Engheta, Nader
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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 Theory and potentials of multi-layered plasmonic covers for multi-frequency cloaking(2008-11-27) Alù, Andrea; Engheta, NaderWe have recently suggested that suitably designed plasmonic layers may cloak a given object simultaneously at multiple frequencies (Alù and Engheta 2008 Phys. Rev. Lett. 100 113901). Here, we extend our theory and fully analyze this possibility, highlighting the potentials of this plasmonic cloaking technique and its fundamental limitations dictated by the passivity and causality of the materials involved. The cloaking mechanism relies on the scattering cancellation properties of plasmonic materials. By exploiting their inherent frequency dispersion, it is possible to reduce the 'visibility' of a given object by several orders of magnitude simultaneously at multiple frequencies, such that any of the particular layers composing the cloak is responsible for noticeable reduction of scattering at each frequency of operation.Publication Mono-Modal Waveguides Filled with a Pair of Parallel Epsilon-Negative (ENG) and Mu-Negative (MNG) Metamaterial Layers(2003-06-08) Alù, Andrea; Engheta, NaderHere we analyze guided wave propagation in a parallel-plate waveguide filled with a pair of parallel lossless slabs; one possessing negative real permittivity but positive real permeability, and the other with negative real permeability and positive real permittivity, in the range of frequency of interest. It is shown that such a waveguide can support only a single propagating mode, essentially independent of the total thickness of this structure. Furthermore, this waveguide can still possess a propagating mode even when its thickness is very small. Field distribution and dispersion relations in such a mono-modal waveguide are obtained and discussed with physical insights and intuitive description for the mathematical findings.Publication How Does Zero Forward-scattering in Magnetodielectric Nanoparticles Comply with the Optical Theorem?(2010-05-19) Alù, Andrea; Engheta, NaderA few decades ago, Kerker et al. [J. Opt. Soc. Am. 73, 765-767 (1983)] theoretically pointed out the interesting possibility of conceiving small magnetodielectric spheres that may provide zero scattering in the forward direction, despite significantly larger scattering in any other direction. Recent experimental and theoretical papers on the topic have further discussed this possibility in more realistic scenarios. Inspecting some of their analyses, it seems indeed possible to conceive nanoparticles characterized by a scattering pattern with a sharp minimum, although not zero, in the forward direction. From a theoretical standpoint, however, it is well known that the total scattered power from any object has to be proportional to a portion of the scattered field in the forward direction, implying that very small or zero forward scattering should be synonymous to even smaller or zero total scattering, regardless of the nature of the object and of its design. Using analytical theory and an accurate scattering formulation, we clarify the nature of this apparent paradox and the limitations of this anomalous phenomenon in terms of particle size. In this way, we shed some new light on theoretical and experimental papers on the topic, identifying relevant missteps in some of their physical interpretation, and considering the general possibility of verifying these effects. This discussion may also be relevant to some cloaking applications using exotic artificial materials.Publication Optical nanoswitch: an engineered plasmonic nanoparticle with extreme parameters and giant anisotropy(2009-01-20) Alù, Andrea; Engheta, NaderNaturally available optical materials are known to provide a wide variety of electric responses, spanning from positive to negative permittivity values. In contrast, owing to drastically modified conduction properties at the microscopic level, at such high frequencies magnetism and conductivity are very challenging to realize. This implies that extreme (high or low) values of permittivity, although highly desirable for a wide range of optical applications, are difficult to realize in practice. Here, we suggest the design of an engineered resonant nanoparticle composed of two conjoined hemispheres, whose optical response may be changed at will from an ideal electric conductor to an ideal magnetic conductor. Near the nanoparticle internal resonant frequency, we derive a closed-form solution that describes the electromagnetic response of this nanoparticle, showing how its light interaction may become dramatically dependent on the local field polarization, passing through all possible impedance values (from zero to infinity) by a simple mechanical or polarization rotation. Considering realistic frequency dispersion and loss in optical materials, we further show that these concepts may be applied to different geometries, with possibility for future experimental feasibility. We forecast various applications of this geometry as an optical