Ultrasonic 'tube' of sound levitates and guides matter through air

Researchers at the University of Helsinki, with partners in Spain and the US, demonstrated a prototype acoustic tube: 256 miniature transducers at 40 kHz confine and steer liquids, gases, powders and even plasma without physical walls. The 8 cm device draws about 50 W, and the work was published in PNAS.

• 256 ultrasonic transducers at 40 kHz form an invisible 8 cm tube
• Prototype guides water, powders, mist, gas and electrical discharges
• Draws about 50 W; sound is above the human hearing range
• Flow direction is changed electronically without moving parts