Trapping of sub-wavelength microparticles and cells in resonant cylindrical shells

Acoustic tweezers based on the focused field hold the promise of contactless manipulation of microparticles. However, acoustic diffraction severely limits the trapping strength and the minimum size of the trapped particles in conventional diffraction-limited systems. Here, we propose and demonstrate a simple cylindrical shell structure for the trapping of microparticles with a radius as small as 1/400 of the corresponding acoustic wavelength, and its trapping ability is much stronger than that of the standing wave. This mechanism is attributed to the significantly enhanced acoustic radiation force originating from the resonant excitation of low order circumferential modes intrinsically existing in the cylindrical shell, which is a highly localized field around its surfaces. Cylindrical shell-based acoustic tweezers are simple, disposable, low cost, biocompatible, and functional, which may be of interest for nano-scale manufacturing and biomedical applications such as bio-printing, cell culturing, and tissue engineering.