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NEWS
New Cloaking Material Renders Hot Objects Practically Invisible
June 27, 2018

Infrared cameras are the heat-sensing eyes that help drones find their targets even in the dead of night or through heavy fog.

Hiding from such detectors could become much easier, thanks to a new cloaking material that renders objects – and people – practically invisible.


A newly developed stealth sheet can hide hot objects like human bodies or military vehicles from infrared cameras. Photo: Hongrui Jiang

“What we have shown is an ultrathin stealth ‘sheet.’ Right now, what people have is much heavier metal armor or thermal blankets,” says Hongrui Jiang, professor of electrical and computer engineering at the University of Wisconsin-Madison (UW-Madison).

Warm objects like human bodies or tank engines emit heat as infrared light. The new stealth sheet, described recently in the research journal Advanced Engineering Materials, offers substantial improvements over other heat-masking technologies.

According to information, less than one millimeter thick, the sheet absorbs approximately 94 percent of the infrared light it encounters. Trapping so much light means that warm objects beneath the cloaking material become almost completely invisible to infrared detectors.

To trap infrared light, Prof. Jiang and colleagues turned to a unique material called black silicon, which is commonly incorporated into solar cells. Black silicon absorbs light because it consists of millions of microscopic needles (called 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.

Although black silicon has long been known to absorb visible light, Prof. Jiang and colleagues were the first to see the material’s potential for trapping infrared. They boosted its absorptive properties by tweaking the method through which they created their material.

“We didn’t completely reinvent the whole process, but we did extend the process to much taller nanowires,” says Prof. Jiang, who developed the material in National Science Foundation-supported facilities at UW-Madison.

Prof. Jiang and colleagues are working to scale up their prototype for real-world applications with assistance from UW-Madison’s Discovery to Product program. They received a U.S. patent in the fall for the material’s use in stealth. The Wisconsin Alumni Research Foundation supported the research through its Robert Draper Technology Innovation Fund, and is actively pursuing two additional patent applications.


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