Multitarget manipulation of off-axis acoustic vortices based on a focused sector-vortex transducer array

The acoustic vortex (AV) offers a noncontact, label-free, and high-precision manipulation technology for particles and cells, holding promising application aspects in the fields of biology, chemistry, engineering, and medicine. However, the flexible multitarget manipulation is still constrained by the large array of transducers or the fixed structure of the holographic plate. In this study, a phase-controlled multiple off-axis focused AVs (OA-FAVs) approach with strengthened trapping capability and flexibility is developed based on a focused sector-vortex transducer array. By introducing additional phase shifts to sectorial sources based on the preset radial offsets in the focal plane, the multitarget manipulation is realized by OA-FAVs based on the multiplexing technology. It is proved that the maximum number of OA-FAVs is half of the element number of the sector-vortex array. The high-pressure annulus with a phase spiral of OA-FAV deteriorates gradually with an increase in the radial offset, and the maximum offset of OA-FAV that maintains the main characteristics of the vortex pattern is approximately 3.1 times the wavelength. The performance of the independent multitarget trapping, which is superior to traditional AVs, is demonstrated by the acoustic gradient force in both axial and radial directions. By utilizing the accurate phase control for an eight-element sector-vortex array, composite fields of OA-FAVs are measured, and the stable rotational trappings of two, three, and four polyethylene particles are conducted successfully in the experiment. The multitarget manipulation of OA-FAVs provides a new possibility for the real-time manipulation of multiple objects using a unilateral focused sector-vortex array with significantly improved efficiency and flexibility, exhibiting prosperous perspectives in particle manipulation and cell assembly as well as acoustic printing in biomedical applications.