613 research outputs found
Spatial dispersion and energy in strong chiral medium
Since the discovery of backward-wave materials, people have tried to realize
strong chiral medium, which is traditionally thought impossible mainly for the
reason of energy and spatial dispersion. We compare the two most popular
descriptions of chiral medium. After analyzing several possible reasons for the
traditional restriction, we show that strong chirality parameter leads to
positive energy without any frequency-band limitation in the weak spatial
dispersion. Moreover, strong chirality does not result in a strong spatial
dispersion, which occurs only around the traditional limit point. For strong
spatial dispersion where higher-order terms of spatial dispersion need to be
considered, the energy conversation is also valid. Finally, we show that strong
chirality need to be realized from the conjugated type of spatial dispersion.Comment: 6 pages, 2 figure
Breaking the challenge of signal integrity using time-domain spoof surface plasmon polaritons
In modern integrated circuits and wireless communication systems/devices,
three key features need to be solved simultaneously to reach higher performance
and more compact size: signal integrity, interference suppression, and
miniaturization. However, the above-mentioned requests are almost contradictory
using the traditional techniques. To overcome this challenge, here we propose
time-domain spoof surface plasmon polaritons (SPPs) as the carrier of signals.
By designing a special plasmonic waveguide constructed by printing two narrow
corrugated metallic strips on the top and bottom surfaces of a dielectric
substrate with mirror symmetry, we show that spoof SPPs are supported from very
low frequency to the cutoff frequency with strong subwavelength effects, which
can be converted to the time-domain SPPs. When two such plasmonic waveguides
are tightly packed with deep-subwavelength separation, which commonly happens
in the integrated circuits and wireless communications due to limited space, we
demonstrate theoretically and experimentally that SPP signals on such two
plasmonic waveguides have better propagation performance and much less mutual
coupling than the conventional signals on two traditional microstrip lines with
the same size and separation. Hence the proposed method can achieve significant
interference suppression in very compact space, providing a potential solution
to break the challenge of signal integrity
Negative reflections of electromagnetic waves in chiral media
We investigate the reflection properties of electromagnetic/optical waves in
isotropic chiral media. When the chiral parameter is strong enough, we show
that an unusual \emph{negative reflection} occurs at the interface of the
chiral medium and a perfectly conducting plane, where the incident wave and one
of reflected eigenwaves lie in the same side of the boundary normal. Using such
a property, we further demonstrate that such a conducting plane can be used for
focusing in the strong chiral medium. The related equations under paraxial
optics approximation are deduced. In a special case of chiral medium, the
chiral nihility, one of the bi-reflections disappears and only single reflected
eigenwave exists, which goes exactly opposite to the incident wave. Hence the
incident and reflected electric fields will cancel each other to yield a zero
total electric field. In another word, any electromagnetic waves entering the
chiral nihility with perfectly conducting plane will disappear.Comment: 5 pages, 5 figure
Quasi-Perron-Frobenius property of a class of saddle point matrices
The saddle point matrices arising from many scientific computing fields have
block structure , where the sub-block is symmetric and positive definite, and
is symmetric and semi-nonnegative definite. In this article we report a
unobtrusive but potentially theoretically valuable conclusion that under some
conditions, especially when is a zero matrix, the spectral radius of
must be the maximum eigenvalue of . This characterization approximates to
the famous Perron-Frobenius property, and is called quasi-Perron-Frobenius
property in this paper. In numerical tests we observe the saddle point matrices
derived from some mixed finite element methods for computing the stationary
Stokes equation. The numerical results confirm the theoretical analysis, and
also indicate that the assumed condition to make the saddle point matrices
possess quasi-Perron-Frobenius property is only sufficient rather than
necessary
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