Abstract: Contactless manipulation of multi-scale objects using the acoustic vortex (AV) tweezers offers tremendous perspectives in biomedical applications. However, it is still hindered by the weak acoustic radiation force (ARF) and torque (ART) around the vortex center. By introducing the elevation angle to the planar transducers of an N-element ring array, the weak-focused acoustic vortex (WFAV) composed of a main-AV and N paraxial-AVs is constructed to conduct a large-scale object manipulation. Different from the traditional focused AV (FAV) generated by a ring array of concave spherical transducers, a much larger focal region of the WFAV is generated by the main lobes of the planar transducers with the size inversely associated with the elevation angle. With the pressure simulation of the acoustic field, the capability of the rotational object driving in the focal plane for the WFAV is analyzed using the ARF and the ART exerted on an elastic ball based on acoustic scattering. With the experimental system built in water, the generation of the WFAV is verified by the scanning measurements of the acoustic field and the capability of object manipulation is also analyzed by the rotational trapping of floating particles in the focal plane. The favorable results demonstrate the feasibility of large-scale rotational manipulation of objects with a strengthened ART and a reduced acousto-thermal damage to biological tissues, showing a promising prospect for potential applications in clinical practice.

Key words: acoustic vortex, weak-focused, large-scale object manipulation, acoustic scatter, acoustic radiation force