Generation and application of sub-kilohertz oscillatory flows in microchannels

TL;DR

This paper introduces a simple, versatile method to generate sub-kilohertz oscillatory flows in microchannels using a speaker, enabling new microfluidic applications like inertial focusing and mixing.

Contribution

The authors develop a user-friendly technique to produce controllable oscillatory flows in microchannels by directly coupling a speaker to microfluidic tubing, allowing independent control of frequency and amplitude.

Findings

The method achieves frequencies from 10 to 1000 Hz and amplitudes from 10 to 600 μm.

Flow profiles match theoretical Stokes flow benchmarks.

Applications demonstrated include inertial focusing and mixing in microfluidics.

Abstract

We present a user-friendly and versatile experimental technique that generates sub-kilohertz sinusoidal oscillatory flows within microchannels. The method involves the direct interfacing of microfluidic tubing with a loudspeaker diaphragm to generate oscillatory flow in microchannels with frequencies ranging from $10-1000$ Hz and amplitudes ranging from $10 - 600 \ \mu$m. The speaker-based apparatus allows independent control of frequency and amplitude that is unique to the speaker's manufacturing specifications. The performance of our technique is evaluated by Fourier spectral analysis of oscillatory motion of tracer particles, obtained by particle tracking velocimetry, as well as by comparing oscillatory flow profiles against theoretical benchmarks such as Stokes flow in a square channel and Stokes' second problem near a solid boundary. Applications that utilize both the oscillatory flow and the associated steady rectified flows are demonstrated in prototypical microfluidic configurations. These include inertial focusing and mixing at low Reynolds numbers, respectively.