1,721,183 research outputs found
Effects of size and frequency dispersion in plasmonic cloaking
Full text linkThe 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
Full text linkWe 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
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
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Gap plasmon-based metasurfaces: fundamentals and applications
No full textWe present the exciting functionalities of gap surface plasmon-based metasurfaces for light manipulation in reflection due to the excitation of gap surface plasmon resonances allowing for efficient control of phase and amplitude of reflected light. We specifically demonstrate that such plasmonic metasurfaces can be utilized for efficient unidirectional polarization-controlled coupling of incident light to propagating surface plasmon polariton modes. Fabricated metasurfaces that operate at telecommunication wavelengths 1500-1600nm feature a maximum coupling efficiency of ~25% for either of two linear polarizations of incident light and surface plasmon directivity exceeding 100.<br/
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
- …
