The technology, developed at the U.S. Department of Energy's Idaho National Laboratory, is the first step toward a solar energy collector that could be mass-produced on flexible materials.
While methods to convert the energy into usable electricity still need to be developed, the sheets could one day be manufactured as lightweight "skins" that power everything from hybrid cars to iPods with higher efficiency than traditional solar cells, say the researchers, who report their findings Aug. 13 at the American Society of Mechanical Engineers 2008 2nd International Conference on Energy Sustainability in Jacksonville, Fla. The nanoantennas also have the potential to act as cooling devices that draw waste heat from buildings or electronics without using electricity.
The nanoantennas target mid-infrared rays, which the Earth continuously radiates as heat after absorbing energy from the sun during the day. In contrast, traditional solar cells can only use visible light, rendering them idle after dark. Infrared radiation is an especially rich energy source because it also is generated by industrial processes such as coal-fired plants.
"Every process in our industrial world creates waste heat," says INL physicist Steven Novack. "It's energy that we just throw away." Novack led the research team, which included INL engineer Dale Kotter, W. Dennis Slafer of MicroContinuum, Inc. (Cambridge, Mass.) and Patrick Pinhero, now at the University of Missouri.
The nanoantennas are tiny gold squares or spirals set in a specially treated form of polyethylene, a material used in plastic bags. While others have successfully invented antennas that collect energy from lower-frequency regions of the electromagnetic spectrum, such as microwaves, infrared rays have proven more elusive. Part of the reason is that materials' properties change drastically at high-frequency wavelengths, Kotter says.
The researchers studied the behavior of various materials -- including gold, manganese and copper -- under infrared rays and used the resulting data to build computer models of nanoantennas. They found that with the right materials, shape and size, the simulated nanoantennas could harvest up to 92 percent of the energy at infrared wavelengths.
The team then created real-life prototypes to test their computer models. First, they used conventional production methods to etch a silicon wafer with the nanoantenna pattern. The silicon-based nanoantennas matched the computer simulations, absorbing more than 80 percent of the energy over the intended wavelength range. Next, they used a stamp-and-repeat process to emboss the nanoantennas on thin sheets of plastic. While the plastic prototype is still being tested, initial experiments suggest that it also captures energy at the expected infrared wavelengths.
The nanoantennas' ability to absorb infrared radiation makes them promising cooling devices. Since objects give off heat as infrared rays, the nanoantennas could collect those rays and re-emit the energy at harmless wavelengths. Such a system could cool down buildings and computers without the external power source required by air-conditioners and fans.
But more technological advances are needed before the nanoantennas can funnel their energy into usable electricity. The infrared rays create alternating currents in the nanoantennas that oscillate trillions of times per second, requiring a component called a rectifier to convert the alternating current to direct current. Today's rectifiers can't handle such high frequencies. "We need to design nanorectifiers that go with our nanoantennas," says Kotter, noting that a nanoscale rectifier would need to be about 1,000 times smaller than current commercial devices and will require new manufacturing methods. Another possibility is to develop electrical circuitry that might slow down the current to usable frequencies.
If these technical hurdles can be overcome, nanoantennas have the potential to be a cheaper, more efficient alternative to solar cells. Traditional solar cells rely on a chemical reaction that only works for up to 20 percent of the visible light they collect. Scientists have developed more complex solar cells with higher efficiency, but these models are too expensive for widespread use.
Nanoantennas, on the other hand, can be tweaked to pick up specific wavelengths depending on their shape and size. This flexibility would make it possible to create double-sided nanoantenna sheets that harvest energy from different parts of the sun's spectrum, Novack says. The team's stamp-and-repeat process could also be extended to large-scale roll-to-roll manufacturing techniques that could print the arrays at a rate of several yards per minute. The sheets could potentially cover building roofs or form the "skin" of consumer gadgets like cell phones and iPods, providing a continuous and inexpensive source of renewable energy.
Roberta Kwok | EurekAlert!
Laser sensor LAH-G1 - optical distance sensors with measurement value display
15.08.2017 | WayCon Positionsmesstechnik GmbH
Engineers find better way to detect nanoparticles
14.08.2017 | Washington University in St. Louis
Whether you call it effervescent, fizzy, or sparkling, carbonated water is making a comeback as a beverage. Aside from quenching thirst, researchers at the University of Illinois at Urbana-Champaign have discovered a new use for these "bubbly" concoctions that will have major impact on the manufacturer of the world's thinnest, flattest, and one most useful materials -- graphene.
As graphene's popularity grows as an advanced "wonder" material, the speed and quality at which it can be manufactured will be paramount. With that in mind,...
Physicists at the University of Bonn have managed to create optical hollows and more complex patterns into which the light of a Bose-Einstein condensate flows. The creation of such highly low-loss structures for light is a prerequisite for complex light circuits, such as for quantum information processing for a new generation of computers. The researchers are now presenting their results in the journal Nature Photonics.
Light particles (photons) occur as tiny, indivisible portions. Many thousands of these light portions can be merged to form a single super-photon if they are...
For the first time, scientists have shown that circular RNA is linked to brain function. When a RNA molecule called Cdr1as was deleted from the genome of mice, the animals had problems filtering out unnecessary information – like patients suffering from neuropsychiatric disorders.
While hundreds of circular RNAs (circRNAs) are abundant in mammalian brains, one big question has remained unanswered: What are they actually good for? In the...
An experimental small satellite has successfully collected and delivered data on a key measurement for predicting changes in Earth's climate.
The Radiometer Assessment using Vertically Aligned Nanotubes (RAVAN) CubeSat was launched into low-Earth orbit on Nov. 11, 2016, in order to test new...
A study led by scientists of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg presents evidence of the coexistence of superconductivity and “charge-density-waves” in compounds of the poorly-studied family of bismuthates. This observation opens up new perspectives for a deeper understanding of the phenomenon of high-temperature superconductivity, a topic which is at the core of condensed matter research since more than 30 years. The paper by Nicoletti et al has been published in the PNAS.
Since the beginning of the 20th century, superconductivity had been observed in some metals at temperatures only a few degrees above the absolute zero (minus...
16.08.2017 | Event News
04.08.2017 | Event News
26.07.2017 | Event News
18.08.2017 | Life Sciences
18.08.2017 | Physics and Astronomy
18.08.2017 | Materials Sciences