Generation and application of sub-kilohertz oscillatory flows in microchannels

We present an accessible and versatile experimental technique that generates sub-kilohertz sinusoidal oscillatory flows within microchannels. This method involves the direct interfacing of microfluidic tubing with a loudspeaker diaphragm, which allows independent control of oscillation frequency and amplitude. Oscillatory flows were generated with frequencies ranging from 10 to 1000 Hz and amplitudes ranging from 10 to 600μm. Fourier spectral analysis of particle trajectories, obtained by particle tracking velocimetry, was used to evaluate the oscillatory displacement in microchannels and shown to accurately represent simple harmonic motion specified by the loudspeaker. Oscillatory flow profiles in microchannels of square and rectangular cross-sections were characterized as a function of oscillation frequency, or Womersley number, and compared to theoretical benchmarks, such as Stokes flow and Stokes’ second problem. To highlight the versatility and effectiveness of the experimental method, prototypical applications were demonstrated utilizing pulsatile flow in microfluidic devices, such as inertial focusing and enhanced mixing at low Reynolds numbers.