# Three-dimensional numerical modeling of surface acoustic wave devices: Acoustophoresis of micro- and nanoparticles including streaming

## TL;DR

This paper introduces a comprehensive 3D numerical model for surface acoustic wave devices, capturing electromechanical, acoustic, and streaming effects to better understand and optimize acoustofluidic particle manipulation.

## Contribution

It presents the first fully 3D simulation including electromechanical, acoustic, and streaming effects, validated against experimental data for SAW microfluidic devices.

## Key findings

- Accurately predicts acoustic resonances and particle responses.
- Explains differences between soft and hard lid device behaviors.
- Reproduces observed streaming flow patterns.

## Abstract

Surface acoustic wave (SAW) devices form an important class of acoustofluidic devices, in which the acoustic waves are generated and propagate along the surface of a piezoelectric substrate. Despite their wide-spread use, only a few fully three-dimensional (3D) numerical simulations have been presented in the literature. In this paper, we present a 3D numerical simulation taking into account the electromechanical fields of the piezoelectric SAW device, the acoustic displacement field in the attached elastic material, in which the liquid-filled microchannel is embedded, the acoustic fields inside the microchannel, as well as the resulting acoustic radiation force and streaming-induced drag force acting on micro- and nanoparticles suspended in the microchannel. A specific device design is presented, for which the numerical predictions of the acoustic resonances and the acoustophoretic repsonse of suspended microparticles in 3D are successfully compared with experimental observations. The simulation provides a physical explanation of the the observed qualitative difference between devices with an acoustically soft and hard lid in terms of traveling and standing waves, respectively. The simulations also correctly predict the existence and position of the observed in-plane streaming flow rolls. The presented simulation model may be useful in the development of SAW devices optimized for various acoustofluidic tasks.