Active micromixers - Micromixers Fundamentals Design and Fabrication - page 287

FIGURE 7.38
The concept of acoustic streaming: (a) wave propagation in a flexible membrane; (b) pressure field in the fluid,
positive and negative pressures are indicated; (c) the first order velocity; (d) the second order or net velocity of
acoustic streaming.

150 m thick and covers the entire mixing chamber. The titanium/platinum layer was deposited on

the silicon membrane before gluing the PZT layer. The piezodisc was driven by a square wave
(50 V peak-to-peak, 60 KHz).
Jang et al. [50] report a similar micromixer with a circular mixing chamber. The chamber measures
6 mm in diameter and 30

m

m in depth. The chamber was wet etched in KOH and sealed to a Pyrex
glass wafer by anodic bonding. A 6 mm

m

6 mm rectangular piezoelectric layer is glued to the
membrane above the chamber. The bimorph of 190

m m-thick (lead-zirconate-titanate) PZT layer and

210 m-thick silicon membrane forms the actuator for the mixing chamber. The mixer operated at

resonant frequencies of the first three modes. The mixing pattern of the first two modes is depicted in
Fig. 7.37 . The higher the frequency the better is the mixing because of the faster induced acoustic

m