Experiencing something approaching human flight has long been possible. For a price, anyone can leap out of a plane with a parachute, and jetpacks can make up the difference. As for the second, more elusive part of the equation? Researchers from Texas and Toronto say they have invented two different types of invisibility cloaks. For now, these devices only make things seem to disappear on wavelengths undetectable to the human eye, but researchers on both products say a full-scale invisibility cloak is no longer just an impossible dream.
While the allure of the power of invisibility goes back at least as far as H.G. Wells' The Invisible Man—if not Greek mythology— it first became a scientific reality in 2006. That year, researchers at Duke University had created a cloaking device that could make tiny, two-dimensional objects appear invisible to microwaves.
But this cloak, and others like it, were a far cry from anything you'd read about in a Harry Potter book or see in a Star Trek episode (*required references in any article about invisibility cloaks*). One of the major problems, according to a new paper from Dr. Andrea Alú from the University of Texas (Austin), is that while it makes objects invisible in one frequency, it actually makes them more visible under another frequency. An object made invisible in red light, for example, would be even more visible in blue light.
But Alú says he has invented a new type of device that fixes that problem. Like the cloaks of yore, Alú's new design uses meta-materials (synthetic textiles with properties not found in nature) that can bend light around an object and make it look like it's not there. But, by adding an electronic source like a batter to the cloak (making the cloak "active" as opposed to "passive"), Alú says he can make objects transparent at "all angles and over all broad bandwidths."
Naturally, a lot of the funding for this research comes from the Defense Department: Want an airplane or a tank to be invisible to radar? This is the type of device for you. But it's not just the military that is interested. Alú says a good chunk of funding comes from wireless providers. Because if a building is in the way of your wireless signal, making it invisible might be a better alternative than knocking it down.
Alú says he expects to have a version of this device built within the next couple of years.
Why the hurry? Maybe it's so we can get one before Canada does. Researchers at the University of Toronto seem to be neck and neck with the U.S.
In a recent paper published in the Physical Review X, Toronto professor George Eleftheriades and his student Michael Selvanayagam describe a device made up of a series of antennae that can radiate light and radio waves away from the object it surrounds. But these researchers have done more than just write about such a device; they'vejury-rigged one up using Styrofoam, masking tape, and 12 antennae. It cost under $2,000 and has been nicknamed "the active cloak machine."
It essentially works like this: Say you shine a beam of radio waves at an object. When the waves hit the object, they will bounce back. But if you surround the object with antennae that bounce back the opposite radio waves, it will seem as if the object is not there.
When asked who might be interested in such a device, Eleftheriades stuttered a bit.
"The military is the most obvious," he said. "We have been approached…. I shouldn't say too much about that."
As for whether this could ever be applied to making someone or something invisible to the human eye, Eleftheriades says there's no reason it couldn't scale up, it would just need the right kind of antenna (ones that don't yet exist).
So, what do researchers have to say about the age-old question of which would be cooler, flight or invisibility?
"I think becoming invisible," said Eleftheriades. "Because this experience, no human has had it before. Maybe we cannot fly on our own, but we know how it feels to fly."
And despite their friendly competition on the subject, Alú can agree with his colleague on this.
"I would choose invisibility," Alú said. "Flying is easier to achieve in other ways, and I know exactly how hard it is to achieve invisibility.