Invisibility cloaks, first demonstrated in complex lab experiments at Duke University seven years ago, could become much simpler to create using 3-D printing, a Duke engineer believes. "I would argue that essentially anyone who can spend a couple thousand dollars on a nonindustry-grade 3-D printer can literally make a plastic cloak overnight," said Yaroslav Urzhumov, assistant research professor in electrical and computer engineering at Duke's Pratt School of Engineering. Duke's Yaroslav Urzhumov holds the Frisbee-like invisibility cloak prototype created using a 3-D printer. Courtesy of Duke University Photography. In 3-D printing, or stereolithographic fabrication, a computer-guided nozzle lays down successive thin layers of a material — usually a polymer plastic — until a 3-D object is produced. Urzhumov said producing a cloak this way is inexpensive and easy: He and his team made a small one that resembles a Frisbee made out of Swiss cheese. Algorithms determine the location, size and shape of the holes to deflect microwave beams, and the fabrication process takes from three to seven hours. As with the 2006 cloak, the newer version deflects microwave beams, but researchers feel confident that, in the not-so-distant future, the cloak can work for higher wavelengths, including visible light. "We believe this approach is a way towards optical cloaking, including visible and infrared," Urzhumov said. "And nanotechnology is available to make these cloaks from transparent polymers or glass. The properties of transparent polymers and glasses are not that different from what we have in our polymer at microwave frequencies." The disklike cloak has an open area in its center where the researchers placed an opaque object. When microwave beams were aimed at the object through the side of the disk, the cloak made it appear that the object was not there. "The design of the cloak eliminates the 'shadow' that would be cast and suppresses the scattering from the object that would be expected," Urzhumov said. "In effect, the bright, highly reflective object, like a metal cylinder, is made invisible. The microwaves are carefully guided by a thin dielectric shell and then reradiated back into free space on the shadow side of the cloak." In theory, the technique can be used to create much larger devices, he said. "Computer simulations make me believe that it is possible to create a similar polymer-based cloaking layer as thin as one inch, wrapped around a massive object several meters in diameter. I have run some simulations that seem to confirm this point," he said. Other members of the team included Duke's Nathan Landy and David R. Smith, as well as Tom Driscoll and Dimitri Basov of the University of California, San Diego. The results were published online May 3 in Optics Letters doi 10.1364/OL.38.001606, and the work was supported by the US Army Research Office through a Multidisciplinary University Research Initiative grant.