Tech UPTechnologyThey use sound to levitate multiple objects

They use sound to levitate multiple objects

It is not the first time that Asier Marzo, one of the researchers and teachers of the Department of Statistics, Informatics and Mathematics of the Public University of Navarra (UPNA), explores the extraordinary possibilities of acoustic levitation. In an article published in 2015 in the journal Nature Communications , this expert in computer languages and systems and his collaborators, belonging to different institutions in the United Kingdom, announced the development of a kind of tractor beam that used sound waves to lift and move objects . Over the next two years they refined the process, and at the beginning of 2018 they recorded a remarkable advance in Physical Review Letters : it was not only possible to lift them in this way, but to trap them and keep them stable.

Now, together with Professor Bruce Drinkwater, a mechanical engineer specialized in ultrasound from the University of Bristol, who has also participated in this initiative, he has announced that, for the first time, they have managed to independently levitate multiple particles in this way.

March and Drinkwater point out in an essay collected in the Proceedings of the National Academy of Sciences that, for this, they have used a kind of acoustic tweezers that allow them to manipulate matter without coming into contact with it. “Sound exerts a small force; By increasing the volume of the ultrasonic waves – inaudible to the human ear – scientists have generated an acoustic field strong enough to move different small objects ” , indicates a statement from the aforementioned UPNA and the University of Bristol. In addition, the researchers have devised a new algorithm with which it is possible to generate complex fields, capable of fixing these particles in a certain position.

A future medical revolution

In essence, these acoustic tweezers have capabilities similar to the optics developed by engineer Arthur Ashkin, which use laser beams to trap and move bacteria, and which earned him the Nobel Prize in Physics in 2018. However, the technology for which March and Drinkwater bet is much more efficient and safe from a medical point of view, since ultrasounds can penetrate non-invasively into tissues. And is that one of its possible applications is in surgery: it could be used to manipulate particles inside the body without making incisions. “The flexibility of ultrasonic waves allows us to operate at micrometric scales and move cells within 3D-printed structures or living tissue ,” March highlights in the aforementioned note. “But we can also work on a larger scale and, for example, levitate tangible pixels – made up of particles that levitate – so that they form objects that float in the air. These could be observed from different angles; we would even be able to manipulate them with our own hands ”, he assures.

In one experiment, scientists attached two tiny spheres to the ends of a thread and used their acoustic tweezers to attach it to a piece of cloth. Its system manages to control the movements of up to 25 of these particles in the air at the same time. Very soon they hope to be able to achieve identical results in water and to begin tests on biological tissues.

Reference: Holographic acoustic tweezers . Asier Marzo and Bruce W. Drinkwater. Proceedings of the National Academy of Sciences . DOI:

Images: Groups of millimeter particles levitate over a hand. (Iñaki Zaldúa, Asier Marzo and Bruce Drinkwater) – The researcher Asier Marzo checks the acoustic traps used in the levitation process (Iñaki Zaldúa, Asier Marzo and Bruce Drinkwater).

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