It may sound like science fiction but acoustic traps already use sound waves to capture and move objects remotely. Up to now, however, these traps have only worked for very tiny items – up to 2mm. Now Scientists at Bristol University have used a new type of acoustic trap to suspend a larger object steady in mid-air. Their method could allow the exact and careful positioning and manipulation of both millimetre and centimetre sized objects.
In their experiments, Dr. Asier Marzo and colleagues at the University of Bristol used a device that combines two vortex-shaped sound waves to trap objects up to 4 times larger than is possible with existing traps. Their method held a polystyrene sphere within two vortex-shaped acoustic beams. The bead was hit with one beam and then the other, in opposite directions. This process reverses the orbital motion of a particle as it spirals out of a vortex, “pushing” it back into the trap’s centre and capturing particles too big to be contained by a single vortex. The team adjusted the frequency of the pulse to trap particles with diameters up to twice the sound wave’s wavelength. The same system allows them to control and turn a bead in a circle with fixed rotational speeds.
The new method has in effect broken the previous size barrier and could lead to far larger objects being positioned by sound alone. Following further development, the potential uses for acoustic power could have radical repercussions on all our lives.
Acoustic levitation can act on a wide range of substances, from liquids to living animals. In the future, it may be possible to deliver drug capsules or micro surgical implements within the human body. It could even allow transportation without containers and the movement of materials, easily contaminated by touch.
Another exciting prospect is that of contactless production lines, where delicate objects might be put together without anyone or anything touching them. Levitating blood samples could even improve diagnosis.