Post by turbosnail on Mar 2, 2005 17:31:36 GMT 8
Read about it on Star Trek newsgroup. Just thought you may be interested.
Newsgroups: alt.tv.star-trek.tos,alt.startrek
Subject: Scientists Working On "Cloaking Device"
Published online: 28 February 2005; | doi:10.1038/news050228-1
Engineers devise invisibility shield
Philip Ball
Electron effects could stop objects from scattering light.
© NASA
The idea of a cloak of invisibility that hides objects from view has
long been confined to the more improbable reaches of science fiction.
But electronic engineers have now come up with a way to make one.
Andrea Alù and Nader Engheta of the University of Pennsylvania in
Philadelphia say that a 'plasmonic cover' could render objects "nearly
invisible to an observer". Their idea remains just a proposal at this
stage, but it doesn't obviously violate any laws of physics.
"The concept is an interesting one, with several important potential
applications," says John Pendry, a physicist at Imperial College in
London, UK. "It could find uses in stealth technology and camouflage."
Cloak of many colours
Types of invisibility shielding have been developed before, but these
mostly use the chameleon principle: a screen is coloured to match its
background, so that the screened object is camouflaged.
The concept could find uses in stealth technology and camouflage.
John Pendry
Physicist, Imperial College, UK
For example, inventor Ray Alden in North Carolina has proposed a system
of light detectors and emitters that project a replica of the scene
appearing behind an object from its front surface. Researchers at the
University of Tokyo are working on a camouflage fabric that uses a
similar principle, in which the background scene is projected on to
light-reflecting beads in the material.
But the invisibility shield proposed by Alù and Engheta in a preprint on
arXiv1 is more ambitious than this. It is a self-contained structure
that would reduce visibility from all viewing angles. In that sense it
would be more like the shielding used by the Romulans in the Star Trek
episode "Balance of Terror" in 1966, which hid their spaceships at the
push of a button.
Scatter-brained
The key to the concept is to reduce light scattering. We see objects
because light bounces off them; if this scattering of light could be
prevented (and if the objects didn't absorb any light) they would become
invisible. Alù and Engheta's plasmonic screen suppresses scattering by
resonating in tune with the illuminating light.
Plasmons are waves of electron density, caused when the electrons on the
surface of a metallic material move in rhythm. The researchers say that
a shell of plasmonic material will scatter light negligibly if the
light's frequency is close to the resonant frequency of the plasmons.
The scattering from the shell effectively cancels out the scattering
from the object.
For visible-light shielding, says Engheta, nature has already provided
suitable plasmonic materials: silver and gold. To reduce the scattering
of longer-wavelength radiation such as microwaves, one could make the
shield from a 'metamaterial': a large-scale structure with unusual
electromagnetic properties, typically constructed from arrays of wire
loops and coils.
Alù and Engheta's calculations show that spherical or cylindrical
objects coated with such plasmonic shields do indeed produce very little
light scattering. It is as though, when lit by light of the right
wavelength, the objects become extremely small, so small that they
cannot be seen.
Size matters
Pendry warns, however, that the concept as it stands is "no magic
cloak", because it would have to be delicately tuned to suit each
different object it hides. Perhaps even more of a drawback, he points
out, is the fact that a particular shield only works for one specific
wavelength of light.
An object might be made invisible in red light, say, but not in
multiwavelength daylight.
And crucially, the effect only works when the wavelength of the light
being scattered is roughly the same size as the object. So shielding
from visible light would be possible only for microscopic objects;
larger ones could be hidden only to long-wavelength radiation such as
microwaves. This means that the technology could not be used to hide
people or vehicles from human vision.
But that need not undermine other potential uses, Engheta says. For
example, the effect could be useful for making antiglare materials.
Another possible use for plasmonic screening is microscopy, he adds.
Light microscopes could surpass their usual resolution limits by using
tiny probes to measure the light field very close to the object being
imaged. Such probes could be made 'invisible' so that they don't disturb
the imaging signal.
And of course the shielding would work fine for concealing large objects
such as spaceships from sensors or telescopes that used long-wavelength
radiation instead of visible light.
www.nature.com/news/2005/050228/full/050228-1.html
ABSTRACT
Achieving transparency with plasmonic coatings
Authors: Andrea Alu, Nader Engheta
Comments: 18 pages, 14 figures, submitted to Phys. Rev. E
Subj-class: Materials Science
The possibility of using plasmonic covers to drastically reduce the
total scattering cross section of spherical and cylindrical objects is
discussed. While it is intuitively expected that increasing the physical
size of an object may lead to an increase in its overall scattering
cross section, here we see how a proper design of these lossless
metamaterial covers near their plasma resonance may induce a dramatic
drop in the scattering cross section, making the object nearly invisible
to an observer, a phenomenon with obvious applications for low
observability and non invasive probe design. Physical insights into this
phenomenon and some numerical results are provided.
arxiv.org/abs/cond-mat/0502336
Newsgroups: alt.tv.star-trek.tos,alt.startrek
Subject: Scientists Working On "Cloaking Device"
Published online: 28 February 2005; | doi:10.1038/news050228-1
Engineers devise invisibility shield
Philip Ball
Electron effects could stop objects from scattering light.
