Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Revolutionary tungsten photonic crystal could provide more power for electrical devices

09.07.2003


Energy emissions far greater than predicted by Planck’s Law



You can’t get something for nothing, physicists say, but sometimes a radical innovation can come close.

Researchers at Sandia National Laboratories -- exceeding the predictions of a 100-year-old law of physics -- have shown that filaments fabricated of tungsten lattices emit remarkably more energy than solid tungsten filaments in certain bands of near-infrared wavelengths when heated.


This greater useful output offers the possibility of a superior energy source to supercharge hybrid electric cars, electric equipment on boats, and industrial waste-heat-driven electrical generators. The lattices’ energy emissions put more energy into wavelengths used by photovoltaic cells that change light into electricity to run engines.

Because near-infrared is the wavelength region closest to visible light, the day may not be distant when tungsten lattice emissions realized at visible wavelengths provide a foundation for more efficient lighting -- the first significant change in Edison’s light bulb since he invented it.

"This is an important and elegant work," says Cal Tech professor Amnon Yariv of the research achievement. Yariv is a member of the National Academy of Engineering and a leading figure in quantum optics research.

The work has been granted two patents with another pending. Two papers describing the advance have been accepted by the journal Optics Letters. Another will be published by Applied Physics Letters.

Sub-micron-featured lattices -- which resemble very tiny garden lattices carefully stacked one atop the other -- can be mass-produced cheaply with today’s computer-chip technologies.

The lattice itself can be visualized as a construction built of a child’s Lincoln Logs. The tungsten "logs" of this experiment have diameters of 0.5 microns separated by distances of 1.5 microns.

The lattices are also known as photonic crystals because of the crystalline regularity of the spacing of their components. At first such crystals were of interest because they could bend specific frequencies of light without loss of energy. This was because the crystal’s channels were constructed of exactly the right dimensions to form a ’home’ for particular wavebands as they travelled. 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 Planck

The demonstration, led by Sandia physicist Shawn Lin, exceeds in output 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 somewhat startling Sandia results exceeded these predictions by four to 10 times at near-infrared frequencies, says Lin.

In terms of electrical output, for the Sandia lattice heated in a vacuum to 1,250 degrees C -- the typical operating temperature of a thermal photovoltaic generator -- a conversion efficiency of 34 percent was calculated, three times the performance of an ideal blackbody radiator, predicted to be 11 percent.

Electrical power density was calculated to be approximately 14 watt/cm squared, rather than three watt/cm squared 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 group’s work does not break Planck’s law but only 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 a super cat,"he says.

A photonic lattice apparently subjects energies passing through its links and cavities to more complex photon-tungsten interactions than Planck dreamt of when he derived his system that successfully predicted the output energies of simple heated solids. And a lattice’s output is larger than a solid’s only in the frequency bands the lattice’s inner dimensions permit energy to emerge in.

Still, says Kazuaki Sakoda of Japan’s Nanomaterials Laboratory at the National Institute for Materials Science, "One of the most important issues in contemporary optics is the modification of the 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. To my knowledge, [Lin’s papers] are the first experimental report on this matter."

Sakoda’s book, Optical Properties of Photonic Crystals, was published by Springer Verlag, Berlin, 2001.

Theoretically, there are still unresolved questions as to how the process works without contradicting other physical laws.

Nevertheless, MIT physics professor John Joannopoulus in response to a question from a Sandia interviewer had high praise for the work. "It is definitely not a -- how did you put it -- ’a small step forward,’ it’s really a leap forward. It is a very clever completely believable ... I think it’s an exciting experiment, very carefully done, and there’s some really interesting new science here." Joannopoulus is a pioneer in photonic lattices and wrote the first book on the field.

The scientist at rest

Standing in his equipment-cluttered laboratory, Shawn Lin grins happily among the vandalized wreckage of a number of ordinary light bulbs from K-Mart. His team pirates the bulbs’ screw-in bases and glass filament supports for use as cheap, pre-made connectors and supports for the iridescent slivers of photonic lattice his team substitutes for common filaments of solid tungsten.

"Look!" Shawn says with obvious anticipation, and flips a switch connected to where the reconstituted filament sits in a vacuum chamber.

In its little chamber, like a kind of witches’ 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 are that far along!" Lin says with satisfaction.

