"Like Harry Potter's Invisibility Cloak": KAIST Develops Core Technology for Next-Generation Cloaking

A next-generation "cloaking" technology that could open new possibilities for stealth technology has been developed in South Korea. Cloaking refers to a technique that prevents detection of objects by devices such as radar or sensors. This technology is expected to be applied to moving robots, wearable devices, and stealth technology, similar to the invisibility cloak seen in movies like Harry Potter.

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 a core original technology for next-generation cloaking. This technology is based on Liquid Metal Composite Ink (LMCP), which can absorb, control, and shield electromagnetic waves.

Invisibility cloak technology image (AI generated). Provided by KAIST

Cloaking technology can be realized when light or electromagnetic waves can be freely controlled on the surface of an object. However, conventional metal materials are rigid and not very stretchable, and they tend to break easily when forcibly stretched. For this reason, they have not been applicable to electronic devices that are worn close to the body or to robots that change shape freely.

In contrast, the cloaking technology developed by the joint research team does not lose electrical conductivity even when stretched up to 12 times its original length. It also demonstrates high stability, as it does not rust or lose performance even after being stored in air for nearly a year. Most notably, unlike conventional metals, it retains the properties of metals while being as soft as rubber.

These characteristics are possible because, during the drying process of LMCP, the internal liquid metal particles connect with each other to form a self-assembled mesh-like metallic network structure.

This structure is a type of artificial material (metamaterial) created by repeatedly printing fine patterns with the ink, which causes electromagnetic waves to react "as designed" when they encounter the structure. Through this, the research team enabled LMCP to possess both the flexibility of a liquid and the robustness of a metal.

The manufacturing process is also simple. Without the need for complex processes such as high-temperature baking or laser processing, one can simply print or brush the ink and let it dry. When drying the liquid, there is no staining or cracking, making it possible to achieve smooth and uniform metallic patterns.

(Top row left) Hyunseung Lee, PhD candidate, Wonho Choi, Professor, (Second row left) Hyungsu Kim, Professor, Sanghoo Park, Professor, (Top) Jeongsu Pyeon, PhD, first author. Provided by KAIST

To demonstrate these capabilities, the joint research team produced the world's first "stretchable metamaterial absorber," whose electromagnetic wave absorption properties change depending on the degree of stretching.

When the LMCP pattern is stretched like a rubber band, the type of electromagnetic waves (frequency bands) it absorbs changes. This shows that, depending on the situation, the cloaking technology can better conceal objects from radar or communication signals.

This technology is evaluated as a groundbreaking electronic material that simultaneously satisfies stretchability, conductivity, long-term stability, process simplicity, and electromagnetic wave control capabilities.

Professor Kim said, "With LMCP, it is now possible to implement electromagnetic wave functions using only printing processes, without complex equipment. This technology is expected to be applied to a wide range of future technologies, including robot skin, wearable devices that adhere to the body, and radar stealth technology in the defense sector."

Meanwhile, this research has been recognized as an important original technology in the field of next-generation electronic materials. The research results (paper) were recently published in the international journal Small by Wiley and were also selected as the cover paper.