Bioinspired metasurfaces act as thermal cloaks to infrared sensors

We tend to overlook how tiny particles—often dismissed as minor—can control color, light, and heat at macroscopic levels. This contradiction inspired Mady Elbahri, a professor of nanochemistry and nanoengineering at Aalto University in Finland to engineer a “nanocloud” out of white plasmonic metasurfaces that dynamically tunes its color and temperature like a real cloud—between cooling white and heating grey. It remains “cloaked” to infrared (IR) sensors or thermal cameras, thanks to its low mid-IR emissivity.

These metasurfaces scatter sunlight via disordered metallic nanostructures that minimize thermal emission. This grey surface gets hot like black materials, but an important difference is that it doesn’t emit IR light.

As you might guess, these metasurface nanoclouds show potential for a wide range of climate and military applications such as adaptive coatings, radiative cooling, thermal heating, and thermal cloaking.

Mimic clouds

To create their nanoclouds, Elbahri and his team mimic clouds using a white metasurface of hemispherical particles over metal to enable strong backscattering within the visible-near infrared (NIR) and low emissivity within the thermal IR—for cooling and camouflage/cloaking. Then, by embedding tiny copper nanoparticles inside aluminum oxide, they created a polarizonic layer to absorb/reflect light and cancel backscattering by mimicking a grey cloud.

“It relies on broadband backscattering of the plasmonic white metasurface, and the directional radiation (specular reflection) of the polarizonic layer by collective resonant displacement of bound electrons—not free ones,” explains Elbahri. “This polarizonic layer suppresses scattering of the cloud, traps light, and raises surface temperature dramatically—up to 75°C, which surpasses even black absorbers.”

What do these metasurfaces enable? Dual-mode thermal control while appearing cloaked to thermal cameras. They provide strong cooling when used alone, and powerful heating when combined with the team’s polarizonic layer. “We can switch between both without changing color or thickness—just by design,” Elbahri says.

Reimagining light-matter interaction

The biggest challenge “was to break free from the traditional scattering-vs.-absorption models,” Elbahri says. “Standard simulation tools and optical theories couldn’t capture the resonant, directional regime we observed. We had to rethink light-matter interaction at the sub-5-nm scale from first principles to uncover how these particles govern both color and thermal behavior, and then design experiments that can link these two domains. This concept is at the heart of our work.”

Next up for the team’s work: Dynamic coatings that use electrochromic or phase-changing layers for real-time, user-controlled switching between states.

As far as a timeline, the core concept is ready now for further experimental studies and proof-of-concept devices—particularly in thermal management, camouflage, and energy surfaces. “It felt like a real achievement to get these interesting results without dedicated funding, driven by confidence in the idea, curiosity, and determination,” says Elbahri. “We’re searching for partners and support to scale up our work to fully explore its real-world potential. The scientific foundation is solid, and now it’s about unlocking what comes next and pushing this to atmospheric science to understand real cloud and aerosol interactions from a materials perspective.”

FURTHER READING

M. Adel Assad et al., Adv. Mater. (Jun. 6, 2025); https://doi.org/10.1002/adma.202501080.