Acoustic Levitation

The ultrasonic chessboard could someday be used for delicate chemical or pharmaceutical processes where contamination from a surface could spoil the reaction, said Dimos Poulikakos, an engineer at Switzerland‘s ETH Zurich. What‘s new about the device that he and his colleagues constructed is that it uses a chessboard-like array of levitating devices to transport objects through the air with ultrasound. The research team made droplets of water and hydrocarbons ! oat around the squares of the array and smash into each other. Each of the squares in the chessboard is an acoustic resonator, sending out sound waves at 24.3 kilohertz so that it’s reflected off a precisely placed sheet of transparent plastic. The frequency is too high to be heard by human ears. But even at that frequency, the acoustic interference can be strong enough to create a standing wave between the resonators and the reflector, counteracting gravity’s pull on the target object. The levels on each of the resonators can be adjusted to transport an object from one of the squares on the chessboard to the next one over. The theoretical size limit for the device depends on the substance being levitated as well as the acoustic frequency. For a drop of water at 24 kilohertz, it‘s about a tenth of an inch (2.7 millimeters). But that‘s big enough for pharmaceutical applications, or even for applications that involve manipulating hazardous chemical or radioactive ingredients.

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