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A Tractor Beam Made of Sound Waves Can Move Around Centimeter-Sized Objects

Tractor beam

Tractor beam. This schematic shows how sound waves normally pushed an object away, in (a) and (b). But if they are aimed at an object as in (c), that is also appropriately shaped, the object can be pulled toward the acoustic source. Image credit: APS/Alan Stonebraker.

Tractor beams, also called as “attractor beams,” which can get an object closer to another distant one, do often appear in science fiction. Is it possible that we can really use them in our daily life?

Earlier this year, scientists claimed that they had produced a type of tractor beam, also known as “optical tweezers”. Such beam was able to move around nano-sized objects with light.

NASA researchers are also engaged in a project to reel in objects with light. At the same time, Australian scientists have succeeded in moving small objects with lasers for a distance of five feet.

Actually, all these work are closely linked with application of light. However, a separate group of scientists has created an acoustic tractor beam, which is capable of moving much larger objects by the means of sound waves.

This device incorporating more than a thousand ultrasound emitters, were placed underwater. When switched on, it could tug along centimeter-sized objects, such as a small hollow triangular shape. Generally speaking, sending acoustic beams at something would cause it push away. However, the scientists found that if they could control the angle of sound waves precisely, they would be able to establish a low pressure zone ahead of the object so as to pull it closer.

Up to now, this kind of technology has its limitations, because it is unable to be applied in space owing to the fact that sound cannot travel in a vacuum. However, it may find its applications in some biomedical areas, for example it could be used to manipulate objects beneath skin or within organs, but involving any cutting.

According to Gabriel Spalding, a physicist from Illinois Wesleyan University and co-author of the study published in the journal Physical Review Letters, the application of such technology for medical diagnosis is similar to the tomato-freshness test in the way that by squeezing cells, doctors could identify whether they are normal or cancerous or metastatic.

Journal reference: Démoré, Christine EM, et al. “Acoustic Tractor Beam.” Physical Review Letters112.17 (2014): 174302.

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