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KIT's 'invisibility cloak' is set to inspire STEM students

01 May 2015

Invisibility cloaks that bend light around an object, shielding it from detection do exist but due to their limitations, rarely impress the average observer.

In a diffusive light-scattering medium, light moves olong random paths. A normal object casts a shadow, an object with an invisibility cloak does not (image: Robert Schittny/KIT)

Now, a group of researchers from the Karlsruhe Institute of Technology (KIT) has developed a portable invisibility cloak that can be taken into classrooms and used for demonstrations. It might not be able to hide a human, but it can make small objects disappear from sight without specialised equipment.

Scientists hoping to divert light around an object to render it invisible must find a way to compensate for the increased distance the light must now travel. To address this challenge, the KIT team constructed their cloak from a light-scattering material. By scattering light, the material slows down the effective propagation speed of the light waves through the medium. Then the light can be 'speeded up' again to make up for the longer path length around the hidden object.

In this cloak, the object to be concealed is placed inside a hollow metal cylinder coated with acrylic paint, which diffusely reflects light. The tube is embedded within a block of polydimethylsiloxane, a commonly used organic polymer, doped with titanium dioxide nanoparticles that make it scatter light.

"Our cloak takes advantage of the much lower effective propagation speed in light-scattering media," says Robert Schittny, who led the research project. "As we seemingly slow down the light everywhere, speeding it up again in the cloak to make up for the longer path around the core is not a problem."

If the average time it takes light to travel through the polydimethylsiloxane block is in just the right proportion to the average time it takes to travel through the cloak, the core will become invisible.

Schittny and his colleagues hope their cloak will be used in classrooms and labs to excite and educate students about physics.

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