A few steps closer to Harry Potter’s invisibility cloak

 

One of the keys to invisibility is bending light. Image: Shutterstock

Now you see it… science can make things invisible.

Researchers are trying to devise invisibility mechanism. Here, you’ll find the most promising ones.

Bending light
The usual approaches call for light to be bent in some way around the object (or person) in question, rendering them invisible. But light needs to be accelerated to high speeds or the invisibility will be restricted to one colour in the spectrum.

Ideal if the subject is motionless and camouflaged, but any movement would reveal the object.

Janos Perczel, from the University of St Andrews in the United Kingdom, found a solution for the speed problem in August 2011. He added an optical device to the invisibility cloak that slows down light and allowing to work in all parts of the spectrum… while remaining invisible itself.

Working blind
Metamaterials, a popular choice for creating cloaks, are effectively invisible because they absorb, bounce, absorb, reflect, scatter and otherwise alter light rays that strike them. Scientists at Duke University, US, demonstrated in 2006 that an object made of metamaterials is partially invisible when viewed using microwaves.

But it’s a two-way street- if light doesn’t penetrate the cloak, the person inside can’t see out. Huanyang Chen and his colleagues from Shanghai Jiao Tong University, China, solved this problem by creating an ‘anti-cloak‘, which guides light back to the object and causes it to become visible again.

“With the anti-cloak, Potter can see outside if he wants to,” says Chen. But he’d be unmasked in the process.

Different materials
On January 26, 2012, scientists from the University of Texas, US, found a way to cloak a three-dimensional, free standing object. Using plasmonic metamaterials, an 18 centimetre cylindrical tube was hidden from microwaves.

Plasmonic metamaterials have the opposite scattering effect to everyday materials, causing them to cancel each other out. The overall effect is transparency and invisibility at all angles of observation, according to co-author Andrea Alu. “The goal was simply to show that one can practically realize a cloak that can suppress the scattering in all directions, and not just in specific directions and for waveguide environments,” he said.

It is possible to translate these concepts from the microwave range to optical wavelengths, but for much smaller objects than we usually envisage. ” We are far from cloaking a human body,” Alu said.

“Our envisioned applications are quite different.

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