; Galdi, Vincenzo; Alù, Andrea; Engheta, NaderWe show that the powerful framework of transformation optics may be exploited for engineering the nonlocal response of artificial electromagnetic materials. Relying on the form-invariant properties of coordinate-transformed Maxwell’s equations in the spectral domain, we derive the general constitutive “blueprints” of transformation media yielding prescribed nonlocal field-manipulation effects and provide a physically incisive and powerful geometrical interpretation in terms of deformation of the equifrequency contours. In order to illustrate the potentials of our approach, we present an example of application to a wave-splitting refraction scenario, which may be implemented via a simple class of artificial materials. Our results provide a systematic and versatile framework which may open intriguing venues in dispersion engineering of artificial materials.