Cloaking devices, a staple of science fiction (think Harry Potter), are getting closer to reality. Researchers at Duke University have built a structure that would hide anything under it from sonar — at least in air.
Made of sheets of perforated plastic, the pyramid-shaped cloak changes the shape and speed of sound waves as they hit it. Those changes make the sound waves appear to reflect off the surface the pyramid is standing on, as though it wasn't there.
To build the cloak, Lucian Zigoneanu, Bogdan-Ioan Popa and Steven Cummer modeled the way sound waves act on a computer. They tried several simulated shapes, and eventually came up with the pyramid design, made with sheets that have holes in them.
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