Levitation Becomes a Reality

October 23rd, 2015
A real-life sonic tractor beam has been developed in the United Kingdom, with this exciting breakthrough set to influence the worlds of technology and medicine over the next few decades. While acoustic levitation has been achieved before, previous efforts always involved surrounding the object with speakers. The use of a single-sided device to manipulate objects greatly extends the potential of this technology, allowing the manipulation of "cells, liquids, compounds or living things without touching or contaminating them."

Published last month in Nature Communications, "Holographic acoustic elements for manipulation of levitated objects" is a ground breaking study that builds on previous work by the University of Dundee. While the objects moved were only 1mm in size, this proof of concept already has a number of exciting implications. The medical potential of this technology will be explored immediately, with large-scale Star Trek-style physical manipulation not out of the question in decades to come.

According to co-author Bruce Drinkwater, Professor of Ultrasonics at the University of Bristol, "We've all experienced the force of sound - if you go to a rock concert, not only do you hear it, but you can sometimes feel your innards being moved... It's a question of harnessing that force." The potential uses of this technology include tractor beams, manipulation of drugs and other objects inside the body, and non-contact production lines for handling delicate objects. Manipulating large objects with acoustic energy may even become possible, with some fringe researchers suggesting that this is how the ancients moved heavy monoliths.

While previous work in this field also moved objects with sound, circular speaker systems dramatically decrease the real world potential of acoustic levitation. According to Drinkwater, "Single-sided devices potentially enable in vivo manipulation since the device could be applied directly on to the skin with the manipulation taking place inside the body; similar to an ultrasound scanner but for manipulating particles (that is, drug capsules, kidney stones or micro-surgical instruments)... This is a significant advantage over two-sided opposed arrangements, which require the target area to be sandwiched by the arrays; also, single-beam traps do not have repeated patterns that could accidentally trap other particles."

The success of this demonstration builds from previous work at the University of Dundee, with researchers there not able to perform working levitation but still discovering the existence of a force attracting acoustic waves back to their sound source. By turning this force into a stable working device, Professor Drinkwater and his team used "Acoustic structures shaped as tweezers, twisters or bottles... as the optimum mechanisms for tractor beams or containerless transportation."

According to Professor Drinkwater, the team's success lay in the absence of a mathematician amongst them: "Not being mathematicians, we did not seek elegant solutions but used what I call 'brute-force inversion' to solve the problem." Instead of math, computer simulations were run through a wide range of different sound wave patterns, with the ones that produced the signature combination of a low-pressure region surrounded by high-pressure zones found to have the most success in manipulating physical objects.

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