New 'illusion coating' hides objects from detection

Researchers have developed a new 'illusion coating' that could hide things by making them look like something else or even completely disappear.
"Previous attempts at cloaking using a single meta-surface layer were restricted to very small-sized objects," said Zhi Hao Jiang, postdoctoral fellow in electrical engineering, Pennsylvania State University.
Jiang and Douglas H Werner developed a meta-material coating with a negligible thickness that allows coated objects to function normally while appearing as something other than what they really are, or even completely disappearing.
The researchers employ what they call "illusion coatings," coatings made up of a thin flexible substrate with copper patterns designed to create the desired result.

They can take a practical size metal antenna or sensor, coat it with the patterned film and when the device is probed by a radio frequency source, the scattering signature of the enclosed object will appear to be that of a prescribed dielectric material like silicon or Teflon.
Conversely, with the proper pattern, they can coat a dielectric and it will scatter electromagnetic waves the same as if it were a metal object.

"The demonstrated illusion/cloaking coating is a lightweight two-dimensional meta-surface, not a bulky three-dimensional meta-material," said Werner.
The researchers take the object they want cloaked and surround it with a spacer, either air or foam.

They then apply the ultra-thin layer of dielectric with copper patterning designed for the wavelengths they wish to cloak. In this way, antennae and sensors could be made invisible or deceptive to remote inspection.
Another application of this material would be to protect objects from other emitting objects nearby while still allowing electromagnetic communication between them.
This was not possible with the conventional transformation optics-based cloaking method because the cloaking mechanism electromagnetically blocked the cloaked object from the outside, but this new coating allows the object surrounded to continue working while being protected.
In an array of antennae, for example, interference from the nearby antennas can be suppressed.

The meta-surface coating consists of a series of copper, geometric patterns placed on a flexible substrate using standard lithographic methods currently used to create printed circuit boards.
Each illusion coating must be designed for the specific application, but the designs are optimised mathematically. This method of manufacture is low cost and well established.
The research was published in the journal Advanced Functional Materials.