New 'Active' Invisibility Cloak Shields Across Light Frequencies

Back in 2006, scientists developed the first invisibility cloak, but it wasn't yet able to make an object appear invisible to human vision. Now, a new type of invisibility cloak takes us one step closer to that goal.
So far, scientists have developed more than 10 cloaking devices, and the latest invisibility cloak is thinner model using "active" technology or electric power. Invented by University of Texas at Austin scientists, the new cloak enables more effective shielding of an object at a wider variety of light frequencies.
For example, an object invisible in red light would also be invisible in blue light; with previous cloaks, an object would disappear in red light, but appear in blue light, as explained in the team's recent research paper on The Physical Review X.
During experimentation, scientists made a cylindrical rod invisible, and determined this with the aid of machines and systems tracking microwave or radio frequencies, which are outside of what humans can see in the visible light spectrum. Light frequencies are all in the electromagnetic spectrum, where visible light wavelengths are a very small part of the spectrum that is visible to the human eye.
Made from a thin layer of metamaterials or synthetic textiles with properties not found in nature, the cloak bends and scatters light around the rod. The cloak then makes the rod disappear at the microwave or radio frequency level.
Led by University of Austin professor Andrea Alù, the research uses electronic amplifiers in the ultra-thin cloak — known as "active" technology — which relies on electrical currents to make an object disappear over a broader light-frequency range. Previous invisibility cloaks were not as physically thin and failed to fully shield an object since the "passive" technology required no power source and used limited bandwidths.
The passive cloaks "scattered more waves than the bare object they were trying to hide - when tested over the whole range of the electromagnetic spectrum," as reported by the BBC. Therefore, passive cloaks only made an object invisible in a specific light frequency range and not across different ranges.
Research team member Jason Soric says electronically powered cloaks change the functionality of previous "passive" cloaking devices. "The active cloaking works over a much larger bandwidth than any other passive cloak, especially considering, that it cloaks at all angles, and not just in one direction.
"Embedding electronics into passive cloaking covers has been shown to allow great control over the surface current needed to cancel the scattering of bare objects," Soric told Mashable in an email.
Currently, the University of Texas scientists are working on a cloak prototype that should be available in the next few years.