Beautiful 3D-printed "metamaterial" sculptures that shrink when heated

Researchers from MIT and the University of Southern California 3D printed tiny, and quite beautiful, sculptures out of two different materials that usually expand when heated. But the specific architectures of these sugarcube-sized sculptures instead enable them to shrink when heated. The effect is similar to a Hoberman sphere, the wonderful isokinetic toy sculpture that mechanically collapses to a fraction of its original size. From MIT News:

The researchers consider the structures to be “metamaterials” — composite materials whose configurations exhibit strange, often counterintuitive properties that are not normally found in nature.

In some cases, these structures’ resistance to expanding when heated — rather than their shrinking response per se — may be especially useful. Such materials could find applications in computer chips, for example, which can warp and deform when heated for long periods of time. “Printed circuit boards can heat up when there’s a CPU running, and this sudden heating could affect their performance,” (MIT mechanical engineer Nicholas X.) Fang says. “So you really have to take great care in accounting for this thermal stress or shock..."

Fang and his colleagues printed small, three-dimensional, star-shaped structures made from interconnecting beams. They fabricated each beam from one of two ingredients: a stiff, slow-to-expand copper-containing material, and a more elastic, fast-expanding polymer substance. The internal beams were made from the elastic material, while the outer trusses were composed of stiff copper.

“If we have proper placement of these beams and lattices, then even if every individual component expands, because of the way they pull each other, the overall lattice could actually shrink,” Fang says...

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Cloaking device demonstrated

After years of research, "perfect" invisibility cloaks are finally a reality— at least so long as you are a tiny cylinder.

In 2006, the development of metamaterials resulted in a working example of a cloaking device, an essential accoutrement for young wizards and evil Klingon generals alike. Practical complexities, however, meant the material offered no more than a "simplifying approximation" of the desired functionality.

Now, however, researchers Nathan Landy and David R. Smith have described a "perfect" implementation in A full-parameter unidirectional metamaterial cloak for microwaves, a new study published by Nature: "Here, we design and experimentally characterize a two-dimensional, unidirectional cloak that makes no approximations to the underlying transformation optics formulation, yet is capable of reducing the scattering of an object ten wavelengths in size. We demonstrate that this approximation-free design regains the performance characteristics promised by transformation optics."

In other words, the cloaked object is completely invisible, unlike previous attempts in which reflections were visible: good enough for the Predator's interstellar hunting trips, but not for the Center for Metamaterials and Integrated Plasmonics in Durham, N.C.

While this is the first successful demonstration of the original 2006 paper's claims, that's not to say that there'll be practical implementations any time soon. The effect still only worked when viewed from one direction, and on a perfectly cylindrical object. Read the rest