KAIST, ‘Better Concealment the More It Moves’… ‘Invisible Cloak’ Realized with Stretchable Cloaking Technology

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Liquid Metal Ink Developed to Maintain Conductivity Even When Stretched Up to 12 Times… Expansion to Wearable Electronics, Robotics, and Stealth Technology

A KAIST research team has developed core fundamental technology for stretchable cloaking that can more effectively conceal electromagnetic waves the more it stretches and moves. Professor Hyung-soo Kim of the Department of Mechanical Engineering and Professor Sang-hoo Park of the Department of Nuclear and Quantum Engineering implemented a new concept of electronic material based on Liquid Metal Composite Ink (LMCP) that can absorb, control, and shield electromagnetic waves. This advancement goes beyond existing static concealment technologies, suggesting a technical progression closer to a ‘moving invisible cloak.’

Cloaking technology is a technique that makes an object appear absent to radar or sensors even though it exists, requiring the ability to freely control light or radio waves on the object’s surface. However, conventional metal materials were rigid and lacked stretchability, suffering from a rapid drop in electrical performance upon deformation. The research team overcame these limitations with a composite structure of liquid metal and polymer.

The LMCP ink developed by the team maintained its electrical conductivity even when stretched up to 12 times its original length, and showed virtually no oxidation or performance degradation even after being exposed to air for nearly a year. Thanks to a structure where the internal liquid metal particles self-form a metallic network during the drying process, the ink possesses both the flexibility of rubber and the function of metal simultaneously.

The manufacturing process is also simple. Uniform metal patterns can be realized merely by printing or applying with a brush and then drying, without high-temperature sintering or laser processing, making it suitable for large-area and mass production. These characteristics are evaluated as simultaneously solving the problems of process complexity and durability that have hindered the practical application of stretchable electronic materials.

Using the LMCP ink, the research team implemented the world’s first ‘stretchable metamaterial absorber’ whose absorbed frequency band of radio waves changes according to the degree of stretching. This structure, which alters its electromagnetic wave response characteristics simply by being stretched like a rubber band, shows that it can lead to cloaking technology that can more effectively hide an object from radar and communication signals depending on the situation.

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This electronic material simultaneously satisfies stretchability, conductivity, long-term stability, processing simplicity, and electromagnetic wave control, suggesting the potential for expansion into various fields such as wearable devices, transformable robots, and next-generation stealth technology.

Professor Hyung-soo Kim emphasized the ability to realize electromagnetic wave functions through a printing process without complex equipment, anticipating that this technology will lead to future applications such as robot skin, body-attached wearable devices, and radar stealth technology in the defense sector.

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