A bendable sheet of silicon can hide 95 percent of infrared light, rendering objects essentially invisible to heat-sensing night vision goggles or infrared cameras.
Black silicon is made by growing silicon crystals at various heights on a silicon wafer, creating what looks like a dense forest of needles. This material hardly reflects any visible light, because light waves bounce back and forth between the steeple-like silicon towers, preventing their escape.
Hongrui Jiang at the University of Wisconsin-Madison and his colleagues wondered if this property could be extended to other parts of the electromagnetic spectrum.
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By scattering silver nanoparticles 鈥� which efficiently absorb infrared light聽-on the silicon forest floor, they created a sheet in which infrared light more or less disappears.
Hidden heat
The team also placed the silicon and silver material on a rubbery layer etched with grooves to funnel waste heat into the surrounding air. This small amount of heat should blend in with background sources, says Jiang, which actually makes it a better invisibility cloak 鈥� a completely dark spot of infrared light would probably look suspicious to anyone seeking out heat signatures.
To test their cloak, the team heated a model in the shape of a human to body temperature and a model of a jeep to around 40 掳C. The flexible sheet rendered both virtually undetectable.
Jiang says the cloak has obvious military applications 鈥淚f you have someone hiding in the bush or you have a tank running with a hot engine, and someone is trying to detect these object with a thermal camera, this is a counter measure,鈥� he says.
Advanced Engineering Materials
