Micropumps/Microvavles

Outline

Different types of micropumpsMechanic pump

Membrane pumpDiffuser pump

Non-Mechanic pumpBubble pumpElectrohydrodynamic (EHD) pump

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• Micro gear pump• Diffuser pump

Pump chamber

Valves

Check valve-example

Fixed geometry valve 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

R. Zengerle et. al., MEMS’95

• Goodness:

Low power, good control of actuation and short response time.

• Weakness:

High actuation voltage, small stroke.

Pieozelectric Membrane Pump

V. Lintel et al., Sensors and Actuators A, 1988, 15:p. 153-167

• Goodness:

Large actuation force, and short response time.

• Weakness:

Low working frequency, small stroke.

Lammerink, 1993; Lammerink, 1996

Thermopneumatic Membrane Pump

• Goodness:

Large actuation force, low operating voltage.

• Weakness:

Low driving frequency

Suction State Pumping State

W.L., Benard, et. al., “A Titanium-Nickel Shape-Memory Alloy Actuated Micropump”, Proceedings of Transducers’97, vol. 1, pp.361-364

Shape Memory Alloy Driven Membrane Pump

• Goodness: Large pumping rate, high working pressure.

• Weakness: Low driving frequency, low energy efficiency

Centrifugal pump- 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

Micro gear pump

Diffuser Pump

inlet outlet

Diffuser action Nozzle action

Q1 Q2

Supplying Mode: |Q1|>|Q2|

Volumeincreasing

inlet outlet

Diffuser action Nozzle action

Q1Q2

Pumping Mode: |Q1|<|Q2|

Volumedecreasing

• 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.

• 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,

Diffuser Pump

Non-Mechanical Pump

• Without movable parts, non-mechanical pump is often much simpler than mechanical pump.

• Non-mechanical pump includes:• Electric field mediated pump• Bubble pump• Other pumps

Electric field mediated pump

Electric-osmotic pump

Electric-osmotic pump-example

Static EHD pump

EHD pump-example

EHD Pump

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

EHD PUMP-example

A Planar EHD Pump

+ - + - + -

flow

positive ion

+ - + - + -

flow

Si-Hong Ahn, Yong-Kweon Kim, “Fabrication and experiment of a planar micro ion drag pump,” Sensors and Actuators A70 (1998) 1-5

Design of EHD Pump

1. Build the electrodes and channel on the same wafer.

2. Electrodes go across the sidewall, resulting in a higher efficiency.

Two Successive Pumping Photos

FluidFluid

Simplest Pump: Bubble Pump

T.K. Jun and C.-K. kim, J. Appl. Phys., Vol. 83, No. 11, 1998

• Goodness: simple

• Weakness: low flow rate, and fluid will be overheated near the heater.

Bubble Pump

T.K. Jun and C.-K. kim, J. Appl. Phys., Vol. 83, No. 11, 1998

Magnetic Pump

Magnetic Pump-example

Ultrasonic pump

Acoustic pump-example

Pump by interfacial tension

Interfacial tension pump- Example