Researchers with the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab) have developed a technique for generating acoustic bottles in open air that can bend the paths of sound waves along prescribed convex trajectories.
The acoustic “bottle” 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. The sound waves are generated by an array of loud speakers, 1.5 centimeters in diameter and spaces 2.5 centimeters apart, operating at a frequency of 10 kilo Hertz (kHz) and can be launched along a designated trajectory by precisely adjusting the phase profile of the speaker array.
Because the high pressure wall of the acoustic bottle exerts a pulling force, there are no sound waves passing through the null pressure interior of the bottle and the bottle can be used for acoustic trapping.
"Our acoustic bottle beams open new avenues to applications in which there is a need to access hard-to-reach objects hidden behind obstacles, such as acoustic imaging and therapeutic ultrasound through inhomogeneous media,” said team member Tongcang Li. “We can also use an acoustic bottle as a cloaking device, re-routing sound waves around an object and then recovering them in their original form, making the object invisible to sonar detection.”
Acoustic bottle beams might also serve another application: acoustic levitation, in which sound waves are used to lift and manipulate millimeter-sized objects, including particles, microorganisms and droplets of water.
Also: Learn about a High-Temperature Surface-Acoustic-Wave Transducer.