New approach using nanoparticle alloys allows heat to be focused or reflected just like electromagnetic waves

An MIT researcher has developed a technique that provides a new way of manipulating heat, allowing it to be controlled much as light waves can be manipulated by lenses and mirrors.

The approach relies on engineered materials consisting of nanostructured semiconductor alloy crystals. Heat is a vibration of matter—technically, a vibration of the atomic lattice of a material—just as sound is. Such vibrations can also be thought of as a stream of phonons—a kind of "virtual particle" that is analogous to the photons that carry light.

The new approach is similar to recently developed photonic crystals that can control the passage of light, and phononic crystals that can do the same for sound. The spacing of tiny gaps in these materials is tuned to match the wavelength of the heat phonons, explains Martin Maldovan, a research scientist in MIT's Department of Materials Science and Engineering and author of a paper on the new findings published Jan. 11 in the journal Physical Review Letters.

"It's a completely new way to manipulate heat," Maldovan says. Heat differs from sound, he explains, in the frequency of its vibrations: Sound waves consist of lower frequencies (up to the kilohertz range, or thousands of vibrations per second), while heat arises from higher frequencies (in the terahertz range, or trillions of vibrations per second).