Scientists in the United States reported a further step towards a celebrated “invisibility cloak” by masking a large, free-standing object in three dimensions.
The lab work is the latest advance in a scientific frontier that uses novel materials to manipulate light, a trick that is of huge interest to the military in particular.
Reporting in the New Journal of Physics, researchers at the University of Texas in Austin cloaked an 18-centimetre cylindrical tube from light in the microwave part of the energy spectrum.
Those hoping for a Harry Potter-style touch of wizardry would be disappointed. To the human eye, which can only perceive light in higher frequencies, no invisibility would have been seen.
But, say the researchers, the experiment is important proof of a principle that so-called plasmonic meta-materials can achieve a cloaking effect.
A warplane cloaked with such materials could achieve “super-stealth” status by becoming invisible in all directions to radar microwaves, said co-lead investigator Andrea Alu.
Plasmonic meta-materials are composites of metal and non-conductive synthetics made of nanometre-sized structures that are far smaller than the wavelength of the light that strikes them.
As a result, when incoming photons hit the material, they excite currents that make the light waves scatter.
The new experiment entailed making a shell of plasmonic meta-materials and placing the cylinder inside, and exposing the combination to microwaves.
Microwaves scattered by the shell ran into microwaves bounced from the object, preventing them sending a return signal to the viewer.