Ž . Sensors and Actuators 77 1999 229–236 www.elsevier.nlrlocatersna Design and optimization of an ultrasonic flexural plate wave micropump using numerical simulation N.T. Nguyen a, ) , R.M. White b a School of Mechanical and Production Engineering, Nanyang Technological UniÕersity, Nanyang AÕenue, Nanyang 639798, Singapore b Berkeley Sensor and Actuator Center, EECS, UniÕersity of California Berkeley, Berkeley, CA 94720, USA Received 8 June 1998; accepted 13 April 1999 Abstract This paper presents design issues and a numerical model of a micromachined pump based on acoustic streaming in water. Influences of channel height, wave amplitude, and backpressure on the velocity profile and flow rate are investigated. Using these results, design rules for the acoustic micropump are derived. Thermal transport effects of the acoustic streaming are also discussed in order to integrate a thermal flow sensor into the pump or to apply the pump for cooling purposes. q 1999 Elsevier Science S.A. All rights reserved. Keywords: Micropump; Microfluidics; Acoustic streaming 1. Introduction In recent years, microfluidic devices have been emerg- ing as an important product of the microsystem technol- ogy. Microfluidic devices may be employed in chemical and microbiological analysis, in order to reduce analysis time and required sample volumes. Micropumps are signif- icant components for delivering samples in such micro- analysis systems. Therefore, micropumps have become a ‘hot’ topic of microfludics research. Several review papers have shown diverse micromachined pumping principles w x 1–3 . Micromachined pumps can be classified by actuat- Ž ing principles piezoelectric, pneumatic, thermopneumatic, . Ž thermomechanic, electrostatic or pump principles re- ciprocating, peristaltic, electrohydrodynamic, electroos- . motic, ultrasonic . Most reported pumps are based on the use of passive valves or diffuserrnozzle elements. Since most of these principles are based on the viscous flow, the high fluidic impedance of micromachined channel systems should be seriously considered. Using the so-called ‘ac- tive’ channel is a possible solution of the impedance problem. A ‘active’ channel can transport liquid and gases by itself. Electrohydrodynamic pumping with travelling wave potentials, and the ultrasonic pumping reported in this paper belong to this channel type. ) Corresponding author. E-mail: namtrungnguyen@yahoo.com Several recent publications have concerned flexural plate Ž . w x wave FPW devices for pumping liquids or gases 4–6 . The pumping is based on the phenomenon of acoustic streaming. When a flexural wave propagates in a thin membrane, a high intensity acoustic field appears in the fluid near the membrane. This acoustic field causes fluid flow in the direction of wave propagation. The first-order particle velocity varies as an exponential function. Thus, only a fast moving fluid layer exists close to the mem- brane. The basic FPW-device is shown in Fig. 1. This device consists of rectangular flow channel that has a thin membrane on the bottom. The composite membrane is made of low-stress silicon nitride, piezoelectric zinc oxide, and aluminum. Typical membrane thicknesses range from 1 to 3 mm. The FPW have a typical frequency of 3 MHz and a wavelength of 100 mm. Interdigitated transducers Ž . IDTs , arrays of finger pairs placed at wavelength inter- vals on the piezoelectric film, generate the flexural waves. The FPW-studies referenced above are limited to ana- lytical models and experimental observations. Because of the complexity of the acoustic streaming and the pumping effect, a systematic design and optimization of acoustic micropumps is only possible with numerical models. Also, the published works concentrated only on the mass trans- port caused by acoustic streaming, and did not investigate its effects for thermal transport. This paper presents a numerical investigation for under- standing the principle of acoustic streaming and a system- 0924-4247r99r$ - see front matter q 1999 Elsevier Science S.A. All rights reserved. Ž . PII: S0924-4247 99 00216-2