Researchers have developed a technique for generating acoustic bottles in open air that have the ability to bend the paths of sound waves along convex trajectories.
Sound waves travel on a straight path, but can be bent through diffraction or refraction. Researchers have been looking for a way to develop techniques to bend the path of sounds waves along a curved trajectory to meet the needs of high resolution imaging, Berkeley Lab reported. Artificial nanostructures called "metamaterials" have been built to bend sound waves, but these devices come with significant limits.
"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. "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."
The bottle features a three-dimensional curved shell in which a wall of high acoustic pressure surrounding a null pressure region. Sound waves forming in the bottle are concentrated into a beam that travels down the walls. The waves are created using loud speakers.
"Since the principle of adjusted phased arrays is well-established and now being used in ultrasound imaging, we can directly apply our acoustic bottle beam technique to current acoustic systems," said Peng Zhang, lead author of the paper, published in in Nature Communications. "Our technique offers a new degree of freedom for controlling the flow of acoustic energy at will."
The bottle allows for "acoustic trapping" that is not influenced by obstacles placed within the bottle. The findings could be used in acoustic imaging and therapeutic ultrasound through inhomogeneous media. It could also be used as a cloaking device because of its ability to re-route sound waves. Acoustic levitation is another possibility.
"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, another co-author of the paper. "For example, by creating this three-dimensional bottle-like acoustic trap, we could use it as a micro-chemical reactor and manipulation of biological trafficking devices."
