Sorting of liquid metal particles in microchannels under surface acoustic waves actuation

The excellent electrical and thermal conductivity of eutectic gallium–indium (EGaIn) particles makes them attractive materials for flexible and wearable electronics. However, conventional synthesis methods inevitably produce particles with a broad size distribution. Therefore, efficient size-based sorting is required for practical applications. In this study, the effects of acoustic field parameters and inlet flow velocity ratios on the sorting of EGaIn particles driven by surface acoustic waves are investigated. It is found that increasing the inclination angle of the acoustic field induces a transition in particle motion from a continuous mode to an intermittent mode. The influence of acoustic pressure on particle sorting is found to depend strongly on particle diameter. As the acoustic pressure increases, the motion of 10 and 15 μm particles transitions from an intermittent to a continuous mode, accompanied by an increase in lateral deflection that reaches a maximum and then saturates. By contrast, 20 μm particles remain in the continuous motion mode, with their lateral deflection remaining at its maximum value over the entire range of acoustic pressures considered. Numerical simulations show that, at an acoustic pressure of 0.2 MPa and an inclination angle of 2°, particles of different diameters can be separated by tuning the inlet flow velocity ratio. For particle sorting at high concentrations, dynamic adjustment of parameters such as flow velocity, inclination angle, acoustic frequency, and acoustic pressure is required to maintain a high recovery rate.