403 research outputs found
Parameterizing Quasiperiodicity: Generalized Poisson Summation and Its Application to Modified-Fibonacci Antenna Arrays
The fairly recent discovery of "quasicrystals", whose X-ray diffraction
patterns reveal certain peculiar features which do not conform with spatial
periodicity, has motivated studies of the wave-dynamical implications of
"aperiodic order". Within the context of the radiation properties of antenna
arrays, an instructive novel (canonical) example of wave interactions with
quasiperiodic order is illustrated here for one-dimensional (1-D) array
configurations based on the "modified-Fibonacci" sequence, with utilization of
a two-scale generalization of the standard Poisson summation formula for
periodic arrays. This allows for a "quasi-Floquet" analytic parameterization of
the radiated field, which provides instructive insights into some of the basic
wave mechanisms associated with quasiperiodic order, highlighting similarities
and differences with the periodic case. Examples are shown for quasiperiodic
infinite and spatially-truncated arrays, with brief discussion of computational
issues and potential applications.Comment: 29 pages, 10 figures. To be published in IEEE Trans. Antennas
Propagat., vol. 53, No. 6, June 200
Radiation from elementary sources in a uniaxial wire medium
We investigate the radiation properties of two types of elementary sources
embedded in a uniaxial wire medium: a short dipole parallel to the wires and a
lumped voltage source connected across a gap in a generic metallic wire. It is
demonstrated that the radiation pattern of these elementary sources have quite
anomalous and unusual properties. Specifically, the radiation pattern of a
short vertical dipole resembles that of an isotropic radiator close to the
effective plasma frequency of the wire medium, whereas the radiation from the
lumped voltage generator is characterized by an infinite directivity and a
non-diffractive far-field distribution.Comment: 10 pages, 4 figure
Giant radiation heat transfer through the micron gaps
Near-field heat transfer between two closely spaced radiating media can
exceed in orders radiation through the interface of a single black body. This
effect is caused by exponentially decaying (evanescent) waves which form the
photon tunnel between two transparent boundaries. However, in the mid-infrared
range it holds when the gap between two media is as small as few tens of
nanometers. We propose a new paradigm of the radiation heat transfer which
makes possible the strong photon tunneling for micron thick gaps. For it the
air gap between two media should be modified, so that evanescent waves are
transformed inside it into propagating ones. This modification is achievable
using a metamaterial so that the direct thermal conductance through the
metamaterial is practically absent and the photovoltaic conversion of the
transferred heat is not altered by the metamaterial.Comment: 4 pages, 3 figure
Analytical Study of Sub-Wavelength Imaging by Uniaxial Epsilon-Near-Zero Metamaterial Slabs
We discuss the imaging properties of uniaxial epsilon-near-zero metamaterial
slabs with possibly tilted optical axis, analyzing their sub-wavelength
focusing properties as a function of the design parameters. We derive in closed
analytical form the associated two-dimensional Green's function in terms of
special cylindrical functions. For the near-field parameter ranges of interest,
we are also able to derive a small-argument approximation in terms of simpler
analytical functions. Our results, validated and calibrated against a full-wave
reference solution, expand the analytical tools available for
computationally-efficient and physically-incisive modeling and design of
metamaterial-based sub-wavelength imaging systems.Comment: 25 pages, 9 figures (modifications in the text; two figures and
several references added
Spontaneous radiation of a finite-size dipole emitter in hyperbolic media
We study the radiative decay rate and Purcell effect for a finite-size dipole
emitter placed in a homogeneous uniaxial medium. We demonstrate that the
radiative rate is strongly enhanced when the signs of the longitudinal and
transverse dielectric constants of the medium are opposite, and the
isofrequency contour has a hyperbolic shape. We reveal that the Purcell
enhancement factor remains finite even in the absence of losses, and it depends
on the emitter size.Comment: 6 pages, 3 figure
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