Numerical investigation of particle deflection in tilted-angle standing surface acoustic wave microfluidic devices

The tilted-angle standing surface acoustic wave (taSSAW) microfluidic device has become a powerful tool for biosample separation due to its biocompatibility and non-contact, label-free, and high-efficiency nature. Studying and modeling particle deflection in a microfluid environment containing a taSSAW field is essential in the design of robust taSSAW-based microfluidic devices. Here, we present a numerical model taking into consideration fluid viscous drag force and the acoustic radiation force induced by scattering of acoustic waves for the study of particle deflection. The reliability of the model is validated by comparing our predictions with data from existing literature. In order to support our prediction experimentally, we fabricated a taSSAW microfluidic chip using 128° YX LiNbO₃, and the deflection results for 3- and 7-μm polystyrene microspheres concur with the numerical estimation. The effects on particle deflection by parameters such as pre-focusing, pre-focusing width, average flow velocity, acoustic pressure amplitude, tilted angle, and surface acoustic wave frequency on particle deflection are then analyzed. This model could be used to optimize the design and better understand the mechanism of taSSAW microfluidic devices.