“Scientists close to perfecting a Harry Potter-style invisibility cloak” -- does this headline seem familiar?
It seems like every six months, some group of scientists is rushing to claim the boy wizard’s mantle. But most of these devices are still very far from being able to confer what the average person would think of as invisibility -- being shielded from visible light.
One of the first "cloaking devices" came to light in 2006, when Duke University scientists were able to build a material that steers microwaves around an object.
Then in 2008, a team led by University of California at Berkeley scientists described ways to make such “metamaterials” that could warp various other wavelengths of radiation, including light. Chinese scientists soon followed up with a theoretical model for an anti-invisibility cloak that would counter a metamaterial’s light-bending ability from the inside. This would partially solve the problem that a truly perfect invisibility cloak would let in no light at all, leaving anyone cloaked in it blind.
In 2009, Duke University scientists used a device that looks like a yellow bathmat to cloak a small bump from microwaves and infrared light. In 2011, University of Texas at Dallas researchers used material made from carbon nanotubes to create a mirage-like effect that hides objects from light -- though it works best underwater.
"If there is adequate funding, I'd have thought [making an invisibility cloak for visible light] would take in the order of five years," Imperial College London researcher John Pendry told the Telegraph seven years ago.
The latest “invisibility cloak” model was developed by physicists from the University of Texas at Austin, who described their device in a paper published Monday in the New Journal of Physics. The UT Austin device, called a “metascreen,” was made by attaching thin strips of copper tape in a fishnet pattern to a sheet of polycarbon film less than a millimeter thick.
The metascreen successfully cloaked an 18-centimeter-long cylindrical rod -- from microwaves, not visible light. It does this by canceling out the microwaves that bounce off of the surface of the object underneath the cloak. The team does think the principle could eventually be replicated with visible light, as well as other wavelengths -- X-rays, or sound, for example.
In a statement, co-author Andrea Alu said that a metascreen shielding against visible frequencies would be easier to manufacture than other kinds of cloaking devices.
It doesn’t seem like a visible-light metascreen would be able to cloak anything that’s ordinarily visible to the naked eye, however.
“The size of the objects that can be efficiently cloaked with this method scales with the wavelength of operation, so when applied to optical frequencies, we may be able to efficiently stop the scattering of micrometer-sized objects,” Alu said. (A micrometer is equivalent to one-thousandth of a millimeter.)
The technique could come in handy in biomedical instruments and other engineering applications that work on the tiniest of scales, but don’t expect to be able to duck under an invisibility cloak made with this material anytime soon.
While it may be tempting to snicker at the yearly parade of invisibility cloak stories as an exercise in overhype, it is nonetheless impressive that scientists have been able to muck about with fundamental forces of nature this successfully. You could also see it as an illustration of the way that science builds upon previous works, bit by bit, knitting the threads together.