Creating a cloak that can render a person invisible has been the ongoing dream of materials scientists and Harry Potter fans alike. In the beloved J. K. Rowling
storybooks, the young wizard Harry inherited a magical cloak that could make anyone who put it on instantly invisible.
Now, scientists in the United Kingdom have moved a step forward in the real-world quest for invisibility. Their research, published in the journal Scientific Reports
last week, demonstrates how a so-called "surface wave cloak" can make curved surfaces appear flat when they come in contact with electromagnetic waves.
In other words, the study suggests a way to make such surfaces invisible. How's that for magic?
"The underlying theory can be applied to other wave phenomenon including acoustic and heat waves," said Yang Hao, professor of antennas and electromagnetics at Queen Mary University of London, who led the study.
A new 'cloak' that targets waves
For the study, Hao and his colleagues coated a curved metal plate surface, about the size of a tennis ball, with their cloak. The cloak was made out of a gradient-index material with seven superthin layers that each had different electric properties.
The researchers found that these layers can hide whatever object they cloak from interacting with electromagnetic waves. Otherwise, the electromagnetic waves would bump into the object and scatter in different directions.
The cloak could reduce the scattering of waves used for radio and aerospace communications, said Luigi La Spada, a postdoctoral research assistant at the Queen Mary University of London and first author of the study.
"We believe that our cloaking structure can improve existing technologies and enables future technological innovation," he said. "At the moment, the main interest in surface waves is to develop solutions for reducing and mitigating important telecommunications issues."
In theory, the surface wave cloak also could be used on human bodies, Hao said.
"In this case, wireless sensors are placed on the body," he said. "There have been many attempts to make a real-life cloak but there still exist theoretical barriers."
Why 'magic' was needed in Harry Potter's cloak
Scientists have long explored how manipulating light waves might be at the root of building an invisibility cloak. In 2006, theoretical physicist John Pendry
was one of the first scientists to propose using lenses to bend light
to make an object appear invisible.
Then, in 2013, researchers at the University of Texas at Austin developed a method to make objects appear invisible
within a limited range of light waves using an ultrathin cloak
In 2014, researchers at the University of Rochester developed a cloaking device
with four lenses that can make any three-dimensional object viewed through it appear invisible
Additionally, just last year, scientists at the Department of Energy's Lawrence Berkeley National Lab and the University of California, Berkeley, devised a microscopic cloak
that can conform to the shape of an object and conceal it from visible light.
Most studies on invisibility cloaks use metamaterials and optics to achieve cloaking. But some experts, including optical physicist Joseph Choi, suggest that may be the wrong approach. Thinking digitally, they argue, could lead to a real-life invisibility cloak more quickly.
Choi, who was a member of the research team at the University of Rochester that created the invisibility lens, said they now have created a digital cloak.
The cloak basically measures space as pixels and, by doing so, it collects and emits light in a way to make whatever it is cloaking appear invisible to the human eye.
"We think our digital cloaks can become widespread in 10 years or so," Choi said. "It will likely be an 'active' cloak that requires power to run it, rather than 'passive' cloaks that do not require power. This would allow someone inside the cloak to see the outside while not being seen from the outside.
"I suppose this might be why 'magic' was needed in Harry Potter's cloak, too?"