This flexible, stretchable and tunable ‘meta-skin’ can trap radar waves and cloak objects to prevent detection. Photo: Liang Dong/Iowa State University.
This flexible, stretchable and tunable ‘meta-skin’ can trap radar waves and cloak objects to prevent detection. Photo: Liang Dong/Iowa State University.

Engineers from Iowa State University have developed a new flexible, stretchable and tunable ‘meta-skin’ that uses rows of small, liquid-metal devices to cloak an object from the sharp eyes of radar.

The meta-skin takes its name from metamaterials, which are composites with properties not found in nature that allow them to 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.

This work is reported in a paper in Scientific Reports; the lead authors of the paper are Liang Dong and Jiming Song from Iowa State's department of electrical and computer engineering. The National Science Foundation and the China Scholarship Council partially supported the project.

"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.

Dong has a background in fabricating micro and nanoscale devices and working with liquids and polymers; Song has expertise in looking for new applications of electromagnetic waves. Working together, they were hoping to prove an idea: that electromagnetic waves – perhaps even the shorter wavelengths of visible light – can be suppressed using flexible, tunable liquid-metal technologies.

What they came up with are 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. These resonators comprise small rings with an outer radius of 2.5mm and a thickness of 0.5mm, with a 1mm gap at the bottom of each ring, 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 and thus the frequency that the resonator suppresses.

Tests showed that radar suppression was about 75% in the frequency range of 8–10 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.

According to Song, the meta-skin could coat the surface of the next generation of stealth aircraft. But the researchers are hoping for even more – a cloak of invisibility.

"The long-term goal is to shrink the size of these devices," Dong said. "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."

This story is adapted from material from Iowa State University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.