Acoustic rotational manipulation using orbital angular momentum transfer.

Area of Science:

• Acoustics and Fluid Dynamics
• Physics of Sound
• Material Science

Background:

• Acoustic orbital angular momentum (OAM) offers unique manipulation capabilities.
• Transferring OAM to absorbing materials in viscous media is challenging.
• Understanding acoustic-fluid interactions is crucial for advanced applications.

Purpose of the Study:

• To quantitatively test acoustic OAM transfer to a sound-absorbing object in a viscous liquid.
• To investigate the balance between acoustic radiation torque and viscous torque.
• To explore novel acoustic streaming phenomena induced by OAM transfer.

Main Methods:

• An original experiment using an ultrasonic vortex beam to spin a millimeter-size target disk.
• Calculation of acoustic radiation torque using the Brillouin stress tensor.
• Evaluation of viscous torque from the steady-state spinning frequency.

Main Results:

• Demonstrated a balance between calculated acoustic radiation torque and experimentally determined viscous torque.
• Unveiled a rotational acoustic streaming phenomenon.
• Showed that acoustic streaming reduces viscous torque, aiding torque balance.

Conclusions:

• The study provides the first quantitative test of acoustic OAM transfer to absorbing objects in viscous liquids.
• Acoustic streaming driven by OAM transfer plays a significant role in fluid dynamics.
• This research opens avenues for acoustic manipulation in complex fluids.