Engineers at 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 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 journal Scientific Reports recently reported the discovery online. Lead authors from Iowa State’s department of electrical and computer engineering are Liang Dong, associate professor; and Jiming Song, professor. Co-authors are Iowa State graduate students Siming Yang, Peng Liu and Qiugu Wang; and former Iowa State undergraduate Mingda Yang. The National Science Foundation and the China Scholarship Council have partially supported the project.
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 with 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.
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.
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. This meta-skin could eventually coat the surface of the next generation of stealth aircraft.
"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 nano-manufacturing 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.”
