KAIST Develops "Electromagnetic Wave Cloaking" Technology That Controls Radio Waves as It Stretches [Reading Science]

Realization of Stretchable Metamaterials with Liquid Metal Ink
Potential Applications in Wearables, Robotics, and Stealth Technology

The "cloaking technology," which manipulates electromagnetic waves to avoid detection by radar or sensors, has now been realized in the form of a flexible, stretchable material. Researchers at the Korea Advanced Institute of Science and Technology (KAIST) have developed a core, original technology for stretchable electromagnetic wave cloaking that can absorb and control electromagnetic waves even in environments with frequent deformation and movement.

On December 16, KAIST announced that the research teams led by Professor Hyungsu Kim of the Department of Mechanical Engineering and Professor Sanghoo Park of the Department of Nuclear and Quantum Engineering have developed next-generation stretchable metamaterial technology capable of absorbing, controlling, and shielding electromagnetic waves, based on "liquid metal composite ink" (LMCP). Electromagnetic wave cloaking technology refers to controlling the reflection and absorption of electromagnetic waves so that objects remain undetectable by radar or various sensors.

Cover of the October 2025 issue of the international academic journal Small, featuring the research paper as the cover article. Provided by KAIST

Conductivity Maintained Even When Stretched Up to 12 Times... Realization of "Stretchable Metamaterials"

To implement electromagnetic wave cloaking technology, it is essential to precisely control the flow of radio waves on the surface of an object. However, conventional metal materials are rigid and not easily stretchable, posing limitations for applications in wearable devices, robots, or flexible structures that frequently change shape.

The liquid metal composite ink developed by the research team maintains electrical conductivity even when stretched up to 12 times (1200%) its original length and demonstrates high stability, showing almost no oxidation or performance degradation even after prolonged exposure to air. It is characterized by its rubber-like flexibility while retaining the electrical properties of metal.

This property is possible because, during the drying process of the ink, the internal liquid metal particles spontaneously connect to form a mesh-like metallic network structure. The research team designed this structure as a metamaterial, using repetitive micro-patterns to control the electromagnetic wave response in the desired manner.

Photo of the research team. From the top row, left to right: Hyunseung Lee, PhD candidate; Wonho Choi, Professor. From the bottom row, left to right: Hyungsu Kim, Professor; Sanghoo Park, Professor; (top) First author Jungsu Pyeon, PhD. Provided by KAIST

World’s First Demonstration: Absorption Characteristics Change Depending on Degree of Stretching

The research team was the first in the world to fabricate a "stretchable metamaterial absorber" whose electromagnetic wave absorption characteristics vary depending on the degree of stretching, using this ink. After printing patterns with the ink and stretching them like a rubber band, they observed that the frequency band of the absorbed radio waves changed.

This means that, depending on the environment or situation, objects can be made less detectable by radar or communication signals more effectively. In particular, since the material can be produced simply by printing or coating and drying, without the need for high-temperature processing or laser machining, it offers significant advantages in terms of process simplicity and scalability.

This technology is regarded as a next-generation electronic material platform that simultaneously satisfies stretchability, conductivity, long-term stability, ease of processing, and electromagnetic wave control functionality. Potential applications include artificial skin for robots, skin-adhering wearable devices, and radar-evading technologies in the defense sector.

Professor Hyungsu Kim stated, "A major achievement is that electromagnetic wave functionality can be implemented solely through a printing process, without the need for complex equipment," adding, "We expect it to be applied in various fields, including robotics, wearable devices, and defense."

This research was published as the cover article in the October 2025 issue of the international academic journal Small. The title of the paper is "Versatile Liquid Metal Composite Inks for Printable, Durable, and Ultra-Stretchable Electronics." The study was supported by the National Research Foundation of Korea's Basic Research Program and the KAIST UP Program.