Who said that invisibility cloaks are just for wizards?
Just as an invisibility cloak in the world of Harry Potter prevents others from seeing a cloaked individual by blocking light waves, a new acoustic invisibility cloak created at Duke shields objects from sound waves. Applications of such a cloak range from building soundproof walls to protecting ships from sonar.“When you try and make something invisible, what you’re trying to do is control how either light or sound reflects off an object,” said Steven Cummer, Jeffery N. Vinik associate professor of electrical and computer engineering, the leading engineer who built the cloak. “If you’re trying to make something invisible in empty space, you have to make sure that it looks like you can see through it and that there’s nothing there so there can’t be any reflections of the object, and the object can’t cast a shadow.”
The design is incredibly simple and can be created using perforated plastic plates, according to the study published in Physical Review Letters. Therefore, companies who are interested in the cloak could easily, and affordably, replicate it.
The cloak, however, is not quite ready to be used outside of the laboratory. Rather than cloaking objects in empty space, the current cloak can only make objects invisible while they are resting on the sound equivalence of a mirror—a flat metal sheet that reflects all of the sounds that hit it. This mirror method is much easier to build, and it requires much simpler materials, Cummer said.
Similar work has been done with invisibility cloaks that block light waves, though those projects are currently only compatible with nanoscale materials and microscopes.
“Everyone has in mind a really great experiment where you can hide a foot-long hot dog sitting on a mirror, but nobody’s there yet,” Cummer said.
Future work on this project will deal with testing the capabilities of these kinds of material in water, he added said.
Although a romantic idea, J.K. Rowling’s invisibility cloaks were not this research tem’s inspiration for creating an inaudibility cloak of their own. Instead, Cummer’s research team built this project off of theoretical work from about five years ago that used mathematics to determine the possible appropriate materials, Cummer noted.
“Harry Potter was not a driving motivation here, but it certainly helps us describe the research we’re doing, the fact that everyone has some sense—either from Star Trek or Harry Potter—of how to make things invisible,” he said.
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