High-frequency single-beam acoustic tweezers: A numerical investigation of drag and radiation forces.

Single-beam acoustic tweezers (SBAT) use focused ultrasounds to remotely hold, move, and apply forces to objects in three dimensions. Addressing potential applications in the microscopic range requires a high frequency, since the object size scales with the acoustic wavelength. Acoustic streaming, the fluid motion induced by the acoustic attenuation of ultrasonic waves, can generate a drag force that opposes the acoustic radiation force, complicating stable manipulation. This study investigates the interplay between acoustic radiation force and the streaming-induced drag force under sharp focusing conditions for the feasibility of high-frequency SBAT. Using theoretical modeling and numerical simulations, this study examines how acoustic pressure amplitude, beam focusing, and frequency affect streaming flow and trapping stability. The results provide insights into optimizing high-frequency SBAT systems, especially in liquid environments, and should contribute to improving the precision and reliability of acoustic manipulation at the micro-scale.