Real-Life Invisibility Cloak? Physics Points Out The Limits of an Invisibility Device

Harry Potter fans may be devastated to find out that the laws of physics point to the sheer impossibility of a human invisibility cloak.

Researchers at the University of Texas Cockrell School of Engineering in Austin have discovered the fundamental physical limitations of cloaking devices, a technology that makes objects invisible or undetectable to electromagnetic waves such as radio waves, microwaves, visible light and infrared.

While the researchers confirm that it is possible to use an invisibility cloak to hide an object for a specific electromagnetic wavelength, it is highly unlikely that the cloak will hide large objects - such as human bodies - across multiple wavelengths at once.

"The question is, 'Can we make a passive cloak that makes human-scale objects invisible?'" Andrea Alù, electrical and computer engineering professor and a lead researcher in the area of cloaking technology, said in a news release.

"It turns out that there are stringent constraints in coating an object with a passive material and making it look as if the object were not there, for an arbitrary incoming wave and observation point," Alù added.

According to the research, which was published in the journal Optica, cloaks are made of metamaterials, which have special properties that allow for better control of the incoming wave and can make an object invisible or transparent. The limitations established in the research apply to cloaks made of passive metamaterials - those that do not draw energy from an external power source.

The researchers found that the performance of a passive cloak is largely determined by the size of an object to be hidden compared with the wavelength or incoming wave, quantifying how cloaking becomes more difficult for shorter wavelengths.

"We have shown that it will not be possible to drastically suppress the light scattering of a tank or an airplane for visible frequencies with currently available techniques based on passive materials," Francesco Monticone, co-author of the study, said in a statement.

"But for objects comparable in size to the wavelength that excites them (a typical radio-wave antenna, for example, or the tip of some optical microscopy tools), the derived bounds show that you can do something useful, the restrictions become looser, and we can quantify them," Monticone added.

According to the researchers, now that they have figured out the limits of cloaking devices, they would proceed with working to exceed the limits and make improvements on the devices as quickly as possible.

Just recently, another team of scientists from Columbia University has also designed a cloaking device that will be used to hide the Earth from a possible alien invasion.