Prof. Park Sang-hoo's research team, along with Prof. Kim Hyeong-su of the Department of Mechanical Engineering, has developed a flexible "invisibility cloak" technology.
2025-12-18
<From left in the top row: PhD candidate Lee Hyeon-seung, Professor Choe Won-ho, (front row left) Professor Kim Hyeong-su, Professor Park Sang-hoo, and Dr. Pyeon Jeong-su, the top first author>
On the 16th, a research team led by Professor Kim Hyung-soo of the Department of Mechanical Engineering and Professor Park Sang-hoo of the Department of Nuclear and Quantum Engineering at our university announced that they have developed a core technology for next-generation stretchable cloaking* technology capable of absorbing, controlling, and shielding electromagnetic waves, based on Liquid Metal Composite Ink (LMCP).
*Cloaking: A technology that makes an object appear invisible to detection devices such as radar and sensors.
To implement cloaking technology, the ability to freely control light or radio waves on the surface of an object is crucial. However, existing metal materials are rigid and inelastic,
and can easily break if forced to stretch. This has made their application in body-worn electronic devices and flexible robots challenging.
The liquid metal composite ink developed by the research team can be stretched up to 12 times (1200%) its original length without losing electrical power. It also exhibits high stability, showing little rust or performance degradation even after nearly a year in air. Unlike conventional metals, this ink is as flexible as rubber while retaining the properties of metal.
This property is possible because, as the ink dries, the liquid metal particles within it connect to each other, forming a mesh-like metallic network structure. This structure is a "metamaterial," an artificial structure created by repeatedly printing tiny patterns with ink so that radio waves react in a designed manner when they encounter the structure. The result is a material that is both as flexible as a liquid and as strong as a metal.
The fabrication process is also simple. Instead of complex processes like high-temperature baking or laser processing, the ink simply needs to be printed with a printer or brush and then dried.
Furthermore, the ink eliminates the unevenness and cracking that commonly occur when liquids dry, resulting in a smooth and uniform metallic pattern.
To demonstrate the performance of this ink, the research team created the world's first "stretchy metamaterial absorber," whose radio wave absorption properties change depending on the degree of stretching.
By simply printing the pattern with ink and stretching it like a rubber band, the type of radio wave (frequency band) absorbed changes. This suggests that, depending on the situation, it could lead to cloaking technology that can better conceal objects from radar or communication signals.
This technology is considered a groundbreaking electronic materials technology that simultaneously satisfies stretchability, conductivity, long-term stability, process simplicity, and electromagnetic wave control capabilities.
Professor Kim Hyung-soo stated, "We have now achieved electromagnetic wave functionality through a printing process alone, without complex equipment. This technology is expected to be utilized in a variety of future technologies, including robot skin, wearable devices, and radar stealth technology in the defense sector."
This research has been recognized as a key source technology in the field of next-generation electronic materials and was published on October 16, 2025, in the Wiley International Journal of Small, where it was selected as the cover paper.
※ Paper Title: J. Pyeon H. Lee, W. Choe, S. Park, H. Kim, "Versatile Liquid Metal Composite Inks for Printable, Durable, and Ultra-Stretchable Electronics," Small 2501829 (2025)
DOI: https://doi.org/10.1002/smll.202501829
※ Lead Author Information: First Author: Dr. Jeong-Soo Pyeon; Co-Authors: Ph.D. Candidate Hyun-Seung Lee and Professor Won-Ho Choe; Corresponding Authors: Professor Hyung-Soo Kim and Professor Sang-Hoo Park
This work was supported by the National Research Foundation of Korea (NRF) Individual Basic Research (MSIT: 2021R1A2C2007835) and the KAIST UP Program. <Selected Cover Paper for the October 2025 Issue of the International Journal of Small>
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