11-08 :: August 2011

nanotimes News in Brief

Materials // Broadband Terahertz Invisibility Cloak

R

esearchers at Northwestern University have created a new kind of cloaking material that can

render objects invisible in the terahertz range. Though this design can’t translate into an invisibility cloak for the visible spectrum, it could have implications in diagnostics, security, and communication. The cloak uses microfabricated gradient-index materials to manipulate the reflection and refraction of light. In order to manipulate light in the terahertz frequency, which lies between infrared and microwaves, the research group develo- ped metamaterials. The tiny, prism-shaped cloaking structure, less than 10mm long, was created using a technique called electronic transfer microstereoli- thography, where researchers use a data projector to project an image on a liquid polymer, then use light to transform the liquid layer into a thin solid layer. Each of the prism’s 220 layers has tiny holes that are much smaller than terahertz wavelengths, which me- ans they can vary the refraction index of the light and render invisible anything located beneath a bump on the prism’s bottom surface; the light then appears to be reflected by a flat surface.

“This demonstrates that we have the freedom to de- sign materials that can change the refraction index,” Cheng Sun, assistant professor of mechanical engi- neering at Northwestern’s McCormick School of Engineering and Applied Science, said. “By doing

65

© Cheng Sun

this we can manipulate light propagation much more effectively.” Next Sun hopes to use what he’s learned through the cloak to create its opposite: a terahertz lens. He has no immediate plans to extend his invi- sibility cloak to visible frequencies. “That is still far away,” he said. “We’re focusing on one frequency range, and such a cloak would have to work across the entire spectrum.”

Fan Zhou, Yongjun Bao, Wei Cao, Colin T. Stuart, Jian- qiang Gu, Weili Zhang, Cheng Sun: Hiding a Realistic Object Using a Broadband Terahertz Invisibility Cloak, In: Scientific Reports, Vol. 1, September 2011, Article number: 78, DOI:10.1038/srep00078: http://dx.doi.org/10.1038/srep00078

http://www.mccormick.northwestern.edu/directory/ profiles/Cheng-Sun.html