Microfluidics for Biologists Fundamentals and Applications

3.4 Micro-pump

Micro-pump are MEMS based fluid handling devices which again work passively
or actively to initiate flow through micro-channels. One of their critical purposes is
to initiate micro-flows of samples of fluids (either chemical or biochemical) for
reaction assays for diagnostics applications. The pump volume is generally of the
order of volume of the sample that is being transported. Micro-pumps can be of
mechanical or non-mechanical type depending on the actuation principle that they
may possess. In mechanical micro-pumps the actuation methods can be electro-
static, magnetic, piezoelectric, pneumatic and thermo-pneumatic etc. while in
non-mechanical systems actuation scheme like electro-osmotic, electro-hydrody-
namic, electrochemical or ultrasonic etc. can be deployed. It is generally observed
that the flow rates in case of mechanical micro-pumps are orders of magnitude more
than the non-mechanical micro-pumps.
The first ever peristaltic micro-pump was patented by Smits in 1989. This was a
silicon based device fabricated using already established MEMS fabrication tech-
nology, and was provided with a set of piezoelectric valves which would deflect and
squeeze out on chambers in a sequential manner. This pump had a maximum flow
rate of 3μL/min at zero back pressure and a Maximum Pressure head of 0.6 m
H 2 O. Further, it was observed that the discharge rate varied linearly with the back
pressure till a threshold frequency of 15 Hz was met beyond which it started to fall

2 mm 2 mm

16.15

mm

1.46 mm

Silicon oil filled micro -channels

Adhesive Layer

2 mm 2 mm

16.15mm

1.46 mm

1.46 mm

Adhesive Layer

Silicon oil filled micro

Aluminum Plate

Aluminum Plate Aluminum Plate

-channels

Loss Factor (

η)

0.35

0.30

0.25

0.20

0.15

0.10

0.05

0.00

-0.050 1 2 3 4 5 6 7

Number of Rows of Micro Channels

PDMS

Block

PDMS

Block

UnconstrainedConstrained

ab

c

Fig. 2.11 (a) Schematic of unconstrained mode damping. (b) Schematic of constrained mode
damping. (c) Loss factor plot with respect to number of rows of embedded channels in both
constrained and unconstrained damping analysis (Reproduced from Singh et al. [ 27 ] with permis-
sion from the Institute of Electrical and Electronics Engineers)

48 G. Bhatt et al.

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