WASHINGTON - Scientists are boldly going where only fiction has gone
before - to develop a Cloak of Invisibility. It isn't quite ready to hide a
Romulan space ship from Capt. James T. Kirk or to disguise Harry Potter, but it
is a significant start and could show the way to more sophisticated designs.
A photo of the "metamaterial" cloak, released to
Reuters on October 19, 2006, which deflects microwave beams so they flow
around a "hidden" object inside with little distortion, making it appear
almost as if nothing were there at all. U.S. and British scientists said
on Thursday they had found a way to hide an object from microwave
radiation in a first step toward making a what they hope will be an
invisibility cloak. [Reuters] |
In this
first successful experiment, researchers from the United States and England were
able to cloak a copper cylinder.
It's like a mirage, where heat causes the bending of light rays and cloaks
the road ahead behind an image of the sky.
"We have built an artificial mirage that can hide something from would-be
observers in any direction," said cloak designer David Schurig, a research
associate in Duke University's electrical and computer engineering department.
For their first attempt, the researchers designed a cloak that prevents
microwaves from detecting objects. Like light and radar waves, microwaves
usually bounce off objects, making them visible to instruments and creating a
shadow that can be detected.
Cloaking used special materials to deflect radar or light or other waves
around an object, like water flowing around a smooth rock in a stream. It
differs from stealth technology, which does not make an aircraft invisible but
reduces the cross-section available to radar, making it hard to track.
The new work points the way for an improved version that could hide people
and objects from visible light.
Conceptually, the chance of adapting the concept to visible light is good,
Schurig said in a telephone interview. But, he added, "From an engineering point
of view it is very challenging."
The cloaking of a cylinder from microwaves comes just five months after
Schurig and colleagues published their theory that it should be possible. Their
work is reported in a paper in Friday's issue of the journal Science.
"We did this work very quickly ... and that led to a cloak that is not
optimal," said co-author David R. Smith, also of Duke. "We know how to make a
much better one."
The first working cloak was in only two dimensions and did cast a small
shadow, Smith said. The next step is to go for three dimensions and to eliminate
any shadow.
Viewers can see things because objects scatter the light that strikes them,
reflecting some of it back to the eye.
"The cloak reduces both an object's reflection and its shadow, either of
which would enable its detection," Smith said.
The cloak is made of metamaterials, which are mixtures of metal and circuit
board materials such as ceramic, Teflon or fiber composite.
In an ideal situation, the cloak and the item it is hiding would be
invisible. An observer would see whatever is beyond them, with no evidence the
cloaked item exists.
"Since we do not have a perfect cloak at this point, there is some reflection
and some shadow, meaning that the background would still be visible just
darkened somewhat. ... We now just need to improve the performance of cloaking
structures."
In a very speculative application, he added, "one could imagine 'cloaking'
acoustic waves, so as to shield a region from vibration or seismic activity."
Natalia M. Litchinitser, a researcher at the University of Michigan
department of electrical engineering and computer science who was not part of
the research team, said the ideas raised by the work "represent a first step
toward the development of functional materials for a wide spectrum of civil and
military applications."
Joining Schurig and Smith in the project were researchers at Imperial College
in London and SensorMetrix, a materials and technology company in San Diego.
The research was supported by the Intelligence Community Postdoctoral
Research Fellowship Program and the United Kingdom Engineering and Physical
Sciences Research Council.
