The chameleon effect
Talk about inspo. The chameleon, a lizard known for its color-changing skin, is the inspiration behind a new electromagnetic material that could someday make vehicles and aircraft “invisible” to radar. A team of engineers has developed a tunable metamaterial microwave absorber that can switch between absorbing, transmitting or reflecting microwaves on demand by mimicking the chameleon’s color-changing mechanism.
“A key discovery was the ability to achieve both broadband absorption and high transmission in a single structure, offering adaptability in dynamic environments,” said Grace Gu, assistant professor of mechanical engineering. “This flexibility has wide-ranging applications, from stealth technology to advanced communication systems and energy harvesting.”
Creating materials that can efficiently absorb electromagnetic waves, like radar or microwaves, has been a longstanding challenge. Seeking to create a material that could dynamically change how it interacts with electromagnetic waves, the researchers looked to the chameleon. The sticky-tongued reptile changes color by adjusting the spacing between photonic crystals in its skin to modulate light reflection.
Gu and her team worked to adapt a similar tuning mechanism to their metamaterial design. The result was a crisscross truss structure that can mechanically transform to control its electromagnetic properties. By collapsing or expanding — a synchronized movement enabled by the interlinked system of trusses — the metamaterial can vary its electromagnetic response from broadband absorption to transmission mode.
Using machine learning and genetic algorithms, the researchers optimized the structure’s design for specific, targeted electromagnetic responses, achieving a level of programmability. They then fabricated the structure using 3D printing and tested its ability to switch between absorbing and transmitting microwaves.
“In its collapsed form, the structure absorbs over 90% of microwaves in the 4–18 GHz range, effectively rendering it invisible to radar and achieving stealth,” said postdoctoral researcher Daniel Lim. “When expanded, it allows up to 24.2% signal transmission, enabling communication when needed.”
This bioinspired electromagnetic material has the potential to enhance technologies in a broad range of fields, including defense, wireless communications, energy and smart infrastructure. The material also could be used to create smart windows that switch between blocking and transmitting signals, or improve the efficiency of electromagnetic energy harvesting systems that help power sensors and batteries.
Co-authors include Alberto Ibarra and Jiyoung Jung from the Department of Mechanical Engineering, and Jeongwoo Lee and Wonjoon Choi from Korea University.
Learn more: New electromagnetic material draws inspiration from the color-shifting chameleon; A tunable metamaterial microwave absorber inspired by chameleon’s color-changing mechanism (Science Advances)