An international research team has used a “thermal metamaterial” to control the emission of radiation at high temperatures, an advance that could bring devices able to efficiently harvest waste heat from power plants and factories.
Roughly 50 to 60 percent of the energy generated in coal and oil-based power plants is wasted as heat. However, thermophotovoltaic devices that generate electricity from thermal radiation might be adapted to industrial pipes in factories and power plants, as well as on car engines and automotive exhaust systems, to recapture much of the wasted energy.
In new findings, researchers demonstrated how to restrict emission of thermal radiation to a portion of the spectrum most needed for thermophotovoltaic technology.
“These devices require spectrally tailored thermal emission at high temperatures, and our research shows that intrinsic material properties can be controlled so that a very hot object glows only in certain colors,” said Zubin Jacob, an assistant professor of electrical and computer engineering at Purdue University. “The main idea is to start controlling thermal emission at record high temperatures in ways that haven’t been done before.”
The thermal metamaterial – nanoscale layers of tungsten and hafnium oxide – was used to suppress the emission of one portion of the spectrum while enhancing emission in another. (An animation is available at https://youtu.be/dbePERsPh-g)
Metamaterials are composite media that contain features, patterns or elements such as tiny nanoantennas that enable an unprecedented control of light. Under development for about 15 years, the metamaterials owe their unusual abilities to precision design and manufacture on the scale of nanometers.
“They have been used mainly to manipulate coherent light, as in a laser, but the ability to manipulate infrared thermal radiation at 1,000 C opens up new areas of research,” Jacob said. “The technique we used to achieve this thermal suppression and enhancement is fundamentally different from existing thermal engineering approaches and harnesses a phenomenon called topological transitions.”
Findings were detailed in a research paper published earlier this year in the journal Nature Communications. The work was performed by researchers at Purdue, the Hamburg University of Technology in Germany; University of Alberta in Canada; and Helmholtz-Zentrum Geesthacht Centre for Materials and Coastal Research in Germany. The co-lead authors were Hamburg University of Technology postdoctoral researcher Pavel Dyachenko and University of Alberta doctoral student Sean Molesky.
The research represents the first time the approach was used for thermal emission in high-temperature metamaterials, also called refractory metamaterials.
“My student, Sean Molesky, theoretically predicted it in 2012, and it has taken about four years and some exceptional materials engineering from our collaborators to perform the high-temperature experiments and demonstrate the thermal metamaterial,” Jacob said.
The basic operating principle of a photovoltaic cell is that a semiconducting material is illuminated with light, causing electrons to move from one energy level to another. Electrons in the semiconductor occupy a region of energy called the valence band while the material is in the dark. But shining light on the material causes the electrons to absorb energy, elevating them into a region of higher energy called the conduction band. As the electrons move to the conduction band, they leave behind “holes” in the valance band. The region between both bands, where no electrons exist, is called the band gap.
“If you have energy below the band gap, that is generally wasted,” Jacob said. “So what you want to do for high-efficiency thermal energy conversion is suppress the thermal emission below the band gap and enhance it above the band gap, and this is what we have done. We have used the topological transition in a way that was not done before for thermal enhancement and suppression, enhancing the high-energy part of the emission spectrum and suppressing the low-energy thermal photons. This allows us to emit light only within the energy spectrum above the band gap.”
The paper’s other authors were Jacob; Hamburg University of Technology researchers Alexander Yu Petrov, Slawa Lang, Manfred Eich, T. Krekeler and M. Ritter; and senior research scientist Michael Störmer from the Helmholtz-Zentrum Geesthacht Centre for Materials and Coastal Research.
Future research will include work to convert heat radiation from a thermal metamaterial to electron-hole pairs in a semiconducting material, a critical step in developing the technology. The thermophotovoltaic technology might be ready for commercialization within seven years, Jacob said.
A graphic depicting the high-temperature thermal metamaterial is available athttps://news.uns.purdue.edu/images/2016/jacob-topological.jpg
The graphic depicts how the thermal radiation is controlled using the shape of the surfaces: the metamaterial enhances thermal radiation in the “ellipsoidal regime” at left, but suppresses it in the “hyperboloidal regime” at right.
The Latest on: Thermal metamaterial
via Google News
The Latest on: Thermal metamaterial
- Thin-film-based optical cavity coupling enhances broadband thermal emissionon May 31, 2019 at 5:00 pm
Although the thermal radiation of thin-film-emitter-based sources can be enhanced by photonic-crystal cavities, plasmonic antennas, or metamaterial-based microstructures, the enhancement is typically ... […]
- Manufacturing Bits: April 8on April 8, 2019 at 12:11 am
We could say: ‘Here is the behavior I want. Now tell me what the metamaterial looks like. ’” With metamaterials, researchers have developed an ultra-narrowband wavelength-selective thermal emitter. ... […]
- A 90-nm-thick graphene metamaterial for strong and extremely broadband absorption of unpolarized lighton March 18, 2019 at 9:05 am
The metamaterial consists of alternating graphene and dielectric ... The very broad spectral and angular responses of the absorber are ideal for solar thermal applications, as we illustrate by showing ... […]
- Design and validation of world-class multilayered thermal emitter using machine learningon March 15, 2019 at 8:46 am
Scientists designed a multilayered metamaterial that realizes ultra-narrowband wavelength-selective thermal emission by combining the machine learning (Bayesian optimization) and thermal emission ... […]
- Design and validation of world-class multilayered thermal emitter using machine learningon March 15, 2019 at 6:25 am
NIMS, the University of Tokyo, Niigata University and RIKEN have jointly designed a multilayered metamaterial that realizes ultra-narrowband wavelength-selective thermal emission by combining the ... […]
- Metamaterial for elastostatic cloaking under thermal gradientson March 4, 2019 at 4:00 pm
We introduce the optimization-based method for the design of thermo-mechanical metamaterials and, particularly, for the elastostatic cloaking under thermal loads. It consists of solving a large-scale, ... […]
- New metamaterial shrinks when the heat is onon October 25, 2018 at 5:00 pm
Developed as part of DARPA's program to study materials with controlled microstructure architecture, the lightweight metamaterial exhibits what the researchers call "negative thermal expansion." ... […]
- Metamaterial coatings for spacecraft could save big on launch weighton April 25, 2018 at 4:30 am
A pan-European consortium has developed a new type of metamaterial surface coating to assist in the thermal control of spacecraft. Known as metamaterial Optical Solar Reflectors (meta-OSRs), the ... […]
- Graphene-ceramic metamaterial shows promise in sensors and heat shieldson August 10, 2017 at 2:39 am
A new lightweight, flame-resistant and super-elastic metamaterial combines high strength with electrical conductivity and thermal insulation for applications ranging from heat shields to sensors. ... […]
via Bing News