576 research outputs found
Effects of size and frequency dispersion in plasmonic cloaking
No full textThe plasmonic venue to realize invisibility and cloaking [A. Alù and N. Engheta, Phys. Rev. E 72, 016623 (2005)] is analyzed here in terms of its limitations and its frequency dispersion relative to the cloak size. Intrinsic limits due to causality and comparison with transformation-based cloaking techniques are discussed and analyzed. An interestingly simple low-dispersion cloak is also suggested for background materials with larger refractive index. These results may shed light on this scattering cancellation phenomenon, suggesting potential applications in scattering reduction and noninvasive probing
A Metamaterial Surface for Compact Cavity Resonators
No full textWe suggest an idea for miniaturization of cavities by utilizing a properly designed metamaterial thin surface inserted inside the cavities. This metamaterial surface is constituted by a thin dielectric slab on both sides of which “gangbuster” dipoles are printed. Inserting the thin slab inside a parallel-plate one-dimensional (1-D) cavity resonator has the effect of decreasing the resonant frequency. Placing the metamaterial slab at the center of a rectangular waveguide also lowers the cut-off frequency of the dominant mode of the waveguide. The corresponding dispersion curve exhibits a smooth transition from a fast-wave to a slow-wave regime and then asymptotically tends to the dispersion curve of the first TE surface-wave mode of the metamaterial slab. This suggests a natural way to conceive a 3-D compact cavity resonator by placing two perfectly electric conducting walls, a half of the wavelength of the slow-wave mode apart, inside the above rectangular waveguide. The analysis, performed by a circuit network theory and validated by a full-wave numerical analysis, provides simple formulas to predict the resonant frequency and the dispersion diagrams of these structures
Caratterizzazione di antenne su substrati non tradizionali ed analisi frattale, in collaborazione con il Prof. Nader Engheta dell'Università di Philadelphia, USA
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Omnidirectional Metamaterial Antennas Based on-Near-Zero Channel Matching
No full textWe present an analytical model and practical design tools to realize cylindrically-symmetric compact antennas based on the anomalous transmission properties of ε -near-zero (ENZ) ultranarrow radial channels. The flexibility and exotic propagation properties in ENZ metamaterial channels are exploited here to tune and match cylindrically-symmetric antennas, without the need of complex external matching networks, in order to realize exciting antenna designs in terms of size, complexity and efficiency. We first model a homogenized Drude dispersive ENZ metamaterial channel to feed a radial parallel-plate waveguide; next we suggest a practical realization of this channel by using radial fins; eventually, we apply the obtained design formulas to realize single- and multi-band cylindrical antennas with a wide tunability range. The designed antennas may operate in the ultra-high frequency (UHF) band and may be realistically tuned over a large bandwidth. We envision applications in frequency-hopping, multi-band, compact, omnidirectional antennas
A single inverse-designed photonic structure that performs parallel computing
No full textIn the search for improved computational capabilities, conventional microelectronic computers are facing various problems arising from the miniaturization and concentration of active electronics. Therefore, researchers have explored wave systems, such as photonic or quantum devices, for solving mathematical problems at higher speeds and larger capacities. However, previous devices have not fully exploited the linearity of the wave equation, which as we show here, allows for the simultaneous parallel solution of several independent mathematical problems within the same device. Here we demonstrate that a transmissive cavity filled with a judiciously tailored dielectric distribution and embedded in a multi-frequency feedback loop can calculate the solutions of a number of mathematical problems simultaneously. We design, build, and test a computing structure at microwave frequencies that solves two independent integral equations with any two arbitrary inputs and also provide numerical results for the calculation of the inverse of four 5 x 5 matrices
A review on the potential use of metamaterial layers for increasing the transmission through a single sub-wavelength aperture in a flat opaque screen
No full textRecently, we have presented an idea for using metamaterial layers to enhance the transmission through a sub-wavelength aperture in an opaque screen. Our work was inspired and motivated by the experiments performed in the past few years by several groups worldwide, in which they demonstrated a significant enhancement of optical transmission through a single sub-wavelength hole in a metallic screen when the aperture is surrounded by properly designed periodic corrugations. Oliner, Jackson and their co-workers have elegantly explained this effect in terms of the leaky-wave theory, revealing how this phenomenon may be enhanced by a judicious choice of corrugation periods. Two important features were shown to be essential in their theory: (1) the screen material must have a negative permittivity at the operating frequency, thus allowing presence of the surface plasmons on the screen; (2) the corrugation should have a certain periodicity to excite the leaky waves. Here we present a review of our recent theoretical results, which rely on a different setup: a homogeneous metamaterial slab is placed over a perfectly conducting flat screen with a small hole. In some recent works, we have shown theoretically how a proper choice of material parameters for the metamaterial cover may lead to an analogous enhancement of transmission through the hole. In this problem, the screen may be perfectly conducting, and unlike the cases studied by others, no corrugation or periodicity on this screen is needed here. The leaky wave at the surface of the metamaterial cover provides similar effects both in collecting power from an incident plane wave and directing it into the hole and in increasing the wave transmission in the broadside direction on the other side of the screen. In this chapter, an overview of this idea is given, and the interested reader is referred to the references with detailed information
Theory and potentials of multi-layered plasmonic covers for multi-frequency cloaking
No full textWe 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 \u27visibility\u27 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
Theory of supercoupling, squeezing wave energy, and field confinement in narrow channels and tight bends using ε near-zero metamaterials
No full textIn this work, we investigate the detailed theory of the supercoupling, anomalous tunneling effect, and field confinement originally identified by Silveirinha and Engheta [Phys. Rev. Lett. 97, 157403 (2006)], where we demonstrated the possibility of using materials with permittivity ε near zero to drastically improve the transmission of electromagnetic energy through a narrow irregular channel with very subwavelength transverse cross section. Here, we present additional physical insights, describe applications of the tunneling effect in relevant waveguide scenarios (e.g., the perfect or super waveguide coupling), and study the effect of metal losses in the metallic walls and the possibility of using near-zero epsilon materials to confine energy in a subwavelength cavity with gigantic field enhancement. In addition, we systematically study the propagation of electromagnetic waves through narrow channels filled with anisotropic near-zero ε materials. It is demonstrated that these materials may have interesting potentials, and that for some particular geometries, the reflectivity of the channel is independent of the specific dimensions or parameters of near-zero ε transition. We also describe several realistic metamaterial implementations of the studied problems, based on standard metallic waveguides, microstrip line configurations, and wire media
Parallel-plate metamaterials for cloaking structures
No full textIn this work, we assess theoretically the physical response of metamaterial composite structures that emulate the behavior of negative-permittivity materials in certain relevant setups. The metamaterials under analysis consist of metallic parallel-plate implants embedded in a dielectric host in a two-dimensional geometry. Simple design rules and formulas are presented, fully considering the effect and consequences of excitation of higher-order diffraction modes at the metamaterial-dielectric interface. Following the ideas of transparency and cloaking developed by us [Alù and Engheta, Phys. Rev. E 72, 016623 (2005)], we demonstrate, analytically and numerically, that it is possible in this way to design metamaterial cloaks that significantly reduce the total scattering cross section of a given two-dimensional dielectric obstacle in some frequency band. This effect, which may be realized in a feasible way, may find interesting applications in electromagnetic cloaking, total scattering cross section reduction, and noninvasive probing
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