Ultrasound can levitate large objects
Scientists show that acoustic levitation now works for targets larger than the wavelength.
Scientists have long dreamed of using acoustic levitation to float objects, but there has been one big catch: you couldn't lift an object larger than the wavelength without being picky about what you're lifting. However, it might not be a problem going forward. Researchers in Brazil and the UK have successfully levitated a polystyrene ball 3.6 times larger than the ultrasonic waves holding it up. The trick was to create a standing wave in the gap between the transducers and the object, instead of the usual pressure node between the transducer and a reflector. You can change the angle and number of transducers without messing with the effect, and it finally creates both horizontal and vertical lift -- you don't need physical support to prevent the object from drifting sideways.
The technology only works with stationary objects at the moment. Sorry, folks, you won't see ultrasonic hovercars any time soon. Levitation that can manipulate large objects is on the cards, though, and it shouldn't be limited to specific shapes or sizes. You could eventually see this used to hold on to liquid in space, or to study very hot objects (say, molten metal) that you wouldn't dare touch.