nanoswitch, a novel nanocircuit element and as a building block for novel optical metamaterials.Publication Adaptive Polarization-Difference Imaging Algorithms for Through-the-Wall Microwave Imaging Scenarios(2005-07-03) Yemelyanov, Konstantin M; McVay, John A; Engheta, Nader; Hoorfar, AhmadThe preliminary results of application of Adaptive Polarization-Imaging Algorithm for Through-the-Wall Microwave Imaging problems are presented. Use of complete polarization information in the scattered field from the object together with the adaptation technique provides enhancement in detection of target movement.Publication Metamaterials with Negative Permittivity and Permeability: Background, Salient Features, and New Trends(2003-06-08) Engheta, NaderHere we first present a brief background and the history of complex media, in particular the materials with negative permittivity and permeability, and then we discuss some of the salient electromagnetic features of these metamaterials. This is followed by description of some of the ideas regarding potential future applications of these metamaterials in devices and components, along with physical remarks and intuitive justification.Publication Fabrication of a Dual-Tier Thin Film Micro Polarization Array(2007-04-16) Gruev, Viktor; Ortu, Alessandro; Van der Spiegel, Jan; Lazarus, Nathan; Engheta, NaderA thin film polarization filter has been patterned and etched using reactive ion etching (RIE) in order to create 8 by 8 microns square periodic structures. The micropolarization filters retain the original extinction ratios of the unpatterned thin film. The measured extinction ratios on the micropolarization filters are ~1000 in the blue and green visible spectrum and ~100 in the red spectrum. Various gas combinations for RIE have been explored in order to determine the right concentration mix of CF4 and O2 that gives optimum etching rate, in terms of speed and under-etching. Theoretical explanation for the optimum etching rate has also been presented. In addition, anisotropic etching with 1μm under cutting of a 10μm thick film has been achieved. Experimental results for the patterned structures under polarized light are presented. The array of micropolarizers will be deposited on top of a custom made CMOS imaging sensor in order to compute the first three Stokes parameters in real time.Publication Anomolous Properties of Scattering from Cavities Partially Loaded With Double-Negative or Single-Negative Materials(2005-01-01) Bilotti, Filiberto; Alù, Andrea; Engheta, Nader; Vegni, LucioIn this paper, the theoretical justification and the numerical verification of the anomalous scattering from cavities partially filled with metamaterials are presented. A hybrid numerical formulation based on the Finite Element Method (FEM) and on the Boundary Integral (BI) for the analysis of cavity backed structures with complex loading metamaterials is first presented. The proposed approach allows the analysis of cavities filled with materials described by tensorial linear constitutive relations, which may well describe artificial metamaterials synthesized with proper inclusions in a host dielectric. It is found that cavities loaded with pairs of metamaterial layers with "resonant" features possess unusual scattering properties, and with judicious selection of constitutive parameters for these materials the transparency effect or significant enhancement in the backscattering from such cavities are obtained. This may be considered as a first step towards the analysis of the scattering and radiating features of cavity-backed patch antennas and reflect-arrays in presence of multilayered metamaterial loads.Publication Multifrequency Optical Invisibility Cloak with Layered Plasmonic Shells(2008-03-21) Alù, Andrea; Engheta, NaderHere, we theoretically suggest the possibility of employing a multilayered plasmonic shell as a cloak for reducing the total scattering cross section of a particle, simultaneously at different frequencies in the optical domain. By exploiting the frequency dispersion of plasmonic materials and their inherent negative polarizability, it is shown, theoretically and with numerical simulations, how covering a dielectric or conducting object of a certain size with this multilayered cloak may reduce its "visibility" by several orders of magnitude simultaneously at multiple frequencies.Publication Parallel-chain Optical Transmission Line for a Low-loss Ultraconfined Light Beam(2009-09-08) Alù, Andrea; Belov, Pavel A.; Engheta, NaderLinear arrays of plasmonic nanoparticles have been suggested by various groups as optical waveguides. Here, inspired by the concept of optical nanocircuits, we show that it is possible to improve the performance of such waveguide chains by pairing two of them, forming a two-wire optical transmission line. We show that choosing the operation regime near the light line may greatly reduce the effect of material absorption and disorder, still allowing field confinement in between the paired chains. Application for low-loss optical interconnects and subwavelength imaging devices are envisioned.