Effective mixing of laminar flows at a density interface by an integrated ultrasonic transducer

Abstract

An acoustic mixer for glass channel microfluidic systems is presented. An acoustic standing wave, perpendicular to the fluid flow, is generated by the excitation of a miniaturized piezoelectric transducer operated around 10 MHz. The transducer is fabricated into a planar printed circuit board structure, constituting the bottom channel wall, which makes the mixer simple to integrate with a wide selection of microfluidic channel designs. The mixing occurs at a fluid-fluid density interface due to the acoustic radiation force; an analytical expression is derived to qualitatively describe this phenomenon. Only a small density difference in the range of 2-5% is required to achieve 150-270% peak broadening of a fluorescent sample between sheath flows, which we use as a measure of the mixing efficiency. The mixing efficiency is measured with regard to its sensitivity to the density difference, the fluid velocity and the transducer driving frequency. Transducers at different positions along the microchannel make it possible to compare the mixing of straight versus diagonal flows across the transducer surface. We finally demonstrate enhanced chemical lysis of E. coli K12 cells in the device due to active fluid mixing.

An integrated acoustic and dielectrophoretic particle manipulation in a microfluidic device for particle wash and separation fabricated by mechanical machining

“…It was reported in literature that acoustic radiation forces may cause mixing at the interface of fluids with different acoustic impedances. 43,44 In our case however, the difference of acoustic impedances of the fluids flowing from the center and the side inlet is less than 0.13%, which points out that mixing is not likely due to acoustic mixing but rather due to the diffusion of the ions inside the channel in the wash unit. Moreover, carried high conductivity fluid (i.e., low resistance) by the particles into the low-conductivity stream (i.e., high resistance) also contributes to the deviation of the result from the ideal case.…”

On-Chip Fluorescence-Activated Cell Sorting by an Integrated Miniaturized Ultrasonic Transducer

“…32 Particles present in any of the fluids adjacent to the density interface will move with the flow motion. A density difference in the range of a few percent (> 2 %) is required between the shuffle flow and the sample flow to generate effective fluid motion sufficient for cell sorting purposes.…”

“…A density difference in the range of a few percent (> 2 %) is required between the shuffle flow and the sample flow to generate effective fluid motion sufficient for cell sorting purposes. The primary acoustic radiation force acting on a fluid interface, 36 ( )…”

A highly uniform lamination micromixer with wedge shaped inlet channels for time resolved infrared spectroscopy

“…A simple electromagnetically actuated micromixer was presented by Wen et al (2009) with mixing times in the 1 s range. Designs utilizing acoustic waves achieved mixing times down to 7 ms (Ahmed et al 2009;Johansson et al 2009). Another active mixing principle with an actuated cantilever in the mixing channel was investigated by Williams et al (2009) without stating actual mixing times.…”