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New Theory: How to Make Objects Invisible

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  • Amy Harlib
    aharlib@earthlink.net Fascinating! http://www.livescience.com/technology/050228_invisible_shield.html
    Message 1 of 1 , Mar 2, 2005
      > New Theory: How to Make Objects Invisible
      > By Robert Roy Britt
      > LiveScience Senior Writer
      > posted: 28 February 2005
      > High-tech cloaking machines could one day render very small objects nearly
      > invisible and perhaps improve military stealth technology, scientists said
      > Monday.
      > The idea is straight out of science fiction - cloaking technology made
      > Romulan spaceships disappear in Star Trek. A humble version of the device
      > could become a reality, according to Nader Engheta and Andrea Alu of the
      > University of Pennsylvania.
      > But don't expect to hide yourself or your spaceship anytime soon, at least
      > not in the standard sense of invisible. In practical terms, the research
      > is more likely to lead to improved technical and research devices, and
      > even these applications are years away.
      > How it would work
      > The proposal involves using plasmons - tiny electronic excitations on the
      > surfaces of some metals - to cancel out the visible light or other
      > radiation coming from an object.
      > "A proper design . may induce a dramatic drop in the scattering
      > cross-section, making the object nearly invisible to an observer," Nader
      > and Alu write in a scientific paper
      > [http://arxiv.org/abs/cond-mat/0502336%5d that was made available to the
      > public Feb. 14.
      > But cloaking ability would depend on an object's size, so that only with
      > very small things - items that are already microscopic or nearly so -
      > could the visible light be rendered null. A human could be made impossible
      > to detect in longer-wavelength radiation such as microwaves, but not from
      > visible light.
      > A spaceship might be made transparent to radio waves or some other
      > long-wavelength detector.
      > The idea is in an infant stage but appears not to violate any laws of
      > physics, according to an article Monday in news@..., an online
      > companion to the journal Nature, which provided advance copies of the
      > story to reporters.
      > "The concept is an interesting one, with several important potential
      > applications," John Pendry, a physicist at Imperial College in London in
      > the UK, told the publication. "It could find uses in stealth technology
      > and camouflage."
      > But Engheta, co-developer of the idea, said such applications can't even
      > be considered yet.
      > "Things like airplanes are very complex objects - complex shape and
      > complex materials - and I do not know to what extent our concept can be
      > applicable to that," Engheta told LiveScience. "We are still in the
      > conceptual stage, and there are several important questions that have to
      > be answered before any practical scenario can be considered."
      > Plasmons are real
      > You've seen cloaking technology at work on television, when blue
      > backgrounds are used to make a person invisible. Alu and Engheta envision
      > something far more sophisticated.
      > Objects are visible in the optical range because they reflect light, a
      > process scientists call scattering. Objects absorb light, too, and what is
      > absorbed is not seen. The sky is blue because the atmosphere scatters blue
      > light more than red.
      > A plasmonic cloaker would resonate with a particular wavelength of light,
      > so that the wavelength would not scatter.
      > Plasmons are real, a product of a strange characteristic of light, which
      > is made up of both particles and waves. Plasmons are created when
      > electrons on the surface of a metallic material move in rhythm. They have
      > other odd properties.
      > Back in 1998, researchers led by Thomas Ebbesen of the Louis Pasteur
      > University in Strasbourg, France shone light on a sheet of gold foil that
      > contained millions of tiny holes. The holes were smaller than the
      > wavelength of the light, and Ebbesen expected no light to get through.
      > Amazingly, more light came out the other side than what hit the holes.
      > Follow-up research found that plasmons - jittery little waves on the
      > surface of the metal - were snagging light and stuffing it through the
      > holes. "When the energy and momentum of the photons match the energy and
      > momentum of the plasmons, the photons are absorbed and radiated again on
      > the other side," according to an article in the May 1998 edition of
      > Photonics Spectra magazine.
      > Reality sets in
      > Engheta and Alu say objects coated with perhaps loops or coils of silver
      > or gold might do the trick.
      > But there are many hurdles. It is not clear how even a small object could
      > disappear in daylight, which itself contains many different wavelengths,
      > or colors, of light. Presumably a plasmonic device would have to be built
      > to cloak each wavelength.
      > Anything not perfectly ball-shaped presents additional problems. The
      > researchers' calculations suggest "homogeneous spherical objects" in the
      > nanoscale range - really, really small - could be rendered optically
      > invisible.
      > Practically speaking, the technology, if developed, might be used in
      > antiglare materials or to improve microscopic imaging in about five years,
      > Engheta said.
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