Seah, S. A., Drinkwater, B. W., Carter, T., Malkin, R., & Subramanian, S. (2014). Dexterous ultrasonic levitation of millimeter-sized objects in air. IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, 61(7), 1233–1236. http://doi.org/10.1109/TUFFC.2014.3022
Acoustic levitation in air has applications in contactless handling and processing. Here a first-order Bessel function-shaped acoustic field, generated using an 8-element circular array operating at 40 kHz, traps millimeter-sized objects against gravity. The device can manipulate objects in a vertical plane over a few millimeters with an accuracy of ± 0.09 mm.
A 1.5mm diameter Expanded PS sphere being positioned by the array. The red dots are the target positions and the green dots are the achieved positions.