Acoustic dipole and monopole effects in solid particle interaction dynamics during acoustophoresis

Area of Science:

• Acoustics
• Microfluidics
• Particle Physics

Background:

• Acoustic radiation forces are crucial in microfluidic particle manipulation.
• Understanding secondary forces between particles is essential for precise control.
• Existing models may not fully capture complex particle interactions in ultrasonic fields.

Purpose of the Study:

• To present a method for measuring secondary acoustic radiation forces on solid particles.
• To investigate particle-particle interaction dynamics in ultrasonic standing waves.
• To analyze the influence of particle properties and arrangement on interaction forces.

Main Methods:

• Utilizing a novel method to measure secondary acoustic radiation forces.
• Employing a theoretical model considering density- and compressibility-dependent effects.
• Conducting experiments with two distinct sizes of polystyrene micro-particles (4.8 and 25 μm) in a 2-MHz ultrasonic standing wave within a microfluidic channel.

Main Results:

• Observed deflections in particle pathways indicate significant interaction forces.
• Particle interaction forces are non-negligible and must be considered in particle manipulation.
• Interaction effects are most pronounced for closely spaced, differently sized particles with distinct acoustic properties relative to the medium.
• Observed forces are influenced by the angle between the inter-particle centerline and the standing wave propagation axis, aligning with theoretical predictions.

Conclusions:

• The presented method enables accurate measurement of secondary acoustic radiation forces.
• Particle-particle interactions significantly affect manipulation outcomes in acoustophoresis.
• Accurate particle manipulation requires consideration of these secondary forces, especially in applications involving multiple particles with varying characteristics.