Stretchy skin cloaks objects by trapping radar

This flexible, stretchable, and tunable "meta-skin" can trap radar waves and cloak objects from detection. (Credit: Liang Dong/Iowa State University)

A new flexible, stretchable and tunable “meta-skin” uses rows of liquid-metal devices to cloak an object from the sharp eyes of radar.

The meta-skin takes its name from metamaterials, which are composites that have properties not found in nature and that can manipulate electromagnetic waves. By stretching and flexing the polymer meta-skin, it can be tuned to reduce the reflection of a wide range of radar frequencies.

The new technology proves an idea: Electromagnetic waves—perhaps even the shorter wavelengths of visible light—can be suppressed with flexible, tunable liquid-metal technologies.

Jiming Song, a professor of electrical and computer engineering at Iowa State University, was a member of the team that developed the technology. He says the meta-skin could one day coat the surface of the next generation of stealth aircraft.

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But the researchers are hoping for even more: a cloak of invisibility.

“The long-term goal is to shrink the size of these devices,” says team member Liang Dong, an associate professor of electrical and computer engineering. “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.”

How it works

Rows of split ring resonators are 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.

“Therefore, this meta-skin technology is different from traditional stealth technologies that often only reduce the backscattering—i.e., the power reflected back to a probing radar,” the engineers wrote in their paper published in Scientific Reports.

Source: Iowa State University