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Cloaking Coating Shows Visible Progress

Monday, October 20, 2014

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The quest for a cloak of invisibility may be one step closer to reality, with a new "illusion" coating taking shape at Pennsylvania State University.

Engineers there have developed a metamaterial, ultrathin coating that allows objects to function normally while appearing as something else, or even completely disappearing, according to an Oct. 13 research announcement.

Penn State campus
Penn State / Flickr

A team of engineers at Pennsylvania State University has developed so-called "illusion coatings."

Cloaking an object while maintaining its function is no small challenge.

“Previous attempts at cloaking using a single metasurface layer were restricted to very small-sized objects,” said Zhi Hao Jiang, postdoctoral fellow in electrical engineering. “Also, the act of cloaking would prevent an enclosed antenna or sensor from communicating with the outside world.”

Jiang and Douglas H. Werner, John L. and Genevieve H. McCain Chair Professor of Electrical Engineering at Penn State, recently reported their research in Advanced Functional Materials.

‘Illusion Coatings’

To create the illusion of invisibility, the researchers use something they call "illusion coatings." The coatings are made up of a thin, flexible substrate with copper patterns, the team said.

When used on a normal-sized metal antenna or sensor and probed by a radio frequency source, the scattering signature of the coated object appears similar to that of a dielectric material like silicon or Teflon, according to the engineers.

Zhihao Jiang
Zhihao Jiang / Penn State

The engineers covered an antenna with a copper patterned dielectric substrate to create a flexible metasurface that acts as an illusion coating.

Conversely, with the proper pattern, the team can coat a dielectric and make it scatter electromagnetic waves as if it were a metal object, the team reports.

"The demonstrated illusion/cloaking coating is a lightweight two-dimensional metasurface, not a bulky three-dimensional metamaterial," explained Werner.

How It Works

To make the antennae or sensor invisible or deceptive to remote inspection, the team uses an air or foam spacer around the object, then applies an ultrathin layer of dielectric with copper patterning designed for the wavelengths they wish to cloak.

The coating can also shield objects from nearby emitting objects while still allowing electromagnetic communication between them. For example, in an array of antennae, interference from nearby antennas can be suppressed, the team reports.

Conventional transformation optics-based cloaking does not permit this because the cloaking mechanism electromagnetically blocks the cloaked object from the outside, according to the researchers.


Manufacturing the new metasurface coating is low cost and well established, the team reports.

The series of copper, geometric patterns can be applied on a flexible substrate using standard lithographic methods now used to create printed circuit boards.

Penn State

Postdoctoral fellow Zhihao Jiang and Douglas H. Werner, professor of electrical engineering at Penn State, recently reported their research in Advanced Functional Materials.

Each illusion coating must be designed for the specific application, but the designs are optimized mathematically.

More Study Possible

Currently, the metasurface coatings work only on narrow bands of the spectrum for any application, but can be adapted to work in other bands of the electromagnetic spectrum, including the visible spectrum, the team said.

"We haven't tried expanding the bandwidth yet," said Werner. "But the theory suggests that it should be possible and it will probably require multiple layers with different patterns to do that."

The development could also improve the way radio frequency ID tags function.

The National Science Foundation supported the research.


Tagged categories: Coating Materials; Coatings technology; Engineers; North America; Research; Specialty functions

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