Acoustical tweezers using single spherically focused piston, X-cut, and Gaussian beams

Area of Science:

• Acoustics
• Wave Physics
• Computational Physics

Background:

• Acoustic radiation force calculations are crucial for particle manipulation.
• Existing models are limited to specific size regimes (Rayleigh or ray acoustics).
• Focused acoustic beams present unique challenges for theoretical analysis.

Purpose of the Study:

• To derive novel partial-wave series expansions (PWSEs) for acoustic radiation force calculations.
• To develop analytical formulations applicable to a wide range of sphere-to-wavelength ratios.
• To investigate the influence of focused beam properties and sphere characteristics on acoustic forces.

Main Methods:

• Utilized Rayleigh-Sommerfeld diffraction integral and addition theorems for spherical wave functions.
• Applied Fresnel-Kirchhoff approximation for weakly focused beams (α ≤ 20°).
• Derived PWSEs for piston, X-cut, and Gaussian apodized beams.

Main Results:

• Developed expressions for acoustic radiation force applicable beyond Rayleigh and ray acoustics limits.
• Demonstrated validity for wavelengths significantly exceeding the radiator radius.
• Identified dependence of forces on sphere's elastic properties and axial distance, including negative trapping forces.

Conclusions:

• The derived PWSEs offer a versatile tool for acoustic radiation force computation.
• The model accurately predicts forces for focused beams, overcoming limitations of prior analytical methods.
• Findings support applications in advanced acoustic manipulation, such as single-beam acoustical tweezers and levitation.