Negative axial radiation forces on solid spheres and shells in a Bessel beam.

Area of Science:

• Acoustics
• Fluid Dynamics
• Materials Science

Background:

• Acoustic radiation force typically propels objects along the direction of wave propagation.
• Prior theoretical work suggested negative acoustic radiation force for fluid spheres under specific conditions.

Purpose of the Study:

• To extend the prediction of negative acoustic radiation force to solid and hollow spherical objects.
• To investigate the acoustic scattering patterns associated with negative radiation force.

Main Methods:

• Numerical computations were performed to simulate the interaction of acoustic Bessel beams with spherical targets.
• Angular scattering patterns were analyzed for solid poly(methylmethacrylate) (PMMA) spheres and empty aluminum spherical shells in water.

Main Results:

• The study confirmed the possibility of negative acoustic radiation force for a solid PMMA sphere and an empty aluminum spherical shell in water.
• Acoustic scattering into the back hemisphere was observed to be suppressed when the radiation force was negative, differing from plane wave illumination patterns.

Conclusions:

• The findings support the potential for acoustic Bessel beams to generate forces opposing wave propagation for various spherical objects.
• This research contributes to the development of acoustic tweezers and novel methods for object manipulation in space environments.