Human levitation and Star Trek-style tractor beams have moved a step closer after scientists proved they can stably hold a large object suspended in mid-air, using only sound.

Researchers have been trying for decades to trap objects using only the power of 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 the University of Bristol 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 which turns to soundwaves into mini tornadoes.

The key difference, is that, just like tornadoes, there is a silent core in which the object can hover. And 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, lead author on the paper from Bristol's Department of Mechanical Engineering, said: “Acoustic researchers had been frustrated by the size limit for years, so its satisfying to find a way to overcome it.