Real-life invisibility cloak makes objects vanish

German scientists have developed a real-life 'Harry Potter-style' portable invisibility cloak that can effectively shield small objects.
The cloak developed by researchers from the Karlsruhe Institute of Technology (KIT) in Germany is a solid-state device that can be taken into classrooms and used for demonstrations.
It can not hide a human, but it can make small objects disappear from sight without specialised equipment, researchers said.
Researchers constructed the cloak from a light-scattering material that slows down the effective propagation speed of the light waves through the medium.
Then the light can be sped up again to make up for the longer path length around the hidden object.

In the 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," said 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," said Schittny.

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.
On the other hand, the completely solid-state cloak can be easily transported to classrooms.
"It is a macroscopic cloak that you can look at with your bare eyes and hold in your hands," said Schittny.
"With a reasonably strong flashlight in a not too bright room, it is very easy to demonstrate the cloaking. That means no fancy lab equipment, no microscopes, no post-processing of measurement data. The effect is just there for everyone to see," Schittny added.