Stretchable skin cloaks objects by trapping radar waves

March 08, 2016 // By Jean-Pierre Joosting
A flexible, stretchable and tunable "meta-skin" that uses rows of small, liquid-metal devices to cloak an object from the sharp eyes of radar has been developed by Iowa State University engineers. The metamaterial can be tuned to reduce the reflection of a wide range of radar frequencies by controlling the stretching and flexing of the polymer meta-skin.

"It is believed that the present meta-skin technology will find many applications in electromagnetic frequency tuning, shielding and scattering suppression," the engineers wrote in their paper, published in the journal Scientific Reports.

To prove the idea that electromagnetic waves — and perhaps even the shorter wavelengths of visible light — can be suppressed with flexible, tunable liquid-metal technologies, the researchers implemented rows of split ring resonators embedded inside layers of silicone sheets. The electric resonators are filled with galinstan, a metal alloy that's liquid at room temperature and less toxic than other liquid metals such as mercury.

Those resonators are small rings with an outer radius of 2.5 millimeters and a thickness of half a millimeter. They have a 1 millimeter gap, essentially creating a small, curved segment of liquid wire.

The rings create electric inductors and the gaps create electric capacitors. Together they create a resonator that can trap and suppress radar waves at a certain frequency. Stretching the meta-skin changes the size of the liquid metal rings inside and changes the frequency the devices suppress.

Tests showed radar suppression was about 75 percent in the frequency range of 8 to 10 gigahertz, according to the paper. When objects are wrapped in the meta-skin, the radar waves are suppressed in all incident directions and observation angles.

According to the paper this meta-skin technology is different from traditional stealth technologies that often only reduce the backscattering (the power reflected back to a probing radar).

"The long-term goal is to shrink the size of these devices," said Dong, one of the lead authors. "Then hopefully we can do this with higher-frequency electromagnetic waves such as visible or infrared light. While that would require advanced nanomanufacturing technologies and appropriate structural modifications, we think this study proves the concept of frequency tuning and broadening, and multidirectional wave suppression with skin-type metamaterials."

Lead authors from Iowa State's department of electrical and computer engineering are