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Microvalves are a
key
component
for fluid flow
control in many microfluidic systems; e.g. chemical
microanalyser or drug delivery system. These valves can be
fabricated as stand alone devices in
flow
channels or
integrated with other microfluidic components, such as
micropumps or micromechanical sensors. The microvalves
developed to date can be classified in two categories; passive check valves and active valves driven with an
actuator.
Passive valves (without actuators) are mainly used as check
valve components in micropump and microfluidic systems. In
micropump applications, the integrated valves minimise leakage
under reverse pressure and have a high forward to reverse flow
ratio. These valves can be fabricated by bulk etching of
silicon,
mirolamination of thin metals
and
surface machining of polysilicon or polymer materials,
such as polyimide, parylene or silicone rubber.
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The
passive valve devices normally consist of either cantilever or
membrane on the silicon surface, which open and close to
enable and disable fluid flow during forward and reverse
pressures. The passive valve structure could also be
fabricated with non-moving parts, such as diffuser and nozzle
that operates to accelerate or decelerate a fluid flow by
changing its cross-sectional area along the flow axis. |
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Research
at
the NISRC
focused
on the development of two models of passive microvalves based
on silicon micromachining. Fluid flows through the valves is
in the opposite direction to each other and they are thus of
considerable potential in integrated microfluidic devices or
systems. In micropump applications, the valves form the inlet
and outlet components and can be fabricated on the same
surface with common process steps, removing the need for
precision processing on both wafer surfaces, hence enabling
further miniaturisation of the overall pump system. As
individual components, the valves offer quality sealing and
operate successfully with negligible reverse leakage. Fluid
flows through the valves are comparable to developed models,
and produce reverse flow rates as low as 0.5 % of the forward
flow.
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Click below for more details
of the individual microvalves;
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