© NASA
The idea of a cloak of invisibility that hides objects from view has
long been confined to the more improbable reaches of science fiction.
But electronic engineers have now come up with a way to make one.
Andrea Alù and Nader Engheta of the University of Pennsylvania in
Philadelphia say that a 'plasmonic cover' could render objects "nearly
invisible to an observer". Their idea remains just a proposal at this
stage, but it doesn't obviously violate any laws of physics.
"The concept is an interesting one, with several important potential
applications," says John Pendry, a physicist at Imperial College in
London, UK. "It could find uses in stealth technology and camouflage."
Cloak of many colours
Types of invisibility shielding have been developed before, but these
mostly use the chameleon principle: a screen is coloured to match its
background, so that the screened object is camouflaged.
The concept could find uses in stealth technology and camouflage.
John Pendry
Physicist, Imperial College, UK
For example, inventor Ray Alden in North Carolina has proposed a system
of light detectors and emitters that project a replica of the scene
appearing behind an object from its front surface. Researchers at the
University of Tokyo are working on a camouflage fabric that uses a
similar principle, in which the background scene is projected on to
light-reflecting beads in the material.
But the invisibility shield proposed by Alù and Engheta in a preprint on
arXiv1 is more ambitious than this. It is a self-contained structure
that would reduce visibility from all viewing angles. In that sense it
would be more like the shielding used by the Romulans in the Star Trek
episode "Balance of Terror" in 1966, which hid their spaceships at the
push of a button.
Scatter-brained
The key to the concept is to reduce light scattering. We see objects
because light bounces off them; if this scattering of light could be
prevented (and if the objects didn't absorb any light) they would become
invisible. Alù and Engheta's plasmonic screen suppresses scattering by
resonating in tune with the illuminating light.
Plasmons are waves of electron density, caused when the electrons on the
surface of a metallic material move in rhythm. The researchers say that
a shell of plasmonic material will scatter light negligibly if the
light's frequency is close to the resonant frequency of the plasmons.
The scattering from the shell effectively cancels out the scattering
from the object.
For visible-light shielding, says Engheta, nature has already provided
suitable plasmonic materials: silver and gold. To reduce the scattering
of longer-wavelength radiation such as microwaves, one could make the
shield from a 'metamaterial': a large-scale structure with unusual
electromagnetic properties, typically constructed from arrays of wire
loops and coils.
Alù and Engheta's calculations show that spherical or cylindrical
objects coated with such plasmonic shields do indeed produce very little
light scattering. It is as though, when lit by light of the right
wavelength, the objects become extremely small, so small that they
cannot be seen.
Size matters
Pendry warns, however, that the concept as it stands is "no magic
cloak", because it would have to be delicately tuned to suit each
different object it hides. Perhaps even more of a drawback, he points
out, is the fact that a particular shield only works for one specific
wavelength of light.
An object might be made invisible in red light, say, but not in
multiwavelength daylight.
And crucially, the effect only works when the wavelength of the light
being scattered is roughly the same size as the object. So shielding
from visible light would be possible only for microscopic objects;
larger ones could be hidden only to long-wavelength radiation such as
microwaves. This means that the technology could not be used to hide
people or vehicles from human vision.
But that need not undermine other potential uses, Engheta says. For
example, the effect could be useful for making antiglare materials.
Another possible use for plasmonic screening is microscopy, he adds.
Light microscopes could surpass their usual resolution limits by using
tiny probes to measure the light field very close to the object being
imaged. Such probes could be made 'invisible' so that they don't disturb
the imaging signal.
And of course the shielding would work fine for concealing large objects
such as spaceships from sensors or telescopes that used long-wavelength
radiation instead of visible light.
www.nature.com/news/2005/050228/full/050228-1.html
ABSTRACT
Achieving transparency with plasmonic coatings
Authors: Andrea Alu, Nader Engheta
Comments: 18 pages, 14 figures, submitted to Phys. Rev. E
Subj-class: Materials Science
The possibility of using plasmonic covers to drastically reduce the
total scattering cross section of spherical and cylindrical objects is
discussed. While it is intuitively expected that increasing the physical
size of an object may lead to an increase in its overall scattering
cross section, here we see how a proper design of these lossless
metamaterial covers near their plasma resonance may induce a dramatic
drop in the scattering cross section, making the object nearly invisible
to an observer, a phenomenon with obvious applications for low
observability and non invasive probe design. Physical insights into this
phenomenon and some numerical results are provided.
arxiv.org/abs/cond-mat/0502336