Modeling of Microdevices for SAW-Based Acoustophoresis — A Study of 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 but not very well for acoustically soft PDMS systems shorter than the PDMS damping length of 3 mm.

Keywords

• microdevices
• acoustofluidics
• surface acoustic waves
• numeric modeling
• hard wall
• lossy wall
• polydimethylsiloxane (PDMS)
• borosilicate glass (pyrex)