Engineering team finds way to make objects “invisible” to microwaves

A team led by Duke University’s Pratt School of Engineering demonstrate a cloak for deflecting microwaves in on October 19. According to the university’s press release, the “invisibility cloak” deflects microwave beams so they flow around a “hidden” object inside with little distortion, making it appear almost as if nothing were there at all.
Cloaks that render objects essentially invisible to microwaves could have a variety of wireless communications or radar applications, according to the researchers.
The team reported its findings on Thursday, Oct. 19, in Science Express, the advance online publication of the journal Science. The research was funded by the Intelligence Community Postdoctoral Fellowship Program.
The researchers manufactured the cloak using “metamaterials” precisely arranged in a series of concentric circles that confer specific electromagnetic properties. Metamaterials are artificial composites that can be made to interact with electromagnetic waves in ways that natural materials cannot reproduce.
The team produced the cloak according to electromagnetic specifications determined by a new design theory proposed by Sir John Pendry of Imperial College London, in collaboration with the Duke scientists. The cloak designer is David Schurig, a research associate in Duke’s electrical and computer engineering department.
“One first imagines a distortion in space similar to what would occur when pushing a pointed object through a piece of cloth, distorting, but not breaking, any threads,” Schurig said. “In such a space, light or other electromagnetic waves would be confined to the warped ‘threads’ and therefore could not interact with, or ‘see,’ objects placed inside the resulting hole.”
The researchers used a mathematical description of that concept to develop a blueprint for a cloak that mimics the properties of the imagined, warped space, he said.
“You cannot easily warp space, but you can achieve the same effect on electromagnetic fields using materials with the right response,” Schurig continued. “The required materials are quite complex, but can be implemented using metamaterial technology.”
In the case of the new cloak, that structure consists of copper rings and wires patterned onto sheets of fiberglass composite that are traditionally used in computer circuit boards.
To assess the cloak’s performance, the researchers aimed a microwave beam at a cloak situated between two metal plates inside a test chamber, and used a specialized detecting apparatus to measure the electromagnetic fields that developed both inside and outside the cloak. By examining an animated representation of the data, they found that the wave fronts of the beam separate and flow around the center of the cloak.
“The waves’ movement is similar to river water flowing around a smooth rock,” Schurig said.
Although the new cloak demonstrates the feasibility of the researchers’ design, the findings nevertheless represent a “baby step” on the road to actual applications for invisibility, said team member Steven Cummer, a professor of electrical and computer engineering at Duke.
The researchers said they plan to work toward developing a three-dimensional cloak and further perfecting the cloaking effect.
In an Associated Press report, Smith speculated that the technology might eventually be used to “cloak” acoustic waves so as to shield a region from vibration or seismic activity.
For more details or view a video, see http://dukenews.duke.edu/2006