Sound wave 3Dvolution: Japanese scientists move objects using acoustic levitation

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Japanese scientists have been successful in moving an object in a three-dimensional space through a complex system of acoustic levitation, surpassing previous research endeavors that lifted the objects in two dimensions.

In order to move expanded polystyrene particles of 0.6 mm and 2  mm in diameter, the Japanese scientists at the University of  Tokyo and the Nagoya Institute of Technology had to place the  objects inside a complex set-up of four arrays of speakers.

Using a refinement of the existing technology of sound wave  management, bubbles, a screw and a tiny piece of wood were  airlifted and moved around in all direction within the  experiment’s confines.

“We considered extended acoustic manipulation whereby  millimeter-sized particles were levitated and moved  three-dimensionally by localized ultrasonic standing waves, which  were generated by ultrasonic phased arrays,” the study  stated.

The experiment machine is comprised of audio speakers capable  generating inaudible high frequencies sound waves that intersect  inside a restrained space. The waves then generate a   “moveable ultrasonic focal point,” frequency noise  greater than 20kHz, where crossover creates standing waves. Some  waves are kept in constant position, serving as a suspending  force, while other waves are used to support a floating object  jammed in the standing waves.

“Our manipulation system has two original features. One is  the direction of the ultrasound beam, which is arbitrary because  the force acting toward its center is also utilized. The other is  the manipulation principle by which a localized standing wave is  generated at an arbitrary position and moved three-dimensionally  by opposed and ultrasonic phased arrays,” the study said.

The practice of moving tiny objects acoustically along the fixed  axes is not new, but it was previously applied to 2D, starting  from 1975.

“The essence of levitation technology is the countervailing  of gravity. It is known that an ultrasound standing wave is  capable of suspending small particles at its sound pressure  nodes,” Yoichi Ochiai from University of Tokyo said.

Currently, acoustic levitators are used mostly in industry and  for researchers of anti-gravity effects such as at NASA.