Invisibility Shields Planned by Engineers

[R.A. Hettinga]

<http://news.nationalgeographic.com/news/2005/02/0228_050228_invisibility.html>

Invisibility Shields Planned by Engineers
James Owen in London
for National Geographic News
February 28, 2005

 In popular science fiction, the power of invisibility is readily apparent.
Star Trek fans, for example, know that the devious Romulans could make
their spaceships suddenly disappear.

 But is the idea really so implausible? Not according to new findings by
scientists who say they have come up with a way to create cloaking device.

 Electronic engineers at the University of Pennsylvania in Philadelphia are
researching a device they say could make objects "nearly invisible to an
observer." The contrivance works by preventing light from bouncing off the
surface of an object, causing the object to appear so small it all but
disappears.

 The concept was reported today by the science news Web site
news at nature.com. It says the proposed cloaking device would not require any
peripheral attachments (such as antennas or computer networks) and would
reduce visibility no matter what angle an object is viewed at.

 Sir John Pendry, a physicist at Imperial College, London, said the concept
potentially holds several important applications "in stealth technology and
camouflage."

 While types of invisibility shielding have been developed before, the
phenomenon described by Andrea Alz and Nader Engheta sounds like something
that might have been witnessed from the bridge of science fiction's
starship Enterprise.

 The concept is based on a "plasmonic cover," which is a means to prevent
light from scattering. (It is light bouncing off an object that makes it
visible to an observer).

 The cover would stop light from scattering by resonating at the same
frequency as the light striking it. If such a device could cope with
different wavelengths of electromagnetic radiation (including visible
light), in theory, the object would vanish into thin air.

 Plasmonic Covers

 Alz and Engheta investigated experimental plasmonic covers that
incorporated metals, such as gold and silver, to hide visible light.

 When light strikes a metallic material, waves of electrons, called
plasmons, are generated. The engineers found that when the frequency of the
light striking the material matched the frequency of the plasmons, the two
frequencies act to cancel each other out.

 Under such conditions, the metallic object scattered only negligible
amounts of light.

 The researchers' studies show that spherical and cylindrical objects
coated with plasmonic shielding material produce very little light
scattering. These objects, when hit by the right wavelength of light, were
seen to become so small that they were almost invisible.

 The study is supported by the U.S. Defense Advanced Research Projects
Agency, which researches and develops cutting edge military technology.

 Some experts note, however, that cloaking devices that could enable
military vehicles and aircraft, let alone spaceships, to become completely
invisible to the enemy are likely to remain elusive for the foreseeable
future.

 John Pendry, the Imperial College physicist, said that light-shielding
covers would have to be customized to match the properties of each and
every object they hide.

 It would be still more difficult to devise shields that could cope with
all wavelengths of the visible spectrum-from red to violet light-and not
just a single color.

 Types of invisibility shielding previously proposed by scientists depend
on advanced camouflage systems, rather than objects being made to look
undetectably tiny. Such systems involve light sensors that create a mirror
image of the background scene on the concealed object.

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R. A. Hettinga <mailto: rah at ibuc.com>
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