Micropumps Jie Su
Outline • Introduction • Different types of micropumps • Mechanic pump • Membrane pump • Diffuser pump • Non-Mechanic pump • Bubble pump • Electrohydrodynamic (EHD) pump • Summary
Introduction • Micropumps play a significant role in microfludical systems of MEMS. • Micropumps were started in middle 1980s. • Before 1990s, mechanical pumps were mainly studied. After 1990s, non-mechanical pumps were introduced. • Presently most micropumps aim to fluid pumping.
Mechanical Pump • In general, mechanical pump consists of moveable components, such as moveable valves, moveable membrane, moveable channel, etc. • Mechanical pump can be categorized into: • Membrane pump • Rotary pump • Diffuser pump
Membrane Pump • Membrane Pump often consists of two check valves and a chamber with moveable membrane. • By some mechanisms, membrane can be actuated to change the volume of chamber. • Because the check valve can be opened only in one direction, for each circle, some fluid will be moved from inlet to outlet.
Electrostatic Membrane Pump • Goodness: • Low power, good control of actuation and short response time. • Weakness: • High actuation voltage, small stroke. R. Zengerle et. al., MEMS’95
Pieozelectric Membrane Pump • Goodness: • Large actuation force, and short response time. • Weakness: • Low working frequency, small stroke. V. Lintel et al., Sensors and Actuators A, 1988, 15:p. 153-167
Thermopneumatic Membrane Pump • Goodness: • Large actuation force, low operating voltage. • Weakness: • Low driving frequency Lammerink, 1993; Lammerink, 1996
Shape Memory Alloy Driven Membrane Pump Suction State Pumping State • Goodness: Large pumping rate, high working pressure. • Weakness: Low driving frequency, low energy efficiency W.L., Benard, et. al., “A Titanium-Nickel Shape-Memory Alloy Actuated Micropump”, Proceedings of Transducers’97, vol. 1, pp.361-364
Rotary Pump • Magnetically driven • Magnetic stator and central pin are permalloy • Rotors were separately made and assembled into pump by hand (50 microns tall, 500 microns diameter). • Problems are the complex fabrication process and reliability. C.H. Ahn and M.G. Allen, “Fluid Micropumps Based on Rotary Magnetic Actuators”, MEMS’s 95, 1995, pp. 408-412
inlet outlet outlet inlet Q2 Q1 Q1 Q2 Volume decreasing Volume increasing Diffuser action Nozzle action Diffuser action Nozzle action Supplying Mode: |Q1|>|Q2| Pumping Mode: |Q1|<|Q2| Diffuser Pump • Difference between diffuser pump and membrane pump is that diffuser pump has no check valves. Instead, two diffusers are introduced. • Diffuser is a channel with a increasing cross –sectional area. When fluid flows in one way or the other, it will encounter different flow resistances caused by the diffuser.
Diffuser Pump • Except the difference between diffusers and valves, diffuser pump is similar with membrane pump. • Many mechanisms can be used to drive a diffuser pump. • Goodness: simple fabrication, free of valve fatigue. • Weakness: sensitive to bubbles, low operating pressure Stemme et al., 1993,
Non-Mechanical Pump • Without movable parts, non-mechanical pump is often much simpler than mechanical pump. • Non-mechanical pump includes: • EHD pump • Bubble pump • Other pumps
EHD Pump • EHD pump uses applied electric field to induce and drag charges in fluid. • Goodness: no moving parts, very simple fabrication process • Weakness: unsuitable for conductive fluid
flow + - + - + - positive ion + - + - + - flow A Planar EHD Pump Si-Hong Ahn, Yong-Kweon Kim, “Fabrication and experiment of a planar micro ion drag pump,” Sensors and Actuators A70 (1998) 1-5
Our Design of EHD Pump • Build the electrodes and channel on the same wafer. • Electrodes go across the sidewall, resulting in a higher efficiency.
Two Successive Pumping Photos Fluid Fluid
Simplest Pump: Bubble Pump • Goodness: simple • Weakness: low flow rate, and fluid will be overheated near the heater. T.K. Jun and C.-K. kim, J. Appl. Phys., Vol. 83, No. 11, 1998
Bubble Pump T.K. Jun and C.-K. kim, J. Appl. Phys., Vol. 83, No. 11, 1998
Summary • Many kinds of micropump are fabricated • No perfect micropump exists. Each micropump has its weakness and goodness. • More work need to be done.