Mechanistic investigation of particle separation in standing-wave acoustofluidic microchannels

Abstract

Microparticle separation has become a powerful label-free detection technique. This study presents a microfluidic particle separation method based on acoustic standing waves. A multiphysics coupled model integrating acoustic fields, laminar flow, and particle tracing was developed to characterize particle migration and separation behaviors under the combined action of acoustic and hydrodynamic fields. We systematically investigate the effects of acoustic field parameters, hydrodynamic conditions, and particle material properties on particle separation. The results reveal that particle migration is governed by acoustic radiation forces and hydrodynamic transport. Under the optimized operating conditions, the numerical model achieved complete size-selective separation of 1, 5, and 10 μm particles, corresponding to 100% separation efficiency and 100% separation purity. Enhanced acoustic excitation promotes transverse displacement, whereas flow regulation alters streamline distributions and outlet collection regions, thereby influencing particle redistribution. Distinct separation behaviors are observed under different acoustofluidic conditions, resulting in under-migration, stable separation, or excessive lateral displacement. In addition, particle material properties significantly affect separation trajectories and outlet distributions because of differences in the acoustic contrast factor. Particles with moderate acoustic contrast achieve optimal confinement, while weak or strong responses compromise separation performance. This study demonstrates that effective separation can be achieved through coordinated control of acoustic and hydrodynamic effects. These findings provide mechanistic insights into standing-wave acoustofluidic separation and offer guidance for the design and optimization of acoustofluidic devices.