A specially formed material that can provide custom broadband absorption in the infrared can be identified and manufactured using "genetic algorithms," according to Penn State engineers, who say these metamaterials can shield objects from view by infrared sensors, protect instruments and be manufactured to cover a variety of wavelengths.
"The metamaterial has a high absorption over broad bandwidth," said Jeremy A. Bossard, postdoctoral fellow in electrical engineering. "Other screens have been developed for a narrow bandwidth, but this is the first that can cover a super-octave bandwidth in the infrared spectrum."
Having a broader bandwidth means that one material can protect against electromagnetic radiation over a wide range of wavelengths, making the material more useful. The researchers looked at silver, gold and palladium, but found that palladium provided better bandwidth coverage. This new metamaterial is actually made of layers on a silicon substrate or base. The first layer is palladium, followed by a polyimide layer. On top of this plastic layer is a palladium screen layer. The screen has elaborate, complicated cutouts—sub wavelength geometry—that serve to block the various wavelengths. A polyimide layer caps the whole absorber.
"As long as the properly designed pattern in the screen is much smaller than the wavelength, the material can work effectively as an absorber," said Lan Lin, graduate student in electrical engineering. "It can also absorb 90 percent of the infrared radiation that comes in at up to a 55 degree angle to the screen."