69,386 research outputs found
Metamaterials and the mathematical Science of invisibility
In this chapter, we review some recent developments in the field of
photonics: cloaking, whereby an object becomes invisible to an observer, and
mirages, whereby an object looks like another one (say, of a different shape).
Such optical illusions are made possible thanks to the advent of metamaterials,
which are new kinds of composites designed using the concept of
transformational optics. Theoretical concepts introduced here are illustrated
by finite element computations.Comment: This is a book chapter. 22 pages, 7 figure
Homogeneous optical cloak constructed with uniform layered structures
The prospect of rendering objects invisible has intrigued researchers for
centuries. Transformation optics based invisibility cloak design is now
bringing this goal from science fictions to reality and has already been
demonstrated experimentally in microwave and optical frequencies. However, the
majority of the invisibility cloaks reported so far have a spatially varying
refractive index which requires complicated design processes. Besides, the size
of the hidden object is usually small relative to that of the cloak device.
Here we report the experimental realization of a homogenous invisibility cloak
with a uniform silicon grating structure. The design strategy eliminates the
need for spatial variation of the material index, and in terms of size it
allows for a very large obstacle/cloak ratio. A broadband invisibility behavior
has been verified at near-infrared frequencies, opening up new oppotunities for
using uniform layered medium to realize invisibility at any frequency ranges,
where high-quality dielectrics are available
Metaphor. The good argument in science communication
The relation between metaphor and argumentation in science communication is becoming a crucial tool for critical metaphor studies. In this article, by means of a crossed analysis (epistemological, cognitive and linguistic), I focus especially on a peculiar dynamic of metaphor use in scientific communication showing opposite, paradoxical attitudes towards the use of metaphors, respectively, ubiquity vs. invisibility, inclination vs. resistance, deliberate vs. non-deliberate. In this way, an overall philosophical reflection about the underlying reasons for the ambivalence in the use of metaphor in scientific communication would be proposed and discussed
Cylindrical Invisibility Cloak with Simplified Material Parameters is Inherently Visible
It was proposed that perfect invisibility cloaks can be constructed for
hiding objects from electromagnetic illumination (Pendry et al., Science 312,
p. 1780). The cylindrical cloaks experimentally demonstrated (Schurig et al.,
Science 314, p. 997) and proposed (Cai et al., Nat. Photon. 1, p. 224) have
however simplified material parameters in order to facilitate easier
realization as well as to avoid infinities in optical constants. Here we show
that the cylindrical cloaks with simplified material parameters inherently
allow the zeroth-order cylindrical wave to pass through the cloak as if the
cloak is made of a homogeneous isotropic medium, and thus visible. To all
high-order cylindrical waves, our numerical simulation suggests that the
simplified cloak inherits some properties of the ideal cloak, but finite
scatterings exist.Comment: 10 pages, 3 figure
The science of difference : the invisibility of women in health sciences
Women remained invisible in health sciences until the late twentieth century because they were not included in the cohorts used in researched studies. Thanks to the work done by different groups of feminist researchers, we were able to visualise the need to change those paradigms. But while gender perspectives have allowed us to research new aspects of science, gender has sometimes contributed to rendering female-specific health issues as invisible. For women to be treated equally, their differences have to be recognised, precisely so that the equal right of both sexes to quality of life can be defended. Therefore, the science of difference should be included in research and taught in all health science specialisations
Non-Euclidean cloaking for light waves
Non-Euclidean geometry combined with transformation optics has recently led
to the proposal of an invisibility cloak that avoids optical singularities and
therefore can work, in principle, in a broad band of the spectrum [U. Leonhardt
and T. Tyc, Science 323, 110 (2009)]. Such a cloak is perfect in the limit of
geometrical optics, but not in wave optics. Here we analyze, both analytically
and numerically, full wave propagation in non-Euclidean cloaking. We show that
the cloaking device performs remarkably well even in a regime beyond
geometrical optics where the device is comparable in size with the wavelength.
In particular, the cloak is nearly perfect for a spectrum of frequencies that
are related to spherical harmonics. We also show that for increasing wavenumber
the device works increasingly better, approaching perfect behavior in the limit
of geometrical optics
Electromagnetic cloaking by layered structure of homogeneous isotropic materials
Electromagnetic invisibility cloak requires material with anisotropic
distribution of the constitutive parameters deduced from a geometrical
transformation as first proposed by Pendry et al. [Science 312, 1780 (2006)].
In this paper, we proposed a useful method to realize the required
radius-dependent, anisotropic material parameters and to construct an
electromagnetic cloak through concentric layered structure of thin, alternating
layers of homogeneous isotropic materials. With proper design of the
permittivity or the thickness ratio of the alternating layers, we demonstrated
the low-reflection and power-flow bending properties of the proposed cloaking
structure through rigorous analysis of the scattered electromagnetic fields.
The proposed cloaking structure does not require anisotropy or inhomogeneity of
the material constitutive parameters usually realized by metamaterials with
subwavelength structured inclusions, therefore may lead to a practical path to
an experimental demonstration of electromagnetic cloaking, especially in the
optical range.Comment: 9 pages, 5 figure
Invisibility and Cloaking: Origins, Present, and Future Perspectives
The development of metamaterials, i.e., artificially structured materials that interact with waves in unconventional ways, has revolutionized our ability to manipulate the propagation of electromagnetic waves and their interaction with matter. One of the most exciting applications of metamaterial science is related to the possibility of totally suppressing the scattering of an object using an invisibility cloak. Here, we review the available methods to make an object undetectable to electromagnetic waves, and we highlight the outstanding challenges that need to be addressed in order to obtain a fully functional coating capable of suppressing the total scattering of an object. Our outlook discusses how, while passive linear cloaks are fundamentally limited in terms of bandwidth of operation and overall scattering suppression, active and/or nonlinear cloaks hold the promise to overcome, at least partially, some of these limitations.AFOSR Award FA9550-13-1-0204NSF CAREER Award ECCS-0953311DTRA YIP Award HDTRA1-12-1-0022Electrical and Computer Engineerin
Macroscopic Invisibility Cloak for Visible Light
Invisibility cloaks, a subject that usually occurs in science fiction and
myths, have attracted wide interest recently because of their possible
realization. The biggest challenge to true invisibility is known to be the
cloaking of a macroscopic object in the broad range of wavelengths visible to
the human eye. Here we experimentally solve this problem by incorporating the
principle of transformation optics into a conventional optical lens fabrication
with low-cost materials and simple manufacturing techniques. A transparent
cloak made of two pieces of calcite is created. This cloak is able to conceal a
macroscopic object with a maximum height of 2 mm, larger than 3500
free-space-wavelength, inside a transparent liquid environment. Its working
bandwidth encompassing red, green and blue light is also demonstrated
Tension between visibility and invisibility: Science communication in new information environments
The visibility and invisibility of scientific knowledge, its creation, and of scientists are at the core of science communication research. Thus, prominent paradigms, such as the public understanding of science or public engagement with science and technology, have implications for the visibility of scientific knowledge in the scientific community and among the public. This article posits that visibility in science communication is achieved with the availability of scientific knowledge, the approval of its dissemination, and its accessibility to third parties. The public understanding of science and public engagement with science paradigms emphasize different aspects of visibility with the latter focusing on the visibility of the creation of scientific knowledge more than public understanding of science which focuses on the knowledge itself. The digital information environment has engendered new formats and possibilities for visibility but also new risks, thereby creating tensions in science communication
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