johac wrote:

Remember the old Star Trek series?

---


Engineers devise invisibility shield

Philip Ball

Electron effects could stop objects from scattering light.


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 Al 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.


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 Al 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. Al 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.

Al 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.



---
http://www.nature.com/news/2005/050228/full/050228-1.html

Philip Ball
http://news.google.com/news?q=%20%22Philip%20Ball%22&num=100&hl=en&lr=&ie=UTF-
8&oe=UTF-8&sa=N&tab=gn

http://www.google.com/search?q=%22Philip+Ball%22&num=100&hl=en&lr=&ie=UTF-8&oe
=UTF-8&tab=nw&sa=N

http://www.google.com/search?q=%22Philip+Ball%22&num=100&hl=en&lr=&output=sear
ch&cat=gwd/Top

http://groups.google.com/groups?as_epq=Philip%20Ball&safe=images&ie=UTF-8&oe=U
TF-8&as_scoring=d&lr=&num=100&hl=en

--
John Hachmann aa #1782

Intelligent Design has as much to do with science as reality
television has to do with reality. - Barry Lynn on CNN 12/25/04

johac wrote:

Remember the old Star Trek series?

---


Engineers devise invisibility shield

Philip Ball

Electron effects could stop objects from scattering light.


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 Al 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.


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 Al 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. Al 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.

Al 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.



---
http://www.nature.com/news/2005/050228/full/050228-1.html

Philip Ball
http://news.google.com/news?q=%20%22Philip%20Ball%22&num=100&hl=en&lr=&ie=UTF-8&oe=UTF-8&sa=N&tab=gn

http://www.google.com/search?q=%22Philip+Ball%22&num=100&hl=en&lr=&ie=UTF-8&oe=UTF-8&tab=nw&sa=N

http://www.google.com/search?q=%22Philip+Ball%22&num=100&hl=en&lr=&output=search&cat=gwd/Top

http://groups.google.com/groups?as_epq=Philip%20Ball&safe=images&ie=UTF-8&oe=UTF-8&as_scoring=d&lr=&num=100&hl=en

--
John Hachmann aa #1782

Intelligent Design has as much to do with science as reality
television has to do with reality. - Barry Lynn on CNN 12/25/04