Blunderov
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"We think in generalities, we live in details"
  
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RE: virus: Taking on Planck - Popular Mechanics
« on: 2003-09-02 15:45:35 » |
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Very belatedly I have discovered this marvelous magazine. An Aladdin's
cave of desirable hi-tech toys for (sometimes)geekish boys too. Who, for
instance, could possibly want to be without the "Nitemax Digital Night
Vision Viewing System" with RCA video-out jack for transmitting to
camcorders, VCR's or PCs? Certainly not me.
<q>
Taking on Planck
YOU can't get something for nothing, physicists say, but sometimes a
radical innovation effectively provides just that.
Researchers at Sandia National Laboratories in the US have shown that
filaments fabricated from microscopic tungsten lattices, and then
heated, emit remarkably more energy in a band of near infrared
wavelengths than solid tungsten filaments. This greater output offers
the possibility of a superior energy source for powering hybrid electric
cars, electric equipment on boats, and industrial waste heat driven
electrical generators.
The lattices' energy emissions are at the right wavelengths to meet the
specifications of photocells that currently change light into
electricity to run engines. Because near infrared is the wavelength
region closest to visible light, tungsten lattice emissions at visible
wavelengths could provide a foundation for more efficient lighting in
the near future. "This is an important and elegant work," says Caltech
professor Amnon Yariv, a member of the US National Academy of
Engineering and a leading figure in quantum optics research.
Sub-micron-featured-lattices -which resemble very tiny garden trellises
carefully stacked one atop the other -can be fabricated cheaply with
today's computer chip technologies. They are also known as photonic
crystals because of the crystalline regularity of the spacing of their
components. At first the crystals were of interest primarily because
they could bend
specific frequencies of light without any loss of energy. This was
because the crystal's channels were constructed of exactly the right
dimensions to form a "home" for particular wavebands The innovation of
the current method is to use the channels not to bend light, but to
permit input energy to exit only in the desired frequency bands.
The shadow of Max Plank
The demonstration, led by Sandia physicist Shawn Lin, at first seemed to
flout a well known law formulated a century ago by Max Planck, one of
the founders of modern physics. The equation, called Planck's Law of
Blackbody Cavity Radiation, predicts the maximum emissions expected at
any wavelength from ideal solids. The Sandia group exceeded these
predictions by wide margins.
When the lattice was heated in a vacuum to 1 250 degrees C -the typical
operating temperature of a thermal photovoltaic generator -a conversion
efficiency of 34 per cent was calculated. That's three times the
performance of an ideal blackbody radiator, predicted to be 11 per cent.
Electrical power density was calculated to be about 14 wattIcM2, rather
than the three watt/CM2 expected from an ideal blackbody radiator. No
deterioration of the tungsten lattice was observed, although long term
tests have yet to be run.
Cat vs supercat
Lin says his groups work does not break Planck's law, but modifies it by
demonstrating the creation of a new class of emitters."To compare the
amounts of emissions from a solid and a photonic lattice is like
comparing a dog and a cat, or a cat and superrcat," he says.
A heated photonic lattice subjects energies passing through its links
and cavities to more complicated interactions than Planck dreamt of when
he derived his formula that successfully predicted the output energies
of simple heated solids, says Lin. Lattice results from More complex
photon tungsten interaction than the system Planck formulated. A
lattice's output can be considerably larger than a solid's but only in
the frequency bands the lattice's inner dimensions permit energy to
emerge in.
Kazuaki Sakoda of Japan's Nanomaterials Laboratory at National institute
for Materials Science: "One of the most important issues in contemporary
optics is the modification of nature of the radiation field and its
interaction with matter. Lin's recent work clearly demonstrates that
even Planck's law - the starting point of the era of quantum mechanics
(used to predict these interactions) -can be modified."
Standing in his equipment cluttered laboratory Lin grins happily among
the vandalised wreckage of a number of ordinary light bulbs from the
local supermarket. His team pirates the screw in bases and glass
filament supports for use as cheap, pre-made connectors and supports for
the iridescent slivers of photonic lattices -the size and shape of
ordinary filaments
-that substitute for common filaments of tungsten.
"Look!" Lin says with obvious anticipation, and flips a switch connected
to where the reconstituted filament sits in a vacuum chamber. Inits
little chamber, like a kind of witch Sabbath for light bulbs, the bulb,
though formerly dead, now glows again, but with a distinctly yellow
light. The lattice filament, powered by only two watts, and with most Of
its output keyed to the infrared range at 1,5 to 2 Microns, has enough
of a tail into the visible spectrum for the lattice to glow. "We're
that far along!" Lin says with satisfaction.
If these results at 1,5 Microns can be extended to the visible spectrum,
the team will be well on their way to the next generation of lighting
after the more mature LED technology. The increased amount of energy
available from lattices (also known as photonic crystals) at specific
frequencies is important to engineers dealing with heat driven engines.
A photonic lattice
absorbing energies from a power plant generator's excess heat could
release it at higher frequencies readily absorbable by the Photovoltaic
Cell that powers electricity driven engines.
The efficiencies of these engines have been much lower than hoped
because their receivers cannot absorb incoming energies across the wide
spectrum of infrared radiation generated as unwanted heat, but only from
limited bands within the broad range. Here the lattice could serve as a
kind of funnel, forcing the heat radiation into predetermined frequency
bands.
When placed between the generator -be it solar, dynamo, or fire -and
receiver, the metallic photonic lattice can be engineered to absorb
energies, become thermally excited, and release them in only a few
frequencies. While some energy is lost in this process, it makes
available the far greater energies that were previously unusable.
There are still unresolved questions about how the process works without
contradicting certain physical laws, but that's a mere bagatelle. The
future has arrived and it's brighter than we thought.
PM
</q>
See also http://www.sandia.gov/media/NewsRel/NR2002/tungsten.htm
<q>
A cool tungsten light bulb may be possible
Tungsten photonic lattice changes heat to light </q>
As some of you may know, I am a television lighting designer, and this
development will be most welcome in the film and television industry. It
has often occurred to me that the "luminaires" we use should more
properly be referred to as "heaters" converting as they do, only about
25% of the energy that is supplied to them into light. The rest, of
course, is heat.
This can make working conditions for artists, especially in African
studios during Summer, quite uncomfortable. Also it seems that useful
light levels could be attained using less power.
Best Regards
Blunderov
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