This is not a wind up: scientists can float objects in air using sound
Acoustic experiments that mimic tornadoes could ‘open the door to many new applications’
LEVITATION and Star Trek-style tractor beams are a step closer to reality after scientists proved they can suspend a large object in mid-air, using only sound.
Researchers have been trying for decades to trap objects using sound but it has always proved impossible to hold an item steady if it was larger than the wavelength of the sound.
Objects inevitably ended up spinning uncontrollably and eventually shooting away from the beams, after picking up the movement of the rotating sound field.
But now engineers from Bristol University say they have solved the problem. Instead of using a spinning field of sound to hold an object in place, they have built a device that turns soundwaves into mini tornadoes.
The key difference is that, just like tornadoes, there is a silent core in which the object can hover. By rapidly changing the rotational direction of the mini-twisters, researchers found the core increased in size, allowing larger objects to be levitated.
Dr Asier Marzo, from the university’s department of mechanical engineering, said: “Acoustic researchers had been frustrated by the size limit for years, so it’s satisfying to find a way to overcome it. I think it opens the door to many new applications.”
Magnetic levitation uses magnetic fields to suspend objects in mid-air. While acoustic levitation is not as strong as magnetic levitation, it can act on a wide range of materials, from liquids to living animals.
Working with ultrasonic waves at a pitch of 40khz – a similar pitch to that which only bats can hear – the researchers held a 2cm polystyrene sphere in the tractor beam.
This sphere measures over two acoustic wavelengths in size and is the largest yet trapped in a tractor beam.
The researchers say the new device opens the door to the manipulation of drug capsules or micro-surgical implements inside the body. It could even allow containerless transportation or help scientists and engineers move around delicate materials which could be contaminated by touch.
Dr Mihai Caleap, senior research associate, explained: “In future, with more acoustic power it will be possible to hold even larger objects.
“This was only thought to be possible using lower pitches making the experiment audible and dangerous for humans.” The research, published in the journal Physical Review Letters. suggests that in the future, much larger objects could be levitated in this way, possibly even humans, or vehicles.
Bruce Drinkwater, professor of ultrasonics at the university, who supervised the work, added: “Acoustic tractor beams have huge potential in many applications. I’m particularly excited by the idea of contactless production lines where delicate objects are assembled without touching them.”
It even has the potential to improve diagnosis through blood tests.
Dr Marzo added: “Levitating samples in mid-air can improve diagnosis from blood samples and detection of the structure of molecules.”
Levitation has long been a staple of the conjuror’s art, but so far they have failed to convince the scientific world that they really can float into the air. If British researchers are to be believed, however, the age of true levitation may be upon us, as a new technique allows objects – and even liquids – to be manoeuvred off the ground. Sound too good to be true? On the contrary, for sound waves are themselves the impulse that gives the idea lift. It’s an attractive thought too, for the waves can also act like a tractor beam. What’s next? Will physicists prove that it really is possible to store an infinite number of handkerchiefs in a top pocket, or biologists that the natural habitat of rabbits is genuinely the top hat? Arthur C Clarke is finally being proved right: “Any sufficiently advanced technology is indistinguishable from magic.”