Duke engineers demonstrated acoustic cloaking through rigorous research and metamaterials. The designers set out to create a 3 dimensional form that would essentially slow sound waves thereby giving the impression that nothing impeded the sound. The 3D printed cloak covers objects that would reflect sound waves as soon as it hits the object. With the demonstration of an acoustic invisibility cloak, numerous application emerge in its wake.
In order to create the proper cloak, the engineers turned to metamaterials, an emerging field that combines natural materials with repeating patterns to achieve unnatural properties. In Duke’s case, they found success with plastic and air. The repeated holes in the 3D printed sheet material, layered on top of each layer forms a pyramid structure. Essentially, the cloak alters the trajectory of the sound waves to give the impression that they do not hit anything and simply progress as if an object were not in the way. While the end result looks elegantly simple, the effort and brain-racking proved arduous.
“The structure that we built might look really simple,” said Cummer, professor of electrical and computer engineering at Duke University. “But I promise you that it’s a lot more difficult and interesting than it looks. We put a lot of energy into calculating how sound waves would interact with it. We didn’t come up with this overnight.”
The ramifications of the successful acoustic cloak spreads in various directions. One obvious application is in sonar. Since sound waves behave similarly underwater and in the air, it is foreseeable to find this technology used in sonar avoidance. The research received funding from the Office of Naval Research and Army Research Office, so military interest is a forgone conclusion. Yet in another arena, Cummer sees cloaking used to improve auditoriums and concerts no longer hindered by choices deciding between pragmatism and acoustic aesthetics. In fact, if used efficiently, the mantra could finally be true that there is not a bad seat in the house.