Remember Star Trek? Among the many jaw-dropping features it had, tractor beams were one of those that fascinated me most: a system that could deploy a force on an object over distance, pushing or pulling it.
That was science fiction. As with several other magics we saw in Star Trek also tractor beams are leaving the field of fiction entering in the one of Science. At the Washington University a team of researchers is working on ultra-sounds to create tractor beams.
They started in the small, using optical tweezers (electromagnetic fields) to manipulate nanoparticles forcing them to assemble in the desired order and structure. They moved on to use ultra-sounds for lithotripsy (fracturing in small pieces kidney stones so that they can be expelled).
Now they have created a system that is able to create ultra-sound beams that can move (small size) objects, as shown in the clip. They are able to direct and regulate the ultra-sound power to generate a force acting on the object. Sensors measure the effect and the system finely tune the beams direction and intensity to achieve the desired effect. As shown in the clip an object can levitate, kept floating in the air by invisible ultra-sounds.
It is not -yet- the kind of tractor beam foreseen in Star Trek but it is real applied science. According to the researchers this technology might also be used to generate holograms.