625 research outputs found
Transformation media that rotate electromagnetic fields
We suggest a way to manipulate electromagnetic wave by introducing a rotation
mapping of coordinates that can be realized by a specific transformation of
permittivity and permeability of a shell surrounding an enclosed domain. Inside
the enclosed domain, the information from outside will appear as if it comes
from a different angle. Numerical simulations were performed to illustrate
these properties.Comment: 5 pages, 3 figure
Design and analytically full-wave validation of the invisibility cloaks, concentrators, and field rotators created with a general class of transformations
We investigate a general class of electromagnetic devices created with any
continuous transformation functions by rigorously calculating the analytical
expressions of the electromagnetic field in the whole space. Some interesting
phenomena associated with these transformation devices, including the
invisibility cloaks, concentrators, and field rotators, are discussed. By
carefully choosing the transformation function, we can realize cloaks which are
insensitive to perturbations at both the inner and outer boundaries.
Furthermore, we find that when the coating layer of the concentrator is
realized with left-handed materials, energy will circulate between the coating
and the core, and the energy transmits through the core of the concentrator can
be much bigger than that transmits through the concentrator. Therefore, such
concentrator is also a power flux amplifier. Finally, we propose a spherical
field rotator, which functions as not only a wave vector rotator, but also a
polarization rotator, depending on the orientations of the spherical rotator
with respect to the incident wave direction. The functionality of these novel
transformation devices are all successfully confirmed by our analytical full
wave method, which also provides an alternate computational efficient
validation method in contrast to numerical validation methods.Comment: 22 pages, 3 figure
A metamaterial frequency-selective super-absorber that has absorbing cross section significantly bigger than the geometric cross section
Using the idea of transformation optics, we propose a metamaterial device
that serves as a frequency-selective super-absorber, which consists of an
absorbing core material coated with a shell of isotropic double negative
metamaterial. For a fixed volume, the absorption cross section of the
super-absorber can be made arbitrarily large at one frequency. The double
negative shell serves to amplify the evanescent tail of the high order incident
cylindrical waves, which induces strong scattering and absorption. Our
conclusion is supported by both analytical Mie theory and numerical finite
element simulation. Interesting applications of such a device are discussed.Comment: 16 pages, 5 figure
LDEF Space Plasma-High Voltage Drainage Experiment post-flight results
The Space Plasma-High Voltage Drainage Experiment (SP-HVDE) was comprised of two identical experimental trays. With one tray located on the leading (ram facing, B10) edge and the other located on the trailing (wake facing, D4) edge of the Long Duration Exposure Facility (LDEF), it was possible to directly compare the effects of ram and wake spacecraft environments on charged dielectric materials. Six arrays of Kapton dielectric samples of 2 mil, 3 mil, and 5 mil thicknesses maintained at +/- 300, +/- 500, and +/- 1000 voltage bias formed the experimental matrix of each tray. In addition, each tray carried two solar cell strings, one biased at +300 volts and the other at -300 volts, to study current leakage from High Voltage Solar Arrays (HVSA). The SP-HVDE provides the first direct, long-term, in-flight measurements of average leakage current through dielectric materials under electric stress. The experiment also yields information on the long term stability of the bulk dielectric properties of such materials. Data and findings of the SP-HVDE are an extension of those from shorter term flight experiments such as the PIX-1 (Plasma Interaction Experiment) and PIX-2 and are therefore valuable in the design and evaluation of long-lived space systems with high voltage systems exposed to the low earth orbital environment. A summary of the SP-HVDE post flight analysis final report delivered to the LDEF Project Office under contract to the National Aeronautics and Space Administration is presented
Experimental Evaluation of Ultrasonic Simulation Techniques in Anisotropic Material
The high performance of the available computer technology provides the possibility to simulate the real life for ultrasonic inspections in terms of primary ultrasonic data like rf-time signals. For isotropic material codes like Generalized Point Source Synthesis (GPSS) or Elastodynamic Finite Integration Technique (EFIT) and the theoretical predictions correlate well with experimental results. Recently, the codes mentioned above have been extended to operate also in anisotropic material. In a first step the codes GPSS and EFIT have been expanded to work in materials of parallel oriented columnar grain structure with transversely isotropic symmetry. In order to verify these codes a set of experiments was carried out on weld metal pads and on welds of defined grain structure. Radiation, propagation, reflexion on boundaries and interaction of the sound field with defects for the modes “through transmission” and “pulse echo” were simulated and compared with the experiment
Time-of-flight imaging of invisibility cloaks
As invisibility cloaking has recently become experimental reality, it is
interesting to explore ways to reveal remaining imperfections. In essence, the
idea of most invisibility cloaks is to recover the optical path lengths without
an object (to be made invisible) by a suitable arrangement around that object.
Optical path length is proportional to the time of flight of a light ray or to
the optical phase accumulated by a light wave. Thus, time-of-flight images
provide a direct and intuitive tool for probing imperfections. Indeed, recent
phase-sensitive experiments on the carpet cloak have already made early steps
in this direction. In the macroscopic world, time-of-flight images could be
measured directly by light detection and ranging (LIDAR). Here, we show
calculated time-of-flight images of the conformal Gaussian carpet cloak, the
conformal grating cloak, the cylindrical free-space cloak, and of the invisible
sphere. All results are obtained by using a ray-velocity equation of motion
derived from Fermat's principle.Comment: 11 pages, 6 figures, journal pape
Ac magnetic susceptibility of a molecular magnet submonolayer directly patterned onto a microSQUID sensor
We report the controlled integration, via Dip Pen Nanolithography, of
monolayer dots of ferritin-based CoO nanoparticles (12 Bohr magnetons) into the
most sensitive areas of a microSQUID sensor. The nearly optimum flux coupling
between these nanomagnets and the microSQUID improves the achievable
sensitivity by a factor 100, enabling us to measure the linear susceptibility
of the molecular array down to very low temperatures (13 mK). This method opens
the possibility of applying ac susceptibility experiments to characterize
two-dimensional arrays of single molecule magnets within a wide range of
temperatures and frequencies.Comment: 4 pages 3 figure
Editorial
info:eu-repo/semantics/publishedVersio
Transformation bending device emulated by graded-index waveguide
We demonstrate that a transformation device can be emulated using a
gradient-index waveguide. The effective index of the waveguide is spatially
varied by tailoring a gradient thickness dielectric waveguide. Based on this
technology, we demonstrate a transformation device guiding visible light around
a sharp corner, with low scattering loss and reflection loss. The experimental
results are in good agreement with the numerical results.Comment: This paper is published at Optics Express 20, 13006 (2012
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