Autore: ExtremeTech

Harry Potter invisibility cloak

Researchers at the University of Texas in Austin have created a new, ultra-thin (0.15mm) Harry Potter-like invisibility cloak.

Until now, most invisibility cloaks have been large, cumbersome, desk-mounted constructions that really stretch the definition of the word cloak; for the most part, they’re more like proof of concepts for the invisibility material being tested, rather than actual invisibility cloaks. The University of Texas invisibility cloak, however, at just 166 micrometers thick, really is a cloak in the Harry Potter sense of the word.

Almost every invisibility cloak that we’ve written about, including the infamous Canadian camouflage/invisibility cloak, involves the use of metamaterials. Metamaterials are materials with properties that can’t be found in nature — usually, in the case of cloaking, materials that have a negative refractive index. A negative refractive index causes light to behave very oddly, allowing for the creation of superlenses that bend light beyond the diffraction limit, or cloaks that bend light in such a way as to make the covered object invisible. In this case, though, the researchers have eschewed metamaterials and instead fashioned an invisibility cloak out of conventional materials.

University of Texas, hiding a cylinder from microwaves with an invisibility cloakThe researchers created their invisibility cloak, dubbed a “metascreen,” out of a 66µm-thick sheet of copper that’s attached to a 100µm-thick sheet of flexible polycarbonate. This cloak is then attached to the object — in this case an 18cm (7in) cylinder — so that the cloak perfectly conforms to the object’s shape. The copper is patterned so that the scattered light from the cloak and the cloaked object cancel each other out. The end result is a cloak that hides the object from microwaves emitted from any direction, which might not sound all that impressive until you realize that most radar installations use microwaves.

In theory, the Texan metascreen could also be used to cloak visible light — after all, visible light, microwaves, and infrared are all physically identical; they’re just waves that oscillate at different frequencies. “In fact, metascreens are easier to realize at visible frequencies than bulk metamaterials and this concept could put us closer to a practical realization,” says Andrea Alu, co-author of the research paper. The one problem is that their patterned material scattering technique inversely scales with wavelength — so, while it’s possible to hide an 18cm cylinder from 3.6GHz microwave radiation, they can only hide micrometer-scale objects from 400-800THz visible light. One micrometer is 0.001 millimeters; the width of a red blood cell is about six micrometers.

Still, it’s yet another exciting invisibility cloak proof of concept. With the amount of money being poured into invisibility R&D, and the myriad of military (and consumer) uses, it’s really only a matter of time until an actual invisibility cloak is realized.

Now read: Physicists create world’s first multiverse of universes in the lab

Research paper: doi:10.1088/1367-2630/15/3/033037 - “Demonstration of an ultralow profile cloak for scattering suppression of a finite-length rod in free space”