Scientists Develop Acoustic Cloaking Device
Engineers from Duke University have made the first three-dimensional acoustic cloak. With some perforated sheets of plastic and some serious number crunching, they made the device which reroutes sound waves to give the impression that the cloak and anything beneath it are not really there.
According to the article in Science Daily news, the acoustic cloaking device works regardless of the direction from which the sound originates or the location of the observer. The engineers said that the discovery has potential for being used in future applications like sonar avoidance or architectural acoustics. The original study appears in the online science journal Nature Materials.
Steven Cummer, professor of electrical and computer engineering at Duke University, explained that they were performing the trick of hiding an object from sound waves. They placed the cloak around an object and caused the sound waves to act like there was only a flat surface in their path.
The team used a developing field of study, metamaterials, which involves the combination of natural materials in repeating patterns to form properties that are unnatural. For the cloak, plastic and air were the materials incorporated. The resulting device had the appearance of numerous plastic plates that had a repeating pattern of holes in them while they were stacked on top of each other to create a pyramid-like structure. The cloak had to alter the trajectory of the waves in a way that matches what their appearance would be if reflected off a flat surface. The sound never reaches the surface below so that it travels a shorter distance and its speed needs to be slowed down to compensate.
The reason for the experiment, Cummer explains, is to show that the technology is possible.