Here's how to make an invisibility cloak


    Theoretical cloaking device could soon become reality (sort of)

By Alan Boyle
Science editor
MSNBC
Updated: 2:03 p.m. ET May 25, 2006

*Alan Boyle*
Science editor
------------------------------------------------------------------------

Researchers say they are rapidly closing in on new types of materials
that can throw a cloak of invisibility around objects, fulfilling a
fantasy that is as old as ancient myths and as young as "Star Trek" and
the Harry Potter novels.

Unlike those tales of fictional invisibility, the real-life technologies
usually have a catch. Nevertheless, limited forms of invisibility might
be available to the military sooner than you think.

"We're very confident that at radar frequencies, these materials can be
implemented on a time scale of 18 months or so," John Pendry of Imperial
College London told MSNBC.com.

Pendry's research team is one of two groups whose results were posted
Thursday on the journal Science's Web site
<http://www.sciencexpress.org/> in advance of print publication. The two
papers lay out different theoretical methods for creating invisibility,
not only for radar but potentially for optical wavelengths as well.

Still more teams are out there with ideas to make things invisible --
using methods ranging from superlenses
<http://www.guardian.co.uk/science/story/0,,1766219,00.html> that cancel
out the light from nearby objects to actual cloaks
<http://projects.star.t.u-tokyo.ac.jp/projects/MEDIA/xv/oc.html> onto
which video can be projected as a moving camouflage. The most exotic
technologies involve "metamaterials," blends of polymers and tiny coils
or wires that twist the paths of electromagnetic radiation.

"There are recipes for controlling metamaterials," explained University
of Pennsylvania electrical engineer Nader Engheta, who published his own
invisibility recipe </id/7047872/> last year. "Metamaterials are very
interesting products."

The latest research papers describe how metamaterial could be fabricated
to bend light in carefully curved paths around the object to be hidden,
so that an observer would see right through it -- or more accurately,
right around it -- to the other side.

"The cloak would act like you've opened up a hole in space," Duke
University's David Smith, one of Pendry's co-authors, explained in a
news release. "All light or other electromagnetic waves are swept around
the area, guided by the metamaterial to emerge on the other side as if
they had passed through an empty volume of space."

Pendry told MSNBC.com that the cloak wouldn't reflect any light, and
wouldn't cast a shadow either. "It would be like Peter Pan had lost his
shadow," he said, referring to the fictional character who had to have
his shadow stitched back on.

**Dreams come true, with a few catches**

Theoretically at least, the metamaterial could work like the helmet of
invisibility celebrated in Greek myth
<http://www.mythweb.com/encyc/entries/hermes.html>, or the cloaking
device
<http://www.startrek.com/startrek/view/library/technology/article/70048.html>
that hid Romulan and Klingon vessels in the "Star Trek" series, or the
invisibility cloak
<http://www.hp-lexicon.org/magic/devices/devices_a-g.html#cloak_invisibility>
that came in so handy for Harry Potter in J.K. Rowlings' novels.

"Fiction has predicted the course of science for some time. ... Maybe
these Harry Potter novels were ahead of their time," Pendry said,
half-jokingly.

Of course, there are some scientific catches that the tale-tellers never
had to worry about:

    * For a total invisibility effect, the waves passing closest to the
      cloaked object would have to be bent in such a way that they would
      appear to exceed relativity's light speed limit. Fortunately,
      there's a loophole
      <http://groups.msn.com/AlanBoylesCosmicLog/102003archive.msnw?action=get_message&mview=0&ID_Message=1117>
      in Albert Einstein's rules of the road that allows smooth pulses
      of light to undergo just such a phase shift.
    * The invisibility effect would work only for a specific range of
      wavelengths. "There is a price to be paid if you want a thin
      cloak, in that it operates only over a narrow range of
      frequencies," Pendry said.
    * The cloak could be made to cover a volume of any shape, but "you
      can't flap your cloak," Pendry said. Moving the material around
      would spoil the effect.
    * The tiny structures embedded in the metamaterial would have to be
      smaller than the wavelength of the electromagnetic rays you wanted
      to bend. That's a tall order for optical invisibility, because the
      structures would have to be on the scale of nanometers, or
      billionths of a meter. It's far easier to create radar
      invisibility, Pendry said: "You're talking millimeters" -- that is,
      thousandths of a meter.

The radar application is of great interest to military outfits such as
the Defense Advanced Research Projects Agency, which funded Pendry's
team. "Radar is a defense technology, and if you wish to hide from it,
this sort of cloak would be a good way of doing it," he said. Such a
technology would be "far superior to stealth," he said.

If optical cloaks could be designed, that would be of interest to the
military as well. "One obvious thing would be that you could construct a
hutch in which you could hide a tank, and the hutch would make it appear
as though the tank wasn't there. ... You could also think of weightier
things, like submarines or battleships, where you might want to put some
of this stuff," Pendry said.

**Civilian applications, too**

There'd be plenty of applications in the civilian world as well, even
for rudimentary cloaking devices. For example, you could create
receptacles to shield sensitive medical devices from disruption by MRI
scanners, or build cloaks to route cellphone signals around obstacles.
"You may wish to put a cloak over the refinery that is blocking your
view of the bay," Duke University's David Schurig, another of Pendry's
co-authors, was quoted as saying.

While Pendry's team proposed constructing all-over cloaking devices, the
other research paper published Thursday describes a simpler method that
would involve shaping the metamaterials into cylindrical cloaking
devices. The method could also work to block sound waves -- like the cone
of silence <http://en.wikipedia.org/wiki/Cone_of_Silence> on the "Get
Smart" TV show, but not as silly.

The catch here is that the invisibility effect would work only if you
were on the same plane as the hidden object. "You could look on top of
it, and look inside the cloak," said the paper's author, Ulf Leonhardt
of the University of St. Andrews in Scotland.

Leonhardt told MSNBC.com that "potentially a mixture of the two schemes
will lead to a practical design." He said the paper from Pendry's team
gave him some additional ideas to work with.

"I read it for the first time just last Friday, and I've come up already
with something new," he said.

© 2006 MSNBC Interactive

© 2006 MSNBC.com 

http://www.msnbc.msn.com/id/12961080/?GT1=8199