Microfluidic mixer and transporter based on PZT self-focusing acoustic transducers

This paper describes noninvasive acoustic micromixer and transporter as well as a microfluidic subsystem (on a single silicon chip) based on the two microfluidic actuators. The actuators use a piezoelectric PZT sheet to generate about 10-12.5MHz acoustic waves (corresponding to the PZT thickness), an array of sectored Fresnel annular rings [for the electrodes sandwiching the piezoelectric transducer (PZT)] to self-focus the acoustic waves, and acoustic streaming effect to produce a body force for fluidic motion. The self-focused waves from the PZT array propagate through 200-μm-thick silicon without any significant energy loss, and move the liquid contained in the channels and chambers (without a cover) on a micromachined silicon chip, up to 123 mm/s in-plane speed. The PZT array (consisting of a PZT sheet with an array of electrode patterns for sectored Fresnel rings) is bonded to the micromachined silicon chip to produce a fast in-plane liquid motion in the open channels and chambers. When the liquid motion is produced in a channel, we have a liquid transporter; while when the motion is produced in a large area chamber, we have a micromixer. Various channel and chamber structures have been fabricated to verify the efficacies of the liquid transport and mixing. A microfluidic subsystem integrating a micromixer, transporters and reservoirs has been shown to transport two types of liquids from their reservoirs to a mixer and to mix the liquids together within 2 s. The experimental results agree well with theoretical studies and simulation results.