1,265 research outputs found
Photorealistic ray tracing of free-space invisibility cloaks made of uniaxial dielectrics
The design rules of transformation optics generally lead to spatially
inhomogeneous and anisotropic impedance-matched magneto-dielectric material
distributions for, e.g., free-space invisibility cloaks. Recently, simplified
anisotropic non-magnetic free-space cloaks made of a locally uniaxial
dielectric material (calcite) have been realized experimentally. In a
two-dimensional setting and for in-plane polarized light propagating in this
plane, the cloaking performance can still be perfect for light rays. However,
for general views in three dimensions, various imperfections are expected. In
this paper, we study two different purely dielectric uniaxial cylindrical
free-space cloaks. For one, the optic axis is along the radial direction, for
the other one it is along the azimuthal direction. The azimuthal uniaxial cloak
has not been suggested previously to the best of our knowledge. We visualize
the cloaking performance of both by calculating photorealistic images rendered
by ray tracing. Following and complementing our previous ray-tracing work, we
use an equation of motion directly derived from Fermats principle. The rendered
images generally exhibit significant imperfections. This includes the obvious
fact that cloaking does not work at all for horizontal or for ordinary linear
polarization of light. Moreover, more subtle effects occur such as
viewing-angle-dependent aberrations. However, we still find amazingly good
cloaking performance for the purely dielectric azimuthal uniaxial cloak.Comment: 12 pages, 3 figures, journal pape
Conformal carpet and grating cloaks
We introduce a class of conformal versions of the previously introduced
quasi-conformal carpet cloak, and show how to construct such conformal cloaks
for different cloak shapes. Our method provides exact refractive-index profiles
in closed mathematical form for the usual carpet cloak as well as for other
shapes. By analyzing their asymptotic behavior, we find that the performance of
finite-size cloaks becomes much better for metal shapes with zero average
value, e.g., for gratings.Comment: added Ref. 12; added 2 figures; reformatte
Optical phase cloaking of 700-nm light waves in the far field by a three-dimensional carpet cloak
Transformation optics is a design tool that connects geometry of space and
propagation of light. Invisibility cloaking is a corresponding benchmark
example. Recent experiments at optical frequencies have demonstrated cloaking
for the light amplitude ("ray cloaking"). In this Letter, we demonstrate
far-field cloaking of the light phase ("wave cloaking") by interferometric
microscope-imaging experiments on the previously introduced three-dimensional
carpet cloak at 700-nm wavelength and for arbitrary polarization of light
Scattering problems in elastodynamics
In electromagnetism, acoustics, and quantum mechanics, scattering problems
can routinely be solved numerically by virtue of perfectly matched layers
(PMLs) at simulation domain boundaries. Unfortunately, the same has not been
possible for general elastodynamic wave problems in continuum mechanics. In
this paper, we introduce a corresponding scattered-field formulation for the
Navier equation. We derive PMLs based on complex-valued coordinate
transformations leading to Cosserat elasticity-tensor distributions not obeying
the minor symmetries. These layers are shown to work in two dimensions, for all
polarizations, and all directions. By adaptative choice of the decay length,
the deep subwavelength PMLs can be used all the way to the quasi-static regime.
As demanding examples, we study the effectiveness of cylindrical elastodynamic
cloaks of the Cosserat type and approximations thereof
Experiments on transformation thermodynamics: Molding the flow of heat
It has recently been shown theoretically that the time-dependent heat
conduction equation is form-invariant under curvilinear coordinate
transformations. Thus, in analogy to transformation optics, fictitious
transformed space can be mapped onto (meta-)materials with spatially
inhomogeneous and anisotropic heat-conductivity tensors in the laboratory
space. On this basis, we design, fabricate, and characterize a micro-structured
thermal cloak that molds the flow of heat around an object in a metal plate.
This allows for transient protection of the object from heating, while
maintaining the same downstream heat flow as without object and cloak.Comment: 10 pages, 4 figure
Hall-effect sign-inversion in a realizable 3D metamaterial
In 2009, Briane and Milton proved mathematically the existence of
three-dimensional isotropic metamaterials with a classical Hall coefficient
which is negative with respect to that of all of the metamaterial constituents.
Here, we significantly simplify their blueprint towards an architecture
composed of only a single constituent material in vacuum/air, which can be seen
as a special type of porosity. We show that the sign of the Hall voltage is
determined by a separation parameter between adjacent tori. This qualitative
behavior is robust even for only a small number of metamaterial unit cells. The
combination of simplification and robustness brings experimental verifications
of this striking sign-inversion into reach.Comment: 9 figures, 7 page
Phonon band structures of three-dimensional pentamode metamaterials
Three-dimensional pentamode metamaterials are artificial solids that
approximately behave like liquids, which have vanishing shear modulus.
Pentamodes have recently become experimental reality. Here, we calculate their
phonon band structures for various parameters. Consistent with static continuum
mechanics, we find that compression and shear waves exhibit phase velocities
that can realistically be different by more than one order of magnitude.
Interestingly, we also find frequency intervals with more than two octaves
bandwidth in which pure single-mode behavior is obtained. Herein, exclusively
compression waves exist due to a complete three-dimensional band gap for shear
waves and, hence, no coupling to shear modes is possible. Such single-mode
behavior might, e.g., be interesting for transformation-elastodynamics
architectures.Comment: 5 figure
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