A domestic research team has developed a smart, transparent cloak-like technology that can hide electromagnetic waves better as it stretches and moves. It is expected to open new possibilities for moving robots, skin-mounted wearable devices, and next-generation stealth technology.
On the 16th, a research team led by Kim Hyeong-su, a professor in the Department of Mechanical Engineering at KAIST, and Park Sang-hu, a professor in the Department of Nuclear and Quantum Engineering at KAIST, said they developed a core source technology for next-generation composite cloaking based on liquid metal composite ink (LMCP) that can absorb, control, and shield electromagnetic waves.
Cloaking is a technology that makes an object appear absent to detection equipment such as radars or sensors, even when it is present. To implement this, light or radio waves on the object's surface must be freely controlled. However, existing metal materials are rigid and not very stretchable, and they easily break when forced to stretch. This created major challenges in applying the technology to skin-conforming electronic devices or robots that freely change shape.
The team developed a liquid metal composite ink that does not lose electrical conductivity even when stretched up to 12 times its original length and hardly rusts or degrades in performance even after being left in air for nearly a year. Unlike conventional metals, this ink is as soft as rubber while fully retaining the functions of a metal.
These characteristics are possible because, as the ink dries, the liquid metal particles inside interconnect and form a self-assembled metal network structure like a mesh. This structure is a "metamaterial," an artificial structure that makes radio waves respond in a designed way when they encounter the structure by repeatedly printing very small patterns with the ink. As a result, it simultaneously gains the properties of being as flexible as a liquid and as robust as a metal.
To validate the ink's performance, the team produced the world's first "stretchable metamaterial absorber," whose wave-absorbing properties change depending on how much it is stretched. After printing patterns with the ink, simply stretching it like a rubber band changed the types (frequency bands) of radio waves it absorbed. This shows it could lead to cloaking technology that hides objects better from radar or communication signals depending on the situation.
The material developed this time is also simple to make. Without complex processes such as high-temperature baking or laser machining, it only needs to be printed with a printer or brushed on and then dried. It also avoids common issues such as stains or cracking when drying liquids, enabling smooth and uniform metal patterns.
Professor Kim Hyeong-su said, "We can now implement electromagnetic functions with printing alone, without complex equipment," and noted, "This technology is expected to be used in a range of future technologies, including robotic skin, skin-mounted wearable devices, and radar stealth technology in defense."
This study was published in the international journal "Small" on Oct. and was also selected as a cover article.
References
Small(2025), DOI: https://doi.org/10.1002/smll.202501829