3,894 research outputs found
Design and measurements of an electrically small, broad bandwidth, non-Foster circuit-augmented protractor antenna
A broad bandwidth, electrically small, metamaterial-inspired protractor antenna was designed, fabricated and tested around 300 MHz. Its broad bandwidth property was achieved by augmenting the protractor-shaped near-field resonant parasitic (NFRP) element with a non-Foster circuit. The resulting active NFRP element provided the means to surpass the fundamental passive limits. The measurement results for this non-Foster protractor antenna showed more than a 10 times increase of the 10 dB fractional bandwidth (FBW 10dB) of the original passive version. The corresponding half-power bandwidth (BW 3dB) was more than 8.24 times the passive upper bound. © 2012 American Institute of Physics
A metamaterial-inspired, electrically small rectenna for high-efficiency, low power harvesting and scavenging at the global positioning system L1 frequency
An electrically small rectenna was designed and tested at the global positioning system (GPS) L1 frequency (1.5754 GHz). The metamaterial-inspired near-field resonant parasitic antenna size (ka ∼ 0.467) and its direct match to the input impedance of the rectifying circuit decreased the whole size of the rectenna (ka ∼ 0.611). The simulated and measured rectifying efficiencies were, respectively, 75.7 and 79.6% when the input power to the rectifying circuit was 0.0 dBm (1 mW). The highest rectifying efficiency, 84.7%, was achieved at the GPS L1 frequency for a 3.0 dBm input power. The simulated and measured results are in good agreement. © 2011 American Institute of Physics
FDTD analysis of the tunneling and growing exponential in a pair of epsilon-negative and mu-negative slabs
Pairing together material slabs with opposite signs for the real parts of
their constitutive parameters has been shown to lead to interesting and
unconventional properties that are not otherwise observable for single slabs.
One such case was demonstrated analytically for the conjugate (i.e.,
complementary) pairing of infinite planar slabs of epsilon-negative (ENG) and
mu-negative (MNG) media [A. Alu, and N. Engheta, IEEE Trans. Antennas Prop.,
51, 2558 (2003)]. There it was shown that when these two slabs are juxtaposed
and excited by an incident plane wave, resonance, complete tunneling, total
transparency and reconstruction of evanescent waves may occur in the
steady-state regime under a monochromatic excitation, even though each of the
two slabs by itself is essentially opaque to the incoming radiation. This may
lead to virtual imagers with sub-wavelength resolution and other anomalous
phenomena overcoming the physical limit of diffraction. Here we explore how a
transient sinusoidal signal that starts at t = 0 interacts with such an ENG-MNG
pair of finite size using an FDTD technique. Multiple reflections and
transmissions at each interface are shown to build up to the eventual steady
state response of the pair, and during this process one can observe how the
growing exponential phenomenon may actually occur inside this bilayer.Comment: 14 pages, 9 figures, submitted to Phys Rev
Negative effective permeability and left-handed materials at optical frequencies
We present here the design of nano-inclusions made of properly arranged
collections of plasmonic metallic nano-particles that may exhibit a resonant
magnetic dipole collective response in the visible domain. When such inclusions
are embedded in a host medium, they may provide metamaterials with negative
effective permeability at optical frequencies. We also show how the same
inclusions may provide resonant electric dipole response and, when combining
the two effects at the same frequencies, lefthanded materials with both
negative effective permittivity and permeability may be synthesized in the
optical domain with potential applications for imaging and nano-optics
applications.Comment: 11 pages, 6 figures; modified the format, added a figur
Perfect absorption and giant magnification with a thin metamaterial layer
It is shown that perfect absorption and giant amplification can be realized
when a wave impinges on a special metamaterial layer with zero real parts of
the permittivity and permeability. The imaginary parts of the permittivity and
permeability remain nonzero, corresponding to finite loss or gain. Perfect
absorption and giant magnification can still be achieved even if the thickness
of the metamaterial layer is arbitrarily thin and the absolute imaginary parts
of the permittivity and permeability are very small. The metamaterial layer
needs a total-reflection substrate for perfect absorption, while this is not
required for giant magnification.Comment: 15 pages, 4 figure
Amplification of evanescent waves in a lossy left-handed material slab
We carry out finite-difference time-domain (FDTD) simulations, with a
specially-designed boundary condition, on pure evanescent waves interacting
with a lossy left-handed material (LHM) slab. Our results provide the first
full-wave numerical evidence for the amplification of evanescent waves inside a
LHM slab of finite absorption. The amplification is due to the interactions
between the evanescent waves and the coupled surface polaritons at the two
surfaces of the LHM slab and the physical process can be described by a simple
model.Comment: 4 pages, 2 figure
Where Are Be/black-hole Binaries?
We apply the tidal truncation model proposed by Negueruela & Okazaki(2001) to
arbitrary Be/compact star binaries to study the truncation efficiency
dependance on the binary parameters. We find that the viscous decretion disks
around the Be stars could be truncated very effectively in narrow systems.
Combining this with the population synthesis results of Podsiadlowski,
Rappaport and Han (2003) that binary black holes are most likely to be born in
systems with orbital periods less than about 30 days, we suggest that most of
the Be/black-hole binaries may be transient systems with very long quiescent
states. This could explain the lack of observed Be/black-hole X-ray binaries.
We also discuss the evolution of the Be/black-hole binaries and their possible
observational features.Comment: 14 pages,3 figures, ApJ accepte
Shape resonances in nested diffraction gratings
The diffraction problem of a plane wave impinging on a grating formed by
nested cavities is solved by means of the modal method, for and
polarization modes. The cavities are formed by perfectly conducting sheets that
describe rectangular profiles. The electromagnetic response of the grating is
analyzed, paying particular attention to the generation of resonances within
the structure. The dependence of the resonances on the geometrical parameters
of the grating is studied, and results of far and near field are shown. The
results are checked and compared with those available in the literature for
certain limit cases.Comment: 18 pages, 8 figure
Self-induced charge currents in electromagnetic materials, photon effective rest mass and some related topics
The contribution of self-induced charge currents of metamaterial media to
photon effective rest mass is discussed in detail in the present paper. We
concern ourselves with two kinds of photon effective rest mass, i.e., the
frequency-dependent and frequency-independent effective rest mass. Based on
these two definitions, we calculate the photon effective rest mass in the
left-handed medium and the 2TDLM media, the latter of which is described by the
so-called two time derivative Lorentz material (2TDLM) model. Additionally, we
concentrate primarily on the torque, which is caused by the interaction between
self-induced charge currents in dilute plasma (e.g., the secondary cosmic rays)
and interstellar magnetic fields (ambient cosmic magnetic vector potentials),
acting on the torsion balance of the rotating torsion balance experiment.Comment: 11 pages, Late
Plane waves with negative phase velocity in Faraday chiral mediums
The propagation of plane waves in a Faraday chiral medium is investigated.
Conditions for the phase velocity to be directed opposite to the direction of
power flow are derived for propagation in an arbitrary direction; simplified
conditions which apply to propagation parallel to the distinguished axis are
also established. These negative phase-velocity conditions are explored
numerically using a representative Faraday chiral medium, arising from the
homogenization of an isotropic chiral medium and a magnetically biased ferrite.
It is demonstrated that the phase velocity may be directed opposite to power
flow, provided that the gyrotropic parameter of the ferrite component medium is
sufficiently large compared with the corresponding nongyrotropic permeability
parameters.Comment: accepted for publication in Phys. Rev.
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