Reconfiguring Surface Acoustic Wave Microfluidics via In Situ Control of Elastic Wave Polarization.

Area of Science:

• Physics
• Microfluidics
• Materials Science

Background:

• Surface Acoustic Waves (SAW) are typically designed to generate vertically polarized Rayleigh waves.
• Conventional SAW devices are limited in their ability to manipulate particles and cells dynamically.
• Understanding and controlling wave polarization in SAW devices is crucial for advanced microfluidic applications.

Purpose of the Study:

• To demonstrate in-situ control of elastic wave polarization in SAW devices.
• To develop highly reconfigurable SAW microfluidics capable of switching between acoustohydrodynamic (AHD) and electrohydrodynamic (EHD) regimes.
• To explore novel particle manipulation mechanisms and colloidal assembly dynamics.

Main Methods:

• Experimental and theoretical identification of an unexpected shear-horizontal (SH) wave mode in a conventional Rayleigh (R) wave design.
• Selective excitation of both SH and R wave modes for controlled polarization.
• Integration of AHD and EHD regimes within a single SAW microfluidic platform.

Main Results:

• Achieved selective excitation of predominantly horizontally polarized SH waves alongside vertically polarized R waves.
• Demonstrated on-demand reconfiguration between AHD and EHD regimes for particle manipulation.
• Observed unprecedented colloidal patterns and dynamics, including a novel diamond-shaped assembly in the EHD regime due to a virtual zero-boundary electric quadrupole.

Conclusions:

• The in-situ control of SAW polarization revolutionizes understanding of acoustofluidics.
• This work expands the potential of SAW microfluidics by enabling on-demand advantages of both AHD and EHD regimes.
• The findings inspire new strategies for micro- and nanoscale manufacturing and manipulation with broad applications.