Scientists from the University of Bristol have demonstrated for the first time that sound waves can hold objects larger than the wavelength in the air. The technology is paving the way for the use of sound to manipulate drug capsules and micro-instruments inside the human body, the researchers said.
In the long term, in this way it will be possible to move heavier objects and, who knows, perhaps even people.
Previous attempts to use sound waves to manipulate particles that are larger than the wavelength have failed. The objects behaved unstably: they rotated uncontrollably and "jumped out". Scientists believed that it was not possible to get around this limitation.
Researchers at the University of Bristol set out to create fast-paced, tornado-like acoustic vortices with a calm core. Scientists have demonstrated that the speed of rotation of an object can be varied by changing the direction of the swirling vortices. In addition, the specialists managed to increase the size of the calm "core", thanks to which it was possible to keep larger objects in the air.
So, using ultrasonic waves with a frequency of 40 kHz (the same frequency is used by bats for echolocation), scientists were able to hold a foam ball with a diameter of 2 cm. The diameter of the ball turned out to be approximately 2 times larger than the wavelength.