If these results at 1.5 microns can be extended to the visible spectrum, ramifications of this work may help form the next generation of lighting after the currently more mature LED technology.



The increased amount of usable energy available from lattices (also known as photonic crystals) at specific frequencies is important to engineers dealing with electricity-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.

While such engines -- best known in the form of electric-powered cars " exist, their efficiencies 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 frequency bands.

While some energy is lost in this process, it makes available energies from frequencies previously unusable.

Visit the past

A year ago (Nature, May 2, 2002), Lin’s team showed that a tungsten lattice could gather absorbed energies at shorter wavelengths than ordinary tungsten could. Now, Lin with colleagues Jim Fleming, Jim Moreno (ret.), and Ihab El-Kady show actual emissions. The emission measurements were performed with the technical assistance of Jim Bur and Jonathan Rivera. Part of the earlier simulation of tungsten lattice’s optical properties was done at Iowa State University/Ames National Laboratory, in work led by Professor Kai Ming Ho.

The current use of tiny lattices to emanate energy in designated wave bands is a conceptual jump from their earliest appearances over a decade ago, when it was thought their major function would be to bend light without loss for telecommunications. Such lattices were built from semiconductor materials. In the case discussed here, semiconductor materials are used to form a lattice mold into which tungsten is introduced. The semiconductor material is then etched away, resulting in a thin tungsten photonic crystal sample about five micrometers thick.


Sandia National Laboratories’ World Wide Web home page is located at http://www.sandia.gov. Sandia news releases, image gallery, and periodicals can be found at the News and Events button.

Neal Singer | EurekAlert!
Further information:
http://www.sandia.gov/

More articles from Physics and Astronomy:

nachricht UNH scientists help provide first-ever views of elusive energy explosion
16.11.2018 | University of New Hampshire

nachricht NASA keeps watch over space explosions
16.11.2018 | NASA/Goddard Space Flight Center

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: UNH scientists help provide first-ever views of elusive energy explosion

Researchers at the University of New Hampshire have captured a difficult-to-view singular event involving "magnetic reconnection"--the process by which sparse particles and energy around Earth collide producing a quick but mighty explosion--in the Earth's magnetotail, the magnetic environment that trails behind the planet.

Magnetic reconnection has remained a bit of a mystery to scientists. They know it exists and have documented the effects that the energy explosions can...

Im Focus: A Chip with Blood Vessels

Biochips have been developed at TU Wien (Vienna), on which tissue can be produced and examined. This allows supplying the tissue with different substances in a very controlled way.

Cultivating human cells in the Petri dish is not a big challenge today. Producing artificial tissue, however, permeated by fine blood vessels, is a much more...

Im Focus: A Leap Into Quantum Technology

Faster and secure data communication: This is the goal of a new joint project involving physicists from the University of Würzburg. The German Federal Ministry of Education and Research funds the project with 14.8 million euro.

In our digital world data security and secure communication are becoming more and more important. Quantum communication is a promising approach to achieve...

Im Focus: Research icebreaker Polarstern begins the Antarctic season

What does it look like below the ice shelf of the calved massive iceberg A68?

On Saturday, 10 November 2018, the research icebreaker Polarstern will leave its homeport of Bremerhaven, bound for Cape Town, South Africa.

Im Focus: Penn engineers develop ultrathin, ultralight 'nanocardboard'

When choosing materials to make something, trade-offs need to be made between a host of properties, such as thickness, stiffness and weight. Depending on the application in question, finding just the right balance is the difference between success and failure

Now, a team of Penn Engineers has demonstrated a new material they call "nanocardboard," an ultrathin equivalent of corrugated paper cardboard. A square...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Optical Coherence Tomography: German-Japanese Research Alliance hosted Medical Imaging Conference

19.11.2018 | Event News

“3rd Conference on Laser Polishing – LaP 2018” Attracts International Experts and Users

09.11.2018 | Event News

On the brain’s ability to find the right direction

06.11.2018 | Event News

 
Latest News

New materials: Growing polymer pelts

19.11.2018 | Materials Sciences

Earthquake researchers finalists for supercomputing prize

19.11.2018 | Information Technology

Controlling organ growth with light

19.11.2018 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>