Ultra-thin skin created by US scientists can be laid over 3D shapes to make them look flat using thousands of nanoscale dots to reflect light





Harry Potter donned his to explore Hogwarts undetected, but an invisibility cloak made by US scientists could find a far more pressing use: making beer bellies look like six-packs.



The ultra-thin skin developed by researchers in California can be laid over a 3D shape to make it look like a flat surface, or even a surface with very different contours to the real ones hidden underneath.

The cloak works its magic by being studded with thousands of nanoscale dots that act like antennas for light. When light falls on the cloak, the dots alter the reflected light waves in such a way that the object appears to be flat.



“It’s the first time we’ve done arbitrary shape cloaking, said Xiang Zhang, who built the device at the University of California, Berkeley. “If you want to cloak people, that is possible with this new work.”



Up to a point. The cloak will not make someone seem to vanish into thin air. Instead, it can make an object appear flat, or another shape, when viewed from the front, and over a limited range of optical wavelengths. In principle it could be scaled up and worn, but move around and the illusion would fall apart.



Previous invisibility cloaks have been hopelessly impractical - for hiding people at least - on the grounds of size alone. “They are really bulky,” said Zhang. “If you wanted to cloak your body, you’d have to carry this thing that’s three to four times the size of your body around with you wherever you go.”



Sir John Pendry, a pioneer in the field of invisibility cloaks at Imperial College, London, adds that older versions of invisibility cloaks are more like a shed than a young wizard’s cloak.



Zhang’s cloak is microscopic in size and has succeeded so far in hiding only tiny objects. But he believes the skin can be scaled up to form sheets that can cloak much larger objects.



Facebook Twitter Pinterest The reflecting image of the cloak wrapped over a bump is recorded through a widefield microscope. The bright stripe in the middle at the beginning is the bump. It becomes invisible when the cloak is switched on.

His breakthrough came when he worked out how to cover thin sheets of material with the nanosized gold dots. The dots are made in different sizes that determines how they absorb and re-radiate light that falls on them.



When light falls on a 3D object, the waves that reflect back are distorted, and it is these changes to the light that reveals the object’s shape. By tuning the gold dots to absorb and re-radiate light in different ways, Zhang’s cloak can either undo the distortions, so the reflected light looks as if it has come from a flat surface, or create new ones, making the surface look rippled or full of bumps.



“One application might be in cosmetics,” Zhang said. “You can imagine if someone has a fat belly, like me, and he wants to look nice, he could put this layer on and it will look like a six pack.” He found at least one potential customer in Professor Pendry. “Right on!” he said. “I need that.”

Zhang believes that future versions of the cloak - made on thin, flexible sheets - could also help to cover up serious facial injuries. Details of the cloak are reported in the journal Science.



“They address the problem of a cloak’s thickness and come up with a smart solution that enables them to make a very thin cloak,” said Pendry. “I would rather think of this cloak as a device for altering the apparent shape of an object, making it appear to be something that it is not. That could be very useful in stealth technology.”