When you hear of an “invisibility” material, perhaps you think of Harry Potter roaming the library undetected, wrapped in his magic cloak.
For engineering professor Alon Gorodetsky and his researchers, that kind of invisibility has not arrived. The University of California – Irvine (UCI) team, however, has found other ways to disappear.
To blend into their surroundings, cephalopods like the common squid change how they absorb and reflect light. The UCI-developed stretchy material, modeled after squid skin, achieves its thermal invisibility by reflecting heat.
Gorodetsky led the development of the adaptive camouflage materials that change their infrared reflectance on demand, enabling the surface to acquire desired – and potentially deceiving – thermal signatures when visualized under an infrared camera.
After being stretched or electrically triggered, the material’s thin swatches quickly change heat reflectance, smoothing or wrinkling their surfaces in under a second.
The modulation of apparent temperatures enables an invisibility to infrared night-vision tools.
“It goes from wrinkled and dull to smooth and shiny, essentially changing the way it reflects the heat,” said Gorodetsky of the material.
The UCI professor spoke to Tech Briefs about potential uses for thermal “invisibility,” including better camouflage, spacecraft insulation, and emergency shelters.
Tech Briefs: How does the material work?
Prof. Alon Gorodetsky: Essentially, you start out with a surface that's wrinkled. The wrinkles are tens to hundreds of microns scale, and then you flatten that surface. In those two states is where you have the differences in how the material reflects heat or infrared light.
Tech Briefs: What are the differences in how a “flattened” or “wrinkled” material reflects heat?
Gorodetsky: In the flattened state, the material reflects the heat right back at you. In the wrinkled state, the material scatters the heat, so it doesn't come right back at the source, or at a camera, that's looking at heat reflection.
Being able to go between those two states is what gives these adaptive properties to the material. When you look at that surface under an infrared camera, those two states will look very different and they'll have very different apparent temperatures. That effectively lets the material reappear and disappear under an infrared camera.
The material is primarily [designed] for thermal imaging. That's what we've focused on so far, so that material would let you match the apparent temperature of your background. Under a thermal camera, you would look like you have the same temperature [as the background], and you could change that on demand.
Tech Briefs: What inspired you to make this material?
Gorodetsky: We were really inspired by cephalopods, like squid, octopuses, and cuttlefish Specifically, we were inspired by their ability to blend into their background or to blend into their surroundings, to take on the appearance, texture, and color of objects near them.
Tech Briefs: What does the material look like?
Gorodetsky: In many ways, it looks like a shiny mirror or a sheet of aluminum foil. It's soft and conformable. It's essentially aluminum coated plastic, made of pretty common polymers, plastics, and metals or oxides. One of the polymers that we used happened to be a very good proton conductor, and so that helped us develop electrical strategies for changing the properties of the material.
Tech Briefs: Where do you see this technology being most valuable?
Gorodetsky: The camouflage aspect is one, for example, for security applications, but there are many common technologies that rely on controlling thermal radiation.
For example, you could create windows on buildings that in one state might reflect heat, but in another state might let it in to maintain the temperature of the building.
Let’s say you're a marathon runner and right at the end of your run; they're giving you these aluminum-coated sheets to wrap yourself in, so that you can trap all your radiated heat and stay warm as your body temperature drops.
One person might be really, really cold, and they might want to trap all their heat, and another person might not be as affected, and might want only a lighter covering that doesn't trap heat as well. You could imagine a technology like ours. In one state, it would trap all that heat; in another state, it would let that heat out.
Tech Briefs: What's most exciting to you about the possibilities for this kind of material?
Gorodetsky: I think the most exciting part is how many different aspects of people's daily lives it could impact if we could turn this into a manufacturable and low-cost technology. There are so many things that we use that rely on controlling infrared radiation: electronics, food container packaging, clothing, and energy conservation in buildings like rooftops and windows, for example. There's just a huge range of possibilities, and I think that opens up a very large playground of applications in the future.
What possibilities are you interested in? Share your questions and comments below.