Stealth material hides hot objects from prying infrared eyes

Researchers at the University of Wisconsin-Madison (US) have developed a ‘stealth’ material that hides objects and people from infrared cameras.

Infrared cameras are tools to detect objects of people by the warmth they emit. They are used for example on drones to help find their targets in the dark or through heavy fog. Current shields against these cameras are made of heavy metal or thermal blankets.

The new cloaking material offers substantial improvements on other heat-masking technologies. The new material is very thin, less than one millimetre, as well as much lighter than thermal blankets or metal. The sheet absorbs approximately 94 per cent of the infrared light it encounters. By trapping so much light, the objects beneath the sheets become invisible for infrared cameras.

The stealth material is made with a material called black silicon, which is commonly integrated into solar cells. Black silicon absorbs light, because it consists of millions of microscopic needles, known as nanowires. These needles all point upward. Incoming light reflects back and forth between the spires, bouncing around within the material, rather than reflecting back. The material has long been known to absorb visible light, but this is the first time it’s used to trap infrared light.

The researchers boosted the silicon’s properties by elongating the nanowires, using tiny particles of silver, which also help to absorb infrared light. They also added a flexible backing interspersed with small air channels. These channels prevent the sheet from heating up too quickly as it absorbs infrared light.

The researchers also incorporated electronic heating elements into the stealth material. These could fool infrared cameras into thinking that they see for instance a highway guardrail, rather than the tank hidden beneath the cloak.

Photos: Hongrui Jiang / University of Wisconsin-Madison