Scaling acoustic vortex traps with topological charge

Three-dimensional trapping of Mie particles using acoustic vortices has been demonstrated through experimental studies leveraging metasurfaces and transducer arrays. While extensive analytical and numerical studies have explored the properties and dimensions of vortex beams, a comprehensive investigation into the dependence of trap size, stability, and positioning on the focused vortex's topological charge remains lacking. This study presents an analytical, numerical, and experimental analysis of focused vortex particle trapping generated by a plane wave transducer equipped with a phase-modifying metalens. Our results reveal a strong linear dependence of the trap size on the topological charge, aligning with trends previously observed for Gaussian and optical vortex beams. This finding is experimentally validated using a piezoelectric transducer and a custom silicone lens to generate focused vortex beams, successfully trapping polymer particles of varying sizes in a water-filled chamber. Additionally, numerical and experimental data confirm the analytical prediction that increasing the beam's topological charge shifts the trap position closer to the acoustic source. These results establish crucial design principles for acoustic trapping applications, particularly in biomedical and particle manipulation technologies.