Alù, Andrea
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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 Robustness in Design and Background Variations in Metamaterial/Plasmonic Cloaking(2008-05-17) Alù, Andrea; Engheta, NaderHere we discuss our recent numerical results concerning the robustness of the scattering cancellation effect produced by a plasmonic cloak with near-zero permittivity and correspondingly negative polarizability. Being based on an integral effect and on an intrinsically non-resonant phenomenon, we show how variations of the geometrical parameters of the design and changes in the background do not sensibly affect the invisibility properties of the plasmonic/metamaterial cloak. Design examples are presented and discussed in order to highlight this robustness and to provide some insights into this cloaking phenomenon, different from other cloaking techniques recently presented in the literature.Publication Coupling of optical lumped nanocircuit elements and effects of substrates(2007-10-17) Alù, Andrea; Engheta, Nader; Salandrino, AlessandroWe present here an analytical quasi-static circuit model for the coupling among small nanoparticles excited by an optical electric field in the framework of the optical lumped nanocircuit theory [N. Engheta, A. Salandrino, and A. Alù, Phys. Rev. Lett. 95, 095504 (2005)]. We derive how coupling effects may affect the corresponding nanocircuit model by adding lumped controlled sources that depend on the optical voltages applied on the coupled particles as coupled lumped elements. With the same technique, we may model the presence of a substrate located underneath the nanocircuit elements, relating its presence to the coupling with a properly modeled image nanoparticle. These results are of importance in the understanding and the design of complex optical nanocircuits at infrared and optical frequencies.Publication Input Impedance, Nanocircuit Loading, and Radiation Tuning of Optical Nanoantennas(2008-07-25) Alù, Andrea; Engheta, NaderHere we explore the radiation features of optical nanoantennas, analyzing the concepts of optical input impedance, optical radiation resistance, impedance matching, and loading of plasmonic nanodipoles. We discuss how the concept of antenna impedance may be applied to optical frequencies and how its quantity may be properly defined and evaluated. We exploit these concepts in the optimization of nanoantenna loading by optical nanocircuit elements, extending classic concepts of radio-frequency antenna theory to the visible regime for the proper design and matching of plasmonic nanoantennas.Publication Infrared and optical invisibility cloak with plasmonic implants based on scattering cancellation(2008-08-01) Alù, Andrea; Silveirinha, Mário G; Engheta, NaderIn recent works, we have suggested that plasmonic covers may provide an interesting cloaking effect, dramatically reducing the overall visibility and scattering of a given object. While materials with the required properties may be directly available in nature at some specific infrared or optical frequencies, this is not necessarily the case for any given design frequency of interest. Here we discuss how such plasmonic covers may be specifically designed as metamaterials at terahertz, infrared, and optical frequencies using naturally available metals. Using full-wave simulations, we demonstrate that the response of a cover formed by metallic plasmonic implants may be tailored at will so that at a given frequency, it possesses the plasmonic-type properties required for cloaking applications.Publication Dynamical theory of artificial optical magnetism produced by rings of plasmonic nanoparticles(2008-08-01) Alù, Andrea; Engheta, NaderWe present a detailed analytical theory for the plasmonic nanoring configuration first proposed by Alù et al. [Opt. Express 14, 1557 (2006)], which is shown to provide negative magnetic permeability and negative index of refraction at infrared and optical frequencies. We show analytically how the nanoring configuration may provide superior performance when compared to some other solutions for optical negative-index materials, offering a more "pure" magnetic response at these high frequencies, which is necessary for lowering the effects of radiation losses and absorption. Sensitivity to losses and the bandwidth of operation of this magnetic inclusion are also investigated in detail and compared with other available setups.Publication Cloaking mechanism with antiphase plasmonic satellites(2008-11-12) Alù, Andrea; Silveirinha, Mário G; Engheta, NaderIn this work we theoretically demonstrate the possibility of cloaking a given object by surrounding it with a finite collection of suitably dimensioned, discrete "antiphase" plasmonic scatterers. It is shown that the total scattering from the object may approximately be canceled by the currents induced on a finite number of the plasmonic "satellite" scatterers, effectively making the whole system invisible to an external observer. Unlike other approaches, the proposed solution allows one to cloak a given object in a noninvasive manner since the antiphase satellites, being finite in number, do not need to fully cover and be in direct contact with the cloaked object.Publication Pairing an Epsilon-Negative Slab With a Mu-Negative Slab: Resonance, Tunneling and Transparency(2003-10-01) Alù, Andrea; Engheta, NaderHere, we analyze the transverse-magnetic (TM) wave interaction with a pair of slabs, one being an epsilon-negative (ENG) layer in which the real part of permittivity is assumed to be negative while its permeability has positive real part, and the other being a mu-negative (MNG) layer that has the real part of its permeability negative but its permittivity has positive real part. Although wave interaction with each slab by itself has predictable features, we show that the juxtaposition and pairing of such ENG and MNG slabs may, under certain conditions, lead to some unusual features, such as resonance, complete tunneling, zero reflection and transparency. The field distributions inside and outside such paired slabs are analyzed, and the Poynting vector distributions in such structures are studied. Using equivalent transmission-line models, we obtain the conditions for the resonance, complete tunneling and transparency, and we justify and explain the field behavior in these resonant paired structures. Salient features of the tunneling conditions, such as the roles of material parameters, slab thicknesses, dissipation, and angle of incidence are discussed. The analogy and correspondence between the ENG-MNG pair and the pair of a slab of conventional material juxtaposed with a “double-negative” medium is also discussed. Finally, a conceptual idea for a potential application of such a “matched” lossless ENG-MNG pair in “ideal” image displacement and image reconstruction is proposed.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.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.