KAIST researchers develop new 'stealth cloak' to be applied to robots, wearable devices

A team of researchers at KAIST has developed a new liquid metal ink that could be applied to robots and wearable devices to absorb and block electromagnetic signals, making a stealth cloak.

The team, led by Prof. Kim Hyoung-soo of mechanical engineering along with Prof. Park Sang-hoo of nuclear and quantum engineering, developed a core technology for a next-generation stretchable cloaking system using a material called liquid metal composite ink (LMCP) that can absorb, control and block electromagnetic waves.

A key element of cloaking technology is to freely manipulate light or radio waves on the surface of an object. Conventional metal materials are rigid and not easily stretched, meaning they break when forcibly extended. This has made it difficult to apply cloaking to wearable electronics or shape-changing robots.

The liquid metal composite ink developed by the team can stretch up to 12 times its original length without losing conductivity, according to the team's research report. It also shows high long-term stability, resisting rust and performance degradation even after nearly a year in open air. Unlike typical metals, this ink is soft like rubber but retains the functional properties of metal.

This is possible because, as the ink dries, the liquid metal particles inside spontaneously form an interlinked, mesh-like network — a structure known as a "metamaterial." By printing the ink in tiny repeating patterns, researchers can design surfaces that respond to electromagnetic waves in specific ways. The ink can be applied and left to dry and does not need to be baked or processed in high temperatures.

To demonstrate its performance, the team created the world’s first "stretchable metamaterial absorber," a material that changes how it absorbs radio waves depending on how much it is stretched. The team said it could shift the frequencies of the electromagnetic waves the material absorbed by pulling on the patterned material like a rubber band — a sign that the material could dynamically adapt to better evade radar or communication signals, depending on its shape or movement.

“This technology makes it possible to implement electromagnetic functionality using only printing, without complicated equipment,” said Prof. Kim. “We expect it to be widely used in the future — in robotic skins, wearable electronics and radar stealth systems for defense applications.”

The research was recognized as a major advancement in next-generation electronic materials and was published as the cover article of the October 2025 issue of Small, an international journal by Wiley.

BY YOON SO-YEON [[email protected]]