Page 243 - Microsensors, MEMS and Smart Devices - Gardner Varadhan and Awadelkarim

APPLICATIONS 223

Table 7.2 Technical specification of microvalves
Valve part Value
Valve chamber size (mm) 5 x 5 x 1
Valve chamber material PMMA
Fluid chamber size (mm) Diameter 3, height 0.125
Actuator chamber size (mm) Diameter 3, height 0.125
Inlet opening diameter (um) 100
Membrane diameter (mm) 3
Membrane thickness (urn) 25
Membrane material Polyimide
Membrane deflection (um) 120 max.
Maximum flow rates and inlet 0.49 m//s at 740 hPa
pressure
Lifetime (load cycles) >285 million

350-
300-
250-
200-
150- Actuator pressures to close the valve
100-
50- Actuator pressures to open the valve
0- ^ - /^ - • •- *
-50
-100
0 100 200 300 400 500 600 700 700 800
Inlet pressure (hPa)
(a)

Figure 7.67 Characteristics of a microvalve fabricated by the AMANDA process: (a) actuation
pressure and (b) volumetric flow rate

data on these microvalve samples are listed in Table 7.2 and the measured characteristics
of the microvalve are presented in Figure 7.67. Applications include integral components
of pneumatic and hydraulic systems, systems for chemical analyses of liquids and gases,
dosage systems for medical applications, and so on.
AMANDA has also been used to fabricate transducers. For polymer membranes, the
low Young's modulus results in large deflections and strains at comparatively low pressure
loads. Therefore, polymer pressure transducers are suitable for measuring small differential
pressures. A schematic view of a pressure transducer is shown in Figure 7.68 (Martin
3
et al. 1998); the outer dimensions of this transducer are 5.5 x 4.3 x 1.2 mm . The thin
polyirnide diaphragm supports strain gauges made of gold, covered by a 30 um-thick
polyimide disk. This disk bends by the pressure dropped across the diaphragm, and the
generated strain is measured with a Wheatstone bridge.
A volume flow transducer based on pressure difference measurement is shown in
Figure 7.69 (Martin et al. 1998). The pressure drop along a capillary is measured and
the flow rate is then calculated. These transducers can be easily integrated into the
polymer micropump and microvalves developed by the AMANDA process to form a
fully integrated microfluidic system.