1,097 research outputs found
Backward-wave regime and negative refraction in chiral composites
Possibilities to realize a negative refraction in chiral composites in in
dual-phase mixtures of chiral and dipole particles is studied. It is shown that
because of strong resonant interaction between chiral particles (helixes) and
dipoles, there is a stop band in the frequency area where the backward-wave
regime is expected. The negative refraction can occur near the resonant
frequency of chiral particles. Resonant chiral composites may offer a root to
realization of negative-refraction effect and superlenses in the optical
region
Near-field enhancement and sub-wavelength imaging in the optical region using a pair of two-dimensional arrays of metal nanospheres
Near-field enhancement and sub-wavelength imaging properties of a system
comprising a coupled pair of two-dimensional arrays of resonant nanospheres are
studied. The concept of using two coupled material sheets possessing surface
mode resonances for evanescent field enhancement is already well established in
the microwave region. This paper shows that the same principles can be applied
also in the optical region, where the performance of the resonant sheets can be
realized with the use of metallic nanoparticles. In this paper we present
design of such structures and study the electric field distributions in the
image plane of such superlens.Comment: 15 pages, 9 figure
Arbitrary beam control using passive lossless metasurfaces enabled by orthogonally-polarized custom surface waves
For passive, lossless impenetrable metasurfaces, a design technique for
arbitrary beam control of receiving, guiding, and launching is presented.
Arbitrary control is enabled by a custom surface wave in an orthogonal
polarization such that its addition to the incident (input) and the desired
scattered (output) fields is supported by a reactive surface impedance
everywhere on the reflecting surface. Such a custom surface wave (SW) takes the
form of an evanescent wave propagating along the surface with a spatially
varying envelope. A growing SW appears when an illuminating beam is received.
The SW amplitude stays constant when power is guided along the surface. The
amplitude diminishes as a propagating wave (PW) is launched from the surface as
a leaky wave. The resulting reactive tensor impedance profile may be realized
as an array of anisotropic metallic resonators printed on a grounded dielectric
substrate. Illustrative design examples of a Gaussian beam
translator-reflector, a probe-fed beam launcher, and a near-field focusing lens
are provided
Circularly Polarized Receiving Antenna Incorporating Two Helices to Achieve Low Backscattering
We propose to use an antenna composed of two orthogonal helices as a
low-scattering sensor. The vector effective length is derived for the antenna
using the small dipole approximation for the helices. The antenna can transmit
and receive circular polarization in all directions with the Huygens' pattern.
We observe that the antenna geometry does not backscatter, regardless of the
polarization, when the incidence direction is normal to the plane of the
helices. Scattered fields, scattered axial ratio, and the scattering cross
section are presented. We show that the zero-backscattering property holds also
for the antenna when it is capable to receive all the available power with
conjugate loading. The approximate analytical model is validated with full-wave
simulations.Comment: 14 pages, 7 figures. Submitted to IEEE Trans. Antennas Propa
Isotropic Chiral Objects With Zero Backscattering
In this paper we study electrically small chiral objects with isotropic
response and zero backscattering. A bi-isotropic sphere is used as a simple
example and its zero-backscattering conditions are studied. A theoretical model
of an object composed of three orthogonal chiral particles made of conducting
wire is presented as an analog of the zero-backscattering bi-isotropic sphere.
A potential application of the object as a receiving antenna or a sensor with
the ability to receive power from an arbitrary direction without backscattering
is discussed.Comment: 8 pages, 1 figure, submitted to IEEE Trans. Antennas Propa
Competing ideologies of Russia's civil society
Many analysts and public opinion makers in the West conflate the notions of Russia’s non-systemic liberal opposition and the country’s civil society. Indeed, despite garnering the support of a minority of Russia’s population, non-systemic liberal opposition represents a well-organized civic group with a clearly articulated agenda and the ability to take action. Yet, does Russia’s civil society end there? A closer look at the country’s politics shows that Russia has a substantial conservative-traditionalist faction that has also developed agenda for action and formulated opinions. This group is anti-liberal rather than illiberal ideologically and pro-strong state/pro a geopolitically independent Russia rather than pro-Kremlin politically. The interaction between liberal and conservative civic groups represents the battle of meanings, ideas, and ethics, and ultimately determines the future trajectory of Russia’s evolution. Thus, the analysis of Russia’s civil society must represent a rather more nuanced picture than a mere study of the liberal non-systemic opposition. This article will examine the complexity of Russia’s civil society scene with reference to the interplay between the liberal opposition and conservative majority factions. The paper will argue that such complexity stems from ideological value pluralism that falls far beyond the boundaries of the liberal consensus, often skewing our understanding of political practice in Russia
Effective electric and magnetic properties of metasurfaces in transition from crystalline to amorphous state
In this paper we theoretically study electromagnetic reflection,
transmission, and scattering properties of periodic and random arrays of
particles which exhibit both electric-mode and magnetic-mode resonances. We
compare the properties of regular and random grids and explain recently
observed dramatic differences in resonance broadening in the electric and
magnetic modes of random arrays. We show that randomness in the particle
positioning influences equally on the scattering loss from both electric and
magnetic dipoles, however, the observed resonance broadening can be very
different depending on the absorption level in different modes as well as on
the average electrical distance between the particles. The theory is
illustrated by an example of a planar metasurface composed of cut-wire pairs.
We show that in this particular case at the magnetic resonance the array
response is almost not affected by positioning randomness due to lower
frequency and higher absorption losses in that mode. The developed model allows
predictions of behavior of random grids based on the knowledge of
polarizabilities of single inclusions.Comment: 13 pages, 5 figures, and submitted to PR
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