Typically, to hide heat-radiating objects from infrared sensors—such as targets of drone or missile strikes—the military has used heavy metal armor or thermal blankets, which are bulky and impractical. To solve this problem, researchers at the University of Wisconsin-Madison (UW-Madison) have developed a new, ultra-thin cloaking material using black silicon that hides objects from infrared detectors just as effectively.
A team led by Professor Hongrui Jiang in UW-Madison’s College of Engineering has developed the material. He described it as an “ultra-thin stealth sheet” that can render people and objects invisible from infrared detectors.
A newly developed stealth sheet developed by researchers at the University of Wisconsin-Madison (UW-Madison) made from black silicon can hide hot objects like human bodies or military vehicles from infrared cameras. (Image source: Hongrui Jiang, UW-Madison)
“There has been lots of interest in an invisibility cloak in the visible light spectra and microwave spectra,” Jiang told Design News. However, there hasn’t been much exploration into creating stealth materials for the wide infrared spectra. “Current methods using metal sheets or linings or thermal blankets are heavy, high-cost, and have many drawbacks,” Jiang said.
The material he and his team created is less than one millimeter thick and absorbs about 94 percent of the infrared light it encounters. As a result, warm objects beneath the cloaking material become almost completely invisible to infrared detectors.
Key to the material’s functionality is that it can strongly absorb light in the so-called mid- and long-wavelength infrared range, the type of light emitted by objects at approximately human body temperature.
“[The material is] an ultra-thin sheet with black-silicon nanowires and silver nanoparticles to absorb infrared, with very low reflection and transmission,” Jiang explained. “Therefore, the sheet can effectively block the infrared emission, thus hiding the thermal signature of an object, such as a human body or an engine.”
The material also has an additional cloaking method in the form of air channels at the back of the sheets. They dissipate heat and electronics to generate a false heat signature as a disguise, presenting to the infrared camera a different object than the original one, Jiang said.
The black silicon used in the sheets is a unique material often used in solar cells. It absorbs light using nanowires that point upward like spires, which causes incoming light to reflect back and forth between the spires and bounce around rather than escape.
Although black silicon has long been known to absorb visible light, Jiang said he and his colleagues were the first to see the material’s potential for trapping infrared, boosting 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,” he explained.
Researchers believe that the military and law-enforcement agencies can use their material to hide people and objects from infrared sensors. They plan to continue their work to create a process to scale up production of the material for manufacturing, Jiang said.
The researchers published a paper on their work in the journal Advanced Engineering Materials.
Elizabeth Montalbano is a freelance writer who has written about technology and culture for 20 years. She has lived and worked as a professional journalist in Phoenix, San Francisco, and New York City. In her free time, she enjoys surfing, traveling, music, yoga, and cooking. She currently resides in a village on the southwest coast of Portugal.
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