Equivalent fully coupled modeling and experimental validation of high-particle-concentration acoustofluidics

Acoustofluidic particle manipulation has attracted considerable interest in biomedical applications due to its non-contact and label-free characteristics. However, existing computational models for predicting particle motion in acoustofluidic systems mainly focus on single-particle behavior, often neglecting particle–particle interactions and the impact of particle distribution on the acoustic and flow fields at high concentrations. To address these limitations, we propose an equivalent fully coupled model for the acoustofluidic manipulation of highly concentrated particle suspensions. Utilizing a two-phase flow framework, the suspension is modeled as an equivalent continuous medium, enabling the calculation of the effective acoustic field and the prediction of the motion and spatial distribution of both phases. Full coupling among the acoustic, fluid, and particle fields is achieved through iterative parameterization. The model is employed to investigate the dynamics of particles both above and near the critical size, with experimental validation conducted in both regimes. The results underscore the necessity of fully coupled modeling under high-concentration conditions. Moreover, a novel focusing state is identified for particles near the critical size, and its underlying mechanism is thoroughly analyzed.