1. Shawna Dean October 28, 2003 ENMA 490
The PDMS Membrane
Shawna Dean
October 28, 2003
ENMA 490

2. Outline Dimensions and pressures from previous work.
Group 1 (Quake)
Group 2 (Where we got our design from)
Deflection calculations for each group
Relating the calculated results with the experiment
Ending statement

3. Research Group 1: ‘Quake’
Typical membrane dimensions used where 100x100x10 micrometer active area for the valve.
Typically thickness: 30 micrometers
Applied pressure was in the order of 100kPa (1 atm)
*Young’s Modulus: 750 kPa
Still able to test with a ‘back pressure’ up to 70 kPa.
The valve could still close with the back pressure (remember the Quake design works with positive pressures) but had to add more pressure to the minimum closing pressure.

4. Research Group 2: Hosokawa *Origins of our valve design
Typical membrane area : 450x200x70 micrometers
Thickness used: 25 micrometers
Applied pressure: -30 to –40 kPa
Resulting pressure difference on the membrane is kPa.
Unfortunately this device could only optimally function with a positive internal pressure of 10 kPa or less.

5. Deflection of Known Designs
Using the information on the previous slides and the following equation:
Deflection =.00265P(ab)^2/ Et^3/(12*(1-v))
For Group 1 the deflection should be 3.37 micrometers
(for P=100kPa)
For Group 2 the deflection should be 110 micrometers
(for P=10kPa)

6. Does it make sense?
The deflection calculations for Group 1 seem to be on track. Even though they never quoted what the deflection was we know several hundred kPa’s will close the channel. Their channel depth is 10 micrometers. With 100kPa they are 1/3 closed. If the pressure is increased 3 times then the channel should be closed.
The deflection for Group 2 seems too high, being at 110 micrometers and the channel depth just 70 micrometers. But the paper admitted to having pressure problems, and may have been using too high a pressure.

7. Conclusions
Though both groups never quoted the deflection, they gave us enough information to see if we are on the correct path. I believe the equations are predicting values close to the experimental results, especially for Group 1.
As you increase the area of the membrane the pressure needed to deform it will decrease. Since our active area is so large, we may run into problems
Increase in thickness will help make the valve less sensitive. But thickness is also limited due to processing limits and dimensions of the control channel underneath.

8. References
“Monolithic Microfabricated Valves and Pumps by Multilayer Soft Lithography”. MA Unger, HP Chou, T Tohorsen, SR Quake. Science 288, pg113 (7 Apr 2000)
“A pneumatically-actuated three-way microvalve fabricated with polydimethylsiloxane using the membrane transfer technique”.
K Hosokawa and R Maeda. J.Micromech. Microeng. 10, pg415 (2000).