We show that Bessel-function acoustic pressure fields can be used to trap and controllably position microparticles. A circular, 16-element ultrasound array generates and manipulates an acoustic field within a chamber, trapping microparticles and agglomerates. Changes in the phase of the sinusoidal signals applied to the array elements result in the movement of the Bessel-function pressure field and hence the microparticles. This demonstrates ultrasonic manipulation analogous to holographic optical tweezers. The manipulation limits of the device are explained by the existence of unwanted resonances within the manipulation chamber.
Courtney, C. R. P., Drinkwater, B. W., Grinenko, A., Wilcox, P. D., Demore, C. E. M., & Cochran, S. (2013). Dexterous manipulation of microparticles using Bessel-function acoustic pressure fields. Applied Physics Letters, 102(12), . https://doi.org/10.1063/1.4798584