Strategies for Microparticle Manipulation by Rectified Inertial Forces

Oscillating interfaces in a liquid give rise to inertial effects that manifest as multiple physical phenomena on slower (steady) time scales, including streaming flow and force actuation on immersed particles. While these effects have traditionally been treated separately, we develop a timescale separation formalism that puts streaming motion of fluid elements and rectified motion of particles on the same footing.
Using ultrasound-driven microbubble oscillations in microfluidic devices allows for flexible and specific manipulation of particles: depending on parameters, microparticle reaction is selective by size or by density, results in attraction to or repulsion from the bubble, and can be focused on particle trapping or deflection. Thus, a device can be tailored to desired applications by changing easily controlled parameters like flow speed and driving frequency.