Posted on 07/28/2023 10:44:15 AM PDT by Red Badger
Researchers have developed a device that can disrupt the relationship between the absorption and emission efficiencies of an object, essentially violating Kirchhoff’s law of thermal radiation. This law, in place for over 150 years, states that an object’s ability to absorb and emit energy is equal at each wavelength and angle of incidence. This breakthrough could significantly impact sustainable energy harvesting systems and certain types of camouflage technology. (Artist’s concept.)
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Scientists have developed a device that can break the principles of Kirchhoff’s law of thermal radiation, disrupting the traditional relationship between absorption and emission efficiencies in an object. This novel approach could enhance the efficiency of energy-harvesting systems and affect camouflage technologies.
If you take an object and set it out in the sun, it will begin to warm up. This is because it is absorbing energy from the sun’s rays and converting that energy to heat. If you leave that object outside it will continue getting warmer, but only to a point. A sunbather lying on a beach won’t catch fire, after all.
As objects (or people) absorb energy (light from the sun), they also emit energy (infrared radiation, or heat). This is something you may have experienced while walking past a block wall on a summer afternoon and feeling heat emanating from it.
Understanding Kirchhoff’s Law The connection between an object’s ability to absorb and emit energy in the form of electromagnetic radiation—its absorptive and emissive efficiencies—has long been explained by something known as Kirchhoff’s law of thermal radiation. The law, a concept devised by Gustav Kirchhoff in 1860, which states absorptive and emissive efficiencies are equal at each wavelength and angle of incidence. (A more in-depth explanation of Kirchhoff’s law can be found here.)
Breaking Kirchhoff’s Law A new device developed in the lab of Harry Atwater, the Howard Hughes Professor of Applied Physics and Materials Science, breaks that normally tight relationship between the absorbed and emitted efficiencies of an object. The invention may also have important implications for sustainable energy harvesting systems and the development of certain kinds of camouflage.
“Kirchhoff’s law has been upheld for more than 150 years, and while theoretical proposals for its violation have been advanced before, this is the first experimental proof that this law can be broken,” says Atwater.
Looking Into the Future of Energy Absorption Electrical engineering graduate student Komron Shayegan, lead author of the new research, further explains:
“The equality dictated by Kirchhoff’s law has been a guiding principle in the design of devices that absorb and emit energy in the form of radiation, because by designing around and measuring the absorptive properties of a material, we get the emissive properties for free. However, there has been a recent shift when designing emitters/absorbers, namely that we are trying to move beyond having a simple one-to-one equality between the emissivity and absorptivity of a body. “One motivation behind decoupling the two is in energy-harvesting systems. For example, if an energy-harvesting object, like a photovoltaic (solar panel), is re-emitting some of its absorbed energy back toward the energy source (the Sun) as heat, that energy is lost to human purposes. In theory, if the photovoltaic— or other energy-harvesting object —were to re-emit absorbed radiation away from the source and toward yet another energy-harvesting object, one could reach higher energy conversion efficiencies.
“Our study shows that it is possible to break the equality of Kirchhoff’s law of thermal radiation with a device placed in a moderate magnetic field. The device itself combines a material that has a strong magnetic-field response with a patterned structure that enhances absorption and emission in infrared wavelengths. What is particularly exciting is that we can observe the effect by simply heating the device above room-temperature and directly comparing the emissive efficiency to the absorptive efficiency.”
The paper describing the work, “Direct Observation of Kirchhoff Thermal Radiation Law Violation,” appears in the July 24 issue of the journal Nature Photonics.
Reference: “Direct observation of the violation of Kirchhoff’s law of thermal radiation” by Komron J. Shayegan, Souvik Biswas, Bo Zhao, Shanhui Fan and Harry A. Atwater, 24 July 2023, Nature Photonics. DOI: 10.1038/s41566-023-01261-6
Co-authors are Souvik Biswas, formerly of Caltech and now at Stanford University; Bo Zhao of the University of Houston; Shanhui Fan of Stanford University; and Harry Atwater, who is also the Otis Booth Leadership Chair of the Division of Engineering and Applied Science and director of the Liquid Sunlight Alliance.
Funding for the research was provided by the Defense Advanced Research Projects Agency.
You know that is the first thing I thought of too.
The most important thing that learned from Star TreK:
Never wear a red uniform
If true, is a breakthrough with vast implications.
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ok. like what?
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There was a great documentary from 2005: “How William Shatner Changed the World,” hosted by Shatner himself, that showed how many of today’s gadgets were anticipated by the original Star Trek series.
Right U R.
Well it is still into the future and I have confidence real men will re-discover the allure of the feminine physique. Plus we don’t have teleporters yet, so there’s still time.
I’m no physicist, duh, but it sounds like thermal radiation is just waste radiation from heat when it is in excess of what can be used and these scientists have managed to figure out how to keep it from being wasted, resulting in a reduction or prevention of thermal radiation. It could be useful for maybe making cars more efficient, if it can be adapted.
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is the heat that is generated by a coal oil natural gas oven or aj nuclear reaction considered to be waste heat? If that heat could be turned directly into electricity —then it really is revolutionary.
if waste heat from say a nuclear reaction could be turned into electricity—then yeah this would be revolutionary. but I can’t say that I know what’s going on.
I hear you, but even nuclear power plants are only about 33% efficient for energy transfer to power for your home. That’s a lot of waste energy. If they can increase the efficiency, that’s untold billion that could be saved.
Well said !
The way I read it, the “waste” energy (e.g., infrared) is re-emitted at a different *angle* than the incoming energy (e.g., visible light). This means that whatever collects it needn’t block the incoming radiation. This could allow two-stage electricity generation using two different kinds of photocells (for the different wavelengths).
(I sort of remember reading about two-stage steam systems the used the low pressure steam that came out of the turbine to run the pumps or some such.)
Buddy of mine worked at a utility & said they found a guy in the boonies living in a tent under the transmission lines. He was getting his electricity by wrapping heavy copper around railroad ties. He didn’t have much but I guess it was enough for his tent. They found him during routine inspections & threatened to call the sheriff for stealing electricity unless he took it apart.
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