By Josh Perry, Editor
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Researchers at the University of Wisconsin (Madison, Wisc.) have created an ultra-thin sheet (less than one millimeter thick) that absorbs 94 percent of infrared light, masking warm objects that lie beneath it and making objects invisible to infrared detectors.

A newly developed stealth sheet can hide hot objects like human bodies or military vehicles from infrared cameras. (Hongrui Jiang/University of Wisconsin)

According to a report from the university, then sheet absorbs light in the mid- and long-wavelength infrared range, which is the temperature range of the human body. Adding electronic heating elements to the sheet created a high-tech disguise to trick cameras.

“To trap infrared light, [researchers] turned to a unique material called black silicon, which is commonly incorporated into solar cells,” the article explained. “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.”

The black silicon was boosted by creating taller nanowires in the production process. Tiny particles of silver are used to etch a layer of silicon, creating “a thicket of tall needles.” Researchers also added air channels into a flexible backing material, which prevents the sheet from heating too quickly as it absorbs infrared light.

The research was recently published in Advanced Engineering Materials. The abstract stated:

“To effectively hide objects and render them invisible to thermographic detectors, their thermal signatures in the infrared (IR) region of the spectrum may be concealed. However, to conceal broadband spontaneous thermal emission of objects, covering the mid? and long?IR is a major obstacle.

“Here, metallic?dielectric nanostructures and microscale IR emitters are integrated and transferred onto thin flexible substrates to realize IR stealth sheets. The nanostructures absorb and scatter a broad band of IR wavelengths to reduce both reflection and transmission to below 5% across a wide range from 2.5 to 15.5 μm, and thus significantly attenuate the amount of IR signals propagating toward the detectors.

“Results show that the nanostructures with their unique properties can almost completely conceal the thermal emission from objects and blend them into their surroundings. In addition, micro?emitters thermally isolated from the broadband absorbers can present false thermography to deceive IR detectors and heat?sensing cameras.”