Researchers from the University of Sao Paulo in Brazil have developed a levitation system that allows a small object to hover with more control than was previously possible. The system can levitate polystyrene particles by reflecting sound waves from a source off a concave reflector below. Changing the orientation of the reflector also allows the hovering particle to be moved around. Other such devices have previously been built, but they have required a precise setup where the sound source and reflector were at fixed resonant distances, which limited the amount of control over the levitating object. The new system demonstrates the possibility of a non-resonant levitation device; meaning, one that does not require a fixed separation distance between the source and the reflector. This may be a step towards larger systems that could be used to handle hazardous materials or chemically sensitive materials. The researchers tested the device with polystyrene about 3 mm across. The next step is to improve the device to levitate heavier materials. Typically, the system consists of an upper cylinder that emits high-frequency sound waves that, when they hit the concave part of the device at the bottom, are reflected back. The reflected waves interact with newly emitted waves to produce standing waves, which have minimum acoustic pressure points. If the acoustical pressure at these nodes is strong enough, it can counteract the force of gravity. In the new system, the distance between the sound emitter and the reflector can be continually changed without affecting the levitation performance. They researchers also showed that levitating particles can be manipulated by controlling the reflector position while maintaining the transducer in a fixed position.
Source: AIP
