U.S. researchers say they've created a cloaking material that can render objects invisible in the terahertz range, which lies between infrared and microwaves.

Scientists at Northwestern University say the design can't translate into an invisibility cloak for the visible spectrum but it could have implications in diagnostics, security and communications, a university release said Wednesday.

The material, designed by Northwestern professor of mechanical engineering Chen Sun, uses microfabricated gradient-index materials to manipulate the reflection and refraction of light.

Humans normally recognize objects through two features -- shape and color. To render an object invisible, light must be manipulated so it will neither scatter at an object's surface nor be absorbed or reflected by it, the process that gives objects color.

Sun says the purpose of the cloak is not to hide items but to get a better understanding of how to design materials that can manipulate light propagation.

"This demonstrates that we have the freedom to design materials that can change the refraction index," Sun said. "By doing this we can manipulate light propagation much more effectively."

Sun says he has no plans to attempt to extend his invisibility 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."