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Making something invisible does not require complex materials and techniques. Well-placed mirrors or lenses can cloak fish, cats and even people, two new studies show.
Since 2006, physicists have engineered intricate materials that can steer light waves around an object to render it invisible. But such cloaks can manipulate only a narrow range of wavelengths, a far cry from the full spectrum seen by people.
John Howell, a physicist at the University of Rochester in New York, realized that plenty of simple, off-the-shelf materials can also steer light. During Thanksgiving break last year, Howell and his 14-year-old son Benjamin designed three devices that hide life-size objects from sight. One uses L-shaped water tanks, another a network of lenses and the third a set of mirrors; all of them function on the principles of reflection and refraction that students learn in high school physics. The Howells reported June 10 at arXiv.org that they cloaked chairs, toy helicopters and people, though the cloaks worked only when viewed from one direction.
The work, Howell says, “doesn’t discount the beautiful stuff other people have done, but it shows that there are simple ways of doing it too.”
Halfway around the world, a team led by Hongsheng Chen at Zhejiang University in China employed a similar approach to cloak a fish in a tank and a cat. Chen’s team built square and hexagonal glass enclosures that acted as prisms to bend light around an object inside, they report June 7 at arXiv.org. The fish seemed to disappear as it entered a cloak placed in its tank, while the plants the background remained visible.
John Pendry, the Imperial College London physicist who first proposed making invisibility cloaks from synthetic materials, notes that the new cloaks’ simplicity requires some sacrifices: These cloaks will never be able to hide an object from all directions, he says.
Nonetheless, one of the new cloaks may have practical use. Howell suggests that a mirror- or lens-based cloak could conceal a secret satellite from observers on the ground. At the very least, the papers offer a recipe for people to concoct their own simple and fun cloaks.
A goldfish swims through a glass cloak designed by researchers in China and Singapore. The cloak guides light around objects inside of it, making the fish disappear while the plants in the background remain visible.
Credit: Hongsheng Chen et al