Material that Vanishes when Shot with Microwave Energy

It's not quite the Invisible Man, but researchers say they have gotten
a step closer to creating a "three-dimensional cloak" that would
render objects invisible.

Scientists at the University of Texas in Austin today said they have
hidden a cylinder from microwaves, demonstrating cloaking of an object
in free space, rather than a two-dimensional image. The group has not
been able to scatter visible light, but it expects that cloaking small
objects is possible.

"Cloaking small objects may be exciting for a variety of applications.
For instance, we are currently investigating the application of these
concepts to cloak a microscope tip at optical frequencies. This may
greatly benefit biomedical and optical near-field measurements," said
University of Texas assistant professor Andrea Alu in a statement. He
is co-author of a paper published today in the Institute of Physics
and German Physical Society's New Journal of Physics.

Researchers for years have been designing synthetic materials to coat
an object and make it appear transparent. In its experiment, the
University of Texas group covered a cylinder with a shell coated with
a nanometer-sized plasmonic material that scatters light and other
electromagnetic waves.
When we see an object, our eyes receive the reflection of light rays
off that object and our brain processes that visual information. At
certain frequencies, plasmonic materials can excite electron
oscillations that make the light waves scatter in a way that
counteracts the normal reflection, according to the University of
Texas. The effect is to make it appear transparent.

The paper says that the plasmonic materials work regardless of the
shape of the object and, in principle, could work on a broader range
of frequencies, including visible light. But there appear to be some
limitations on what sorts of materials it will work on. The experiment
worked on a dielectric object but not on metals, according to a
description from the University of Texas.

In the future, though, portions of aircraft could be covered or
optical instruments could use the material to correct effects. "We
believe that our results pave the way to realistic, practical
applications of 3D stand-alone cloaks for radar evasion and
non-invasive radio frequency probing," according to the paper.