Modeling of microdevices for SAW-based acoustophoresis --- a study of boundary conditions

TL;DR

This study uses finite-element modeling to compare full solid-fluid and simplified reduced models of SAW-based acoustophoresis devices, revealing limitations of reduced models especially for soft elastomer walls like PDMS.

Contribution

It introduces detailed finite-element models for microfluidic devices and evaluates the accuracy of simplified boundary condition models in different material contexts.

Findings

Reduced models approximate pyrex systems well at large wall thicknesses.

Reduced models poorly approximate PDMS systems, especially with thin walls.

Full models highlight significant differences in acoustic fields based on boundary conditions.

Abstract

We present a finite-element method modeling of acoustophoretic devices consisting of a single, long, straight, water-filled microchannel surrounded by an elastic wall of either borosilicate glass (pyrex) or the elastomer polydimethylsiloxane (PDMS) and placed on top of a piezoelectric transducer that actuates the device by surface acoustic waves (SAW). We compare the resulting acoustic fields in these full solid-fluid models with those obtained in reduced fluid models comprising of only a water domain with simplified, approximate boundary conditions representing the surrounding solids. The reduced models are found to only approximate the acoustically hard pyrex systems to a limited degree for large wall thicknesses and not at all for the acoustically soft PDMS systems.