Scientists Discover New Method to 'Bottle' Sound Waves
Scientists have discovered a new way to "bottle" sound waves. They've developed a technique for generating acoustic bottles in the open air that can bend the paths of sound waves along prescribed convex trajectories.
Sounds waves move a lot like light waves. They travel on a straight path until they hit an object. In fact, this path, through reflection, diffraction or refraction, can be bent. This is the basis for ultrasound medical imaging and non-destructive testing of materials. In recent years, scientists have been looking for a way to bend the paths of sound waves in order to meet the more stringent demands of super high-resolution imaging and other applications. While "metamaterials" have been engineered to bend sound waves sufficiently, though, the nature of these materials places limits on their applications.
That's why scientists decided to take a closer look at sound waves to create a new technique. They created an acoustic "bottle" that features a three-dimensional curved shell, in which a wall of high acoustic pressure surrounds a null pressure region in the middle. Sound waves forming the bottle are concentrated into a beam that travels through the high pressure wall of its curved shell.
"We need to find ways to bend acoustic wave fields without depending on the use of a highly engineered medium," said Xiang Zhang, director of Berkeley Lab's Materials Sciences Division, in a news release. "With our bottle beam technique, we can design and synthesize acoustic bottles that are capable of directing sound waves along paths of desired curvature through homogeneous space without the need of metamaterials or any other highly engineered medium."
So how can these bottle beams serve researchers? They could open new avenues to applications in which there are a need to access hard-to-reach objects hidden behind obstacles, such as acoustic imaging and therapeutic ultrasound through inhomogeneous media. In addition, it may also be possible to use an acoustic bottle as a cloaking device by re-routing sound waves around an object.
"These giant acoustic traps could lead to new technologies and devices for a variety of applications in chemistry, materials, as well as biosciences," said Sui Yang, author of the paper describing the method.
The findings are published in the journal Nature Communications.