Researchers have developed a new type of thin, nonmetallic coating that can dramatically reduce heat transfer between nearby objects.
The technology could eventually help control temperatures in electronics, spacecraft, infrared sensors and other devices where traditional metal coatings are not ideal.
Scientists at the Advanced Science Research Center at the CUNY Graduate Center (CUNY ASRC) and Honeywell Aerospace created specially designed surfaces called metasurfaces.
In laboratory experiments, the coatings reduced thermal radiation emission by more than 80% compared with ordinary surfaces made from the same nonmetallic materials.
The results, published in Nature Communications, suggest a new way to manage radiant heat without relying on metals.
All objects give off energy as thermal radiation. At temperatures common in everyday technology, much of this energy is released as invisible infrared light.
When two objects face each other, infrared energy emitted by one can be absorbed by the other. If the objects are at different temperatures, this process allows heat to move between them even without physical contact.
Metals are often used to reduce this heat transfer because they reflect infrared radiation across a wide range of wavelengths. However, metals also conduct electricity. This can cause problems in sensitive electronics, optical equipment and thermoelectric devices. Metal coatings may also be difficult to integrate with some advanced materials.
Nonmetallic coatings could solve these problems, but researchers have struggled with an important limitation. Existing designs may strongly block infrared radiation over only a narrow range of wavelengths. Designs that work across a wider range often need to be much thicker.
The new study takes a different approach. Rather than designing one surface to reflect as much infrared radiation as possible, the researchers designed two facing surfaces to work together.
Each surface was engineered to interact with different parts of the infrared spectrum. When one surface strongly emits radiation at certain wavelengths, the other is designed to absorb very little radiation at those same wavelengths.
The researchers compare the idea to two radios operating on different channels. Both radios can transmit and receive signals, but because they are tuned to different frequencies, very little communication occurs between them.
To achieve this effect, the team built each metasurface from seven thin layers of dielectric, or electrically insulating, materials. These layers form structures called distributed Bragg reflectors, which can selectively reflect or transmit different wavelengths of light.
Importantly, the design does not require complicated nanoscale patterns. The layered coatings can be produced using established thin-film manufacturing techniques, potentially making the technology easier to develop for practical applications.
The coatings also continued to perform well over a broad range of temperatures and remained effective despite small variations that could occur during manufacturing.
The technology is still at the proof-of-concept stage, and additional testing will be needed. But the researchers believe it could eventually provide a useful new form of thermal insulation for spacecraft, electronics, sensors and other systems where electrically conductive metal coatings are undesirable.
Source: KSR.
