PORTLAND, Ore. -- Invisibility cloaks began in the microwave regime using arrays of metamaterials to bend light around an object, thereby rendering it invisible to microwaves. While useful for hiding missiles and the like from radar, no one -- until now -- has successfully made one work like Harry Potter's to cloak people in the visible spectrum of light.
Now one lab, proving the concept with microwaves, has used an inexpensive 3D printer to make their cloak, which it claims can be extended to the visible spectrum. And a second lab, reporting on the same day, has used ordinary lens to achieve a cloaking effect at visible wavelengths.
"We are working on solving some of the fundamental challenges to metamaterials and our results may help in future invisible cloak development," professor Hao Xin and the University of Arizona.
Invisibility cloaks using active components instead of just passive metamaterials, promise to downsize their size to cloak even individual people.
(Source: Arizona University)
Other researchers working on the problem have merely used passive metamaterials to construct their invisibility cloaks, but the Arizona research group has incorporated active semiconductors -- battery-powered tunnel diodes -- into their 3D printed cloaks.
Xin's 3D printer proved the concept by making metamaterials from metals, plastics and other proprietary substances to create porous plastic balls with tiny copper wire circuit boards. When configured in a precise geometrical pattern they bend waves around objects using negative refraction.
University of Rochester researcher cloak using a special lens--the first invisibility cloak to work in the visible spectrum, according to the researchers.
(Source: Adam Fenster, University of Rochester)
"We incorporated active semiconductor devices into the passive structures that can compensate loss, even provide gain, potentially broaden the bandwidth as well as provide additional degree of freedom in design" Xin told us.
So far Xin has built small prototypes on his 3D printer using only a few metamaterial cells with gain. Xin's next step in his research is study how to use gain to increase the number of cells to cloak larger objects and eventually to build real applications.
"We eventually want build large scale objects using this technique. One challenge is to guarantee the stability of this kind of metamaterials, especially for larger scale objects using 100s or more unit cells," Xin told us. "We would like to explore increasing the bandwidth of this kind of metamaterial."
Beside merely cloaking objects for the United States Department of Defense, Xin hopes to build applications in other fields. "We would like to find realistic applications and implement them,"Xin told us. "Examples include compact and high performance antennas, biomedical imaging devices, and many others related to wireless communication and sensing."
Xin's predicts that he will achieve visible wavelength invisibility cloaks within his lifetime. His research was funded by the Air Force Office of Scientific Research.
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