Caltech Researchers Make Groundbreaking Discovery in Energy-Harvesting Device

In a groundbreaking development, scientists at Caltech have created a revolutionary device that challenges a fundamental law of physics related to energy absorption and emission. The device, invented in the lab of Harry Atwater, a renowned Caltech physicist, offers promising implications for sustainable energy harvesting and the development of certain kinds of camouflage.

For over a century and a half, scientists have adhered to Kirchhoff’s law of thermal radiation, a principle proposed by Gustav Kirchhoff in 1860. This law stated that the efficiency of absorbing and emitting energy in the form of electromagnetic radiation must be equal at every wavelength and angle of incidence.

However, Caltech’s new research, led by electrical engineering graduate student Komron Shayegan, has now demonstrated that this long-standing law can be broken. “This experimental proof challenges Kirchhoff’s law, which has been upheld for more than 150 years,” said Professor Atwater.

The breakthrough is centered around decoupling the relationship between an object’s ability to absorb and emit energy. In the past, designing devices that absorbed and emitted energy relied on maintaining a one-to-one equality between absorptivity and emissivity. But now, researchers have found that by breaking this equality, they can achieve higher energy conversion efficiencies, particularly in energy-harvesting systems.

To illustrate this concept, Shayegan used the example of a photovoltaic (solar panel). Traditionally, if a solar panel absorbed energy from the sun but emitted some of it back as heat, that energy would be lost for practical purposes. However, with the new device, the absorbed radiation can be redirected towards another energy-harvesting object, maximizing energy conversion potential.

The device developed by the researchers utilizes a moderate magnetic field and a patterned structure to enhance absorption and emission in infrared wavelengths. Notably, the effect of breaking Kirchhoff’s law can be observed simply by heating the device above room temperature and comparing its emissive efficiency to its absorptive efficiency.

The study, titled “Direct Observation of Kirchhoff Thermal Radiation Law Violation,” has been published in the prestigious journal Nature Photonics. The research team includes scientists from Caltech, Stanford University, the University of Houston, and is led by Professor Harry Atwater.

Apart from the potential for more efficient energy harvesting systems, the discovery may also have exciting applications in the development of advanced camouflage technologies. This breakthrough opens up new possibilities for harnessing and controlling energy in novel ways, paving the way for a more sustainable and technologically advanced future.

Funding for the research was provided by the Defense Advanced Research Projects Agency, Caltech reported.