Revolutionary Electromagnetic Material Inspired by the Color-Changing Marvel of Chameleons

January 15, 2025 by Marni Ellery

Let’s talk about inspiration. The chameleon, a reptile recognized for its color-altering skin, serves as the foundation for a new electromagnetic material that could one day render vehicles and aircraft “invisible” to radar.

As reported today in the journal Science Advances, a group of engineers from UC Berkeley has created a tunable metamaterial microwave absorber capable of switching between absorbing, transmitting, or reflecting microwaves at will by imitating the color-changing mechanism of the chameleon.

“A significant finding was the ability to achieve both broadband absorption and high transmission within a single framework, providing adaptability in dynamic settings,” stated Grace Gu, the principal investigator of the research and an assistant professor of mechanical engineering. “This versatility has extensive applications, ranging from stealth technology to advanced communication systems and energy harvesting.”

Gu noted that the creation of materials that efficiently absorb electromagnetic waves, such as radar or microwaves, has been an enduring technological hurdle. “Current materials generally follow a ‘one-size-fits-all’ design,” she remarked. “Once created, they are limited in their response, which restricts their use in changeable environments where adaptability is essential.”

In pursuit of developing a material capable of dynamically altering its interaction with electromagnetic waves, the researchers drew inspiration from the chameleon. This sticky-tongued creature alters its color by changing the spacing between photonic crystals in its skin to affect light reflection.

Gu and her colleagues endeavored to adapt a similar tuning method to their metamaterial design. The outcome was a cross-braced truss structure able to mechanically adjust in order to control its electromagnetic characteristics. By contracting or extending — a coordinated movement facilitated by the interconnected system of trusses — the metamaterial can transition its electromagnetic response from broadband absorption to transmission mode.

Image representing the chameleon’s color-altering mechanism (above) and the bioinspired tunable metamaterial microwave absorber (below). (Image courtesy of the researchers)

Employing machine learning and genetic algorithms, the research team enhanced the structure’s design for specific, targeted electromagnetic reactions, achieving a degree of programmability. They subsequently manufactured the structure utilizing 3D printing and assessed its capacity to alternate between absorbing and transmitting microwaves.

“In its contracted form, the structure absorbs over 90% of microwaves within the 4–18 GHz spectrum, effectively becoming invisible to radar and achieving stealth,” explained Daniel Lim, postdoctoral researcher and primary author of the study. “When expanded, it permits up to 24.2% signal transmission, facilitating communication when necessary.”

Diagram illustrating the tuning of electromagnetic waves (microwaves) through the structural transformation of the metamaterial. (Image courtesy of the researchers)

As per Lim, this bio-inspired electromagnetic material possesses the capability to enhance technologies across a wide array of sectors, including defense, wireless communications, energy, and smart infrastructure.

“In defense scenarios, this adaptable metamaterial could facilitate the creation of vehicles or aircraft that can become ‘invisible’ to radar whenever necessary,” stated Lim. “Simultaneously, it can enable communication signals to permeate when needed, delivering both stealth and connectivity within a solitary system.”

This material could also serve in the development of smart windows that alternate between obstructing and transmitting signals, enhancing privacy and communication.

security. Furthermore, Gu envisions utilizing it to enhance the effectiveness of electromagnetic energy harvesting systems that assist in powering sensors and batteries.

“The adjustable quality of the design enables it to respond to evolving requirements, offering a flexible answer for electromagnetic wave regulation,” stated Gu.

Illustration of the mechanical actuation and shifting electromagnetic response of the arrayed structure. (Image credited to the researchers)

Among the co-authors of this research are Alberto Ibarra and Jiyoung Jung from UC Berkeley’s Department of Mechanical Engineering, as well as Jeongwoo Lee and Wonjoon Choi from Korea University’s School of Mechanical Engineering in Seoul.

This study received support from the Bakar Foundation, the Alfred P. Sloan Foundation, the National Science Foundation’s ACCESS supercomputing program, and UC Berkeley’s Molecular Graphics and Computation Facility.