Acoustical pulling force of a limited-diffracting annular beam centered on a sphere.

Area of Science:

• Acoustics
• Wave physics
• Particle manipulation

Background:

• Acoustic radiation force (ARF) is typically repulsive.
• Contactless manipulation of particles is crucial in various scientific fields.
• Limited-diffracting beams offer extended axial depth-of-field for acoustic applications.

Purpose of the Study:

• To investigate the generation of a negative (attracting) acoustic force using a specific transducer geometry.
• To analytically derive the acoustic fields and radiation force without approximations.
• To explore conditions for achieving an axial ARF directed towards the source.

Main Methods:

• Utilized the Rayleigh-Sommerfeld diffraction integral and addition theorems for spherical wave functions.
• Derived exact closed-form partial-wave series expansions for incident and scattered acoustic fields.
• Evaluated time-averaged acoustic radiation force on a sphere in a nonviscous fluid.

Main Results:

• Identified conditions where a pulling axial ARF arises, directed towards the annular ring-source.
• Demonstrated that transducer radial thickness, sphere-source distance, transducer size, and sphere properties influence ARF.
• Achieved an exact solution for acoustic fields and ARF without approximations.

Conclusions:

• The annular-ring transducer geometry enables the generation of attractive acoustic forces.
• This method provides a reliable solution for contactless particle manipulation with extended axial control.
• The findings have widespread applications in designing acoustic tweezers and microfluidic devices.