5,676 research outputs found
Spatially dispersive finite-difference time-domain analysis of sub-wavelength imaging by the wire medium slabs
In this paper, a spatially dispersive finite-difference time-domain (FDTD)
method to model wire media is developed and validated. Sub-wavelength imaging
properties of the finite wire medium slabs are examined. It is demonstrated
that the slab with its thickness equal to an integer number of half-wavelengths
is capable of transporting images with sub-wavelength resolution from one
interface of the slab to another. It is also shown that the operation of such
transmission devices is not sensitive to their transverse dimensions, which can
be made even comparable to the wavelength. In this case, the edge diffractions
are negligible and do not disturb the image formation.Comment: 14 pages, 13 figures, submitted to Optics Expres
Describing the set of words generated by interval exchange transformation
Let be an infinite word over finite alphabet . We get combinatorial
criteria of existence of interval exchange transformations that generate the
word W.Comment: 17 pages, this paper was submitted at scientific council of MSU,
date: September 21, 200
State-Selective High-Energy Excitation of Nuclei by Resonant Positron Annihilation
In the annihilation of a positron with a bound atomic electron, the virtual
gamma photon created may excite the atomic nucleus. We put forward this effect
as a spectroscopic tool for an energy-selective excitation of nuclear
transitions. This scheme can efficiently populate nuclear levels of arbitrary
multipolarities in the MeV regime, including monopole transitions and giant
resonances. In certain cases, it may have a higher cross sections than the
conventionally used Coulomb excitation
Subwavelength internal imaging by means of the wire medium
Evanescent wave amplification is observed, for the first time to our
knowledge, inside a half-wavelength-thick wire medium slab used for
subwavelength imaging. The wire medium is analyzed using both a spatially
dispersive finite-difference time-domain (FDTD) method and a full-wave
commercial electromagnetic simulator CST Microwave Studio. In this work we
demonstrate that subwavelength details of a source placed at a distance of
one-tenth of a wavelength from a wire medium slab can be detected inside the
slab with a resolution of approximately one-tenth of a wavelength in spite of
the fact that they cannot be resolved at the front interface of the device, due
to the rapid decay of evanescent spatial harmonics in free space
Homogenization of nonlocal wire metamaterial via a renormalization approach
It is well known that defining a local refractive index for a metamaterial
requires that the wavelength be large with respect to the scale of its
microscopic structure (generally the period). However, the converse does not
hold. There are simple structures, such as the infinite, perfectly conducting
wire medium, which remain non-local for arbitrarily large wavelength-to-period
ratios. In this work we extend these results to the more realistic and relevant
case of finite wire media with finite conductivity. In the quasi-static regime
the metamaterial is described by a non-local permittivity which is obtained
analytically using a two-scale renormalization approach. Its accuracy is tested
and confirmed numerically via full vector 3D finite element calculations.
Moreover, finite wire media exhibit large absorption with small reflection,
while their low fill factor allows considerable freedom to control other
characteristics of the metamaterial such as its mechanical, thermal or chemical
robustness.Comment: 8 pages on two columns, 7 figures, submitted to Phys. Rev.
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