Engineers develop flexible skin that traps radar waves, cloaks objects

It’s a bird, it’s a plane, it’s…wait, I don’t see anything there. Stealth aircraft could get even harder to detect with a new flexible, stretchy metamaterial that effectively traps and suppresses radar waves.

The cloaking tech has potential military applications, including coating next-generation stealth bombers.

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A team at Iowa State University led by electrical and computer engineering professor Jiming Song and associate professor Liang Dong developed a metamaterial they’re calling “meta-skin.”

Metamaterials are manmade materials that have capabilities greater than the sum of their individual components. While cartoonist Randall Munroe sadly doesn’t have an entry for them in his “Thing Explainer” book, his xkcd comic strip does. Having learned about the physical feats some can pull off, I think they’re kind of magical.

The engineers at Iowa State University created their metamaterial by embedding rows of tiny split-ring resonators inside silicone sheets. These resonators contain the liquid metal alloy galinstan, which is gallium, indium, and tin. It’s used commercially and has low toxicity compared to other liquid metals. I even found some on Amazon.com.

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The meta-skin can be tuned to trap and suppress specific radar frequencies by stretching out the liquid metal rings, according to the university. When the team tested their metamaterial by wrapping it around a dielectric cylindrical rod at different angles, they found it did well and even reached a radar suppression of about 75 percent in the 8 to 10 gigahertz range.

According to the Physics Factbook, that band is used for civil marine radar, tracking radar, airborne weather avoidance radar, systems for detecting mortar and artillery projectiles, and police speed meters.

Despite repeated measurements, the meta-skin didn’t crack or show signs of fatigue, the team reports in the journal Scientific Reports. The engineers think their stretchy metamaterial could one day cover next-gen stealth aircraft. Such tech promises to make military aircraft even more hidden from detection than the B-2.

“The long-term goal is to shrink the size of these devices,” Dong said in a university press release. “Then hopefully we can do this with higher-frequency electromagnetic waves such as visible or infrared light.” That’s right. Visible light, the holy grail for cloaking materials.

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Over the past few years, we’ve seen incremental advancements in cloaking devices and materials. There was the biocompatible silk-based metamaterial for invisibility in the terahertz range. Plus, the neat light-manipulating lens system for seeing through objects and that ultrathin metamaterial that turned nanoscale objects into flat mirrors.

While the ultimate Harry Potter-style invisibility cloak remains elusive, engineers are getting better at hiding objects from detection. They’ve still got a long way to go, but when they finally succeed in making large objects truly invisible, don’t say you didn’t see it coming.