In a novel, but not entirely unique, approach to levitation, scientists can now control levitating objects in a 3D plane. They use four ultrasound emitting panels, in a square shape, which emit at the same time. They can focus the emissions onto a single focal point, which they can move around within the area between the panels, by changing how much each panel is emitting. Two of the speakers are used for levitation, and the other two control where the focal point is. Particles become trapped in the nodes (the parts of a wave which remain stationary) of the standing waves, and multiple objects can be levitated at once.
Progress in the field of levitation could one day allow us to finally have hoverboards that science fiction promised us years ago. At the moment, the large amount of mass that needs to be lifted by the small base of the board is making it impractical to make hoverboards, but this could all change one day. More ordinary include a method of repelling rain from windshields, which is already being worked on. Looking at the video of the project, it does appear in some cases that the object being levitated is not entirely stationary – it looks like it rotates slightly in the air, which could be a result of the multiple waves approaching it from different directions. This could become more stable as more work is done on the area, making the whole process more feasible for actual practical use. Also, the amount of energy that would need to be put into the speakers to generate ultrasound waves with the capacity to lift larger objects could be rather large, so again, more research still needs to be done until we can see more than simply matchsticks being lifted. Though the fact that they managed to lift something as solid as a nut, after starting with very light polystyrene balls, is an impressive starting point.
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For more take a look at: http://www.wired.com/design/2014/01/whoa-watch-scientists-control-levitating-beads-with-sound-waves/