A tractor beam (the word tractor meaning ‘traction’ rather than a farm vehicle!) is a tool that’s often used in science-fiction; it’s a controlled beam of energy that is able to grasp and manipulate solid objects. Now scientists around the world are beginning to make headway in this area, and the tractor beam could soon be a reality.
A team of scientists at the Public University of Navarre in Spain have developed a sonic tractor beam. Using ultrasound waves they’re able to move objects such as polystyrene beads up to the size of a pea. They do this by having an array of 64 flat speakers that can emit ultrasonic waves in various directions and patterns, creating a 3D ‘acoustic hologram’. How? Sound waves, like all waves, have peaks and troughs; where the peaks of the ultrasound waves meet they become larger, and when a peak of one meets a trough of another they cancel each other out. In this way a shape such as a hand, tweezers or a cage can be created by sound waves alone, thus enabling the capture and manipulation of the target.
The team, led by Asier Marzo even made a cardboard spaceship to demonstrate that they could ‘suck up’ an object in traditional science-fiction style – you can see it on their video of the sonic tractor beam in action. Although work has been done in this area before, this technology is more advanced and more practical because it only requires a single flat array of speakers, instead of several arrays surrounding the target.
The team aren’t planning to capture any spaceships with their technique though (not least because sound waves can’t travel in a vacuum!). Instead they’re focusing on making the technology smaller and easier to manipulate. This is partly because the larger the object to be moved, the lower the frequency needs to be. If you wanted to levitate a football, for example, the sound waves would need to be so low that they were hazardous to human health.So the team envisages this technique being used in medicine, enabling surgeons to manipulate or remove obstacles such as kidney stones or blood clots without ever having to make an incision in the patient. Another potential application is the creation of 3D touchscreen displays, which Marzo says could be on the market within the next 5 years.