Stealth sheet cloaks heat signature of people and vehicles

(Credit: Hongrui Jiang)

To trap the infrared light, the researchers used a material called black silicon, which is also highly effective at absorbing visible light and is commonly used in solar cells. Black silicon absorbs light because it consists of millions of nanowires all pointing upward like a densely-packed forest. Incoming light reflects back and forth between the vertical spires, bouncing around within the material instead of escaping.

The nanowires were made using tiny particles of silver to help etch the material down into a thin layer of solid silicon, which results in a thicket of microscopic needles that are taller than those which only absorb visible light. Both the nanowires and the silver particles contribute to absorbing infrared light. The stealth material was then transferred onto thin flexible substrates to create the IR stealth cloak.

"What we have shown is an ultrathin stealth 'sheet,'” said study leader Hongrui Jiang, professor of electrical and computer engineering at the University of Wisconsin-Madison.