From science fiction to reality. A team of researchers from the University of Bristol (United Kingdom) together with the Spanish computer engineer Asier Marzo, have used the most powerful acoustic tractor beam in the world, demonstrating that it is possible to stably contain objects with a wavelength greater than that of sound. . This sonic beam tractor opens the door to the possible levitation of other much heavier objects and even human beings.
The key to overcoming previous obstacles that caused objects to become unstable, spinning so fast and uncontrollably that they were thrown out of the range of the acoustic tractor beam , has been the use of rapidly fluctuating acoustic vortices. In this way, it has been possible to control the rotation speed of the objects with great precision by rapidly changing the twisting direction of the vortices, an effect that stabilizes the tractor beam.
In other words, scientists have been able to levitate notably larger objects than was ever possible before.
Acoustic tractor beams use sound, or more specifically sound waves, to keep particles in the air. Unlike magnetic levitation, acoustic levitation tends to work better for handling liquids and solids.
The study describes the new technique, which creates a tornado-like structure that is extremely noisy but has a quiet core.
The researchers found that when they changed the direction of the rapidly fluctuating acoustic vortices that make up this structure, they could control the speed of rotation and stabilize the tractor beam. By stabilizing it, they were able to contain larger objects.
“Acoustic researchers have been frustrated by the size limit for years, so it is satisfactory to find a way to overcome it,” explains Asier Marzo, leader of the work to the journal Physical Review Letters that collects the study.
In the detailed demonstration in the study, the researchers used ultrasonic waves at a pitch of 40 kHz to form the acoustic vortices. The silent core of the structure could contain a two-centimeter sphere made of a synthetic polymer , making it the largest object that has been stably held on a tractor beam so far.
Practical applications
Medical devices, such as drug capsules or microsurgical instruments, would be one of the interesting applications of this advance.
Researcher Bruce Drinkwater, who is overseeing the work, added that acoustic tractor beams have incredible potential in many applications, enabling non-contact production lines where delicate objects are assembled without the need to touch them.
And in the future, with more acoustics, it would be possible to hold even larger objects like a person.
Reference: Asier Marzo, Mihai Caleap, and Bruce W. Drinkwater: Acoustic virtual vortices with tunable orbital angular momentum for trapping of Mie particles. Physical Review Letters 2018 DOI: https: //doi.org/10.1103/PhysRevLett.120.044301
The most powerful acoustic tractor beam ever
