'Illusion coatings' are like futuristic camouflage

An antenna covered with an illusion coating, making it appear to be something entirely different. (Zhihao Jiang/Penn State)

Instead of using invisibility cloaks to conceal objects from detection, "illusion coatings" could hide things by making them look like something else, researchers say.

These illusion coatings could help soldiers or spies hide antennas and sensors from remote inspection while still allowing the devices to scan the outside world, the scientists added.

Invisibility cloaks, once thought of only as "Star Trek" science fiction or "Harry Potter" fantasy, work by smoothly guiding light waves around objects so the waves ripple along their original paths as if nothing were there to block them. Cloaking devices that work against other kinds of waves are possible as well, such as the acoustic waves used in sonar. [Science Fact or Fiction? The Plausibility of 10 Sci-Fi Concepts]

But one problem with invisibility cloaks is that they isolate whatever they enclose. This means "the act of cloaking would prevent an enclosed antenna or sensor from communicating with the outside world," lead study author Zhi Hao Jiang, an electrical engineer at Pennsylvania State, said in a statement.

Instead, scientists have now developed what they call illusion coatings flexible, lightweight materials that can make whatever they cover appear to be something other than what they really are.

The investigators started with thin sheets of a composite material composed of glass fibers and Teflon. These were covered with patterns of copper stripes that interacted with the composite material to scatter radio waves in a very precise way. The stripes are only 35 microns deep and about 300 to 500 microns wide. (For comparison, the average width of a human hair is 100 microns.)

Next, the researchers took whatever they want cloaked and surrounded it with a separator either air or foam. Finally, they applied the coating. Depending on the copper patterns used, the researchers could make a copper antenna or sensor look like silicon or Teflon when it was scanned by radio waves. They could also make a Teflon cylinder look like a metal object.

These illusion coatings may one day help protect antennas and sensors from discovery by hostile forces. "The coatings we invented can still allow for the electromagnetic communication between the coated object and the outside world," said study co-author Douglas Werner, an electrical engineer at Pennsylvania State University. "A sensor will be electromagnetically hidden or camouflaged while it still maintains its sensing functionality."

Illusion coatings may also help protect any type of equipment from stray or intentional electromagnetic interference. For instance, they could help enable multiple-antenna arrays, "where each antenna will not be affected by the presence of the other antennas, even when they are placed in very close proximity to each other," Werner said.

In addition, illusion coatings could be used for tasks other than hiding. For example, they could help channel radio signals to improve telecommunications, Werner said.

While these illusion coatings currently only work for radio frequencies, the researchers are exploring ones that work against infrared and visible wavelengths of light, Werner said.

The scientists will present their work in January at a meeting of the Royal Society in Chicheley, England. The findings were detailed online Oct. 9 in the journal Advanced Functional Materials.

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