Open-Air Acoustic Bottle Developed
For years now, people have been fascinated by metamaterials, which can make light and sound waves do the unexpected, including creating invisibility cloaks. The fact that these are actual devices though limits their effectiveness, so researchers have been looking for ways to replicate the results without special mediums. Those at Berkeley Lab have recently discovered how to create an acoustic bottle in open air.
An acoustic bottle, like the name suggests, is a bottle of sound with the sound waves travelling around a space, instead of passing through it. As the center is pressure neutral, whatever is in it will not interact with the sound waves, like how an invisibility cloak works. To achieve this without a metamaterial for the sound to pass through, the researchers used an array of speakers and carefully tuned the sound's phase profile across it. Phase is a property of waves that represents the position of the crests and troughs, and by changing it one can control how waves will interfere with each other. In this instance the interaction creates a high pressure wall around a space that will actually pull sound waves into the wall, and around from the space.
Potentially acoustic bottles could be used for routing sound waves around objects, cloaking an object from sonar detection or avoiding obstacles to ultrasound imaging. Also it could be used for achieve acoustic levitation, which can manipulate millimeter-sized objects.
Source: Berkeley Lab