Ph.D. Proposal Presentation by Jemmy Sutanto Bintoro
Monday, September 29, 2003
(Dr. Peter Hesketh, advisor)
"A Bistable Electromagnetic Actuated Microvalve"
This proposal presents a design and fabrication for a bistable electromagnetic actuated microvalve. The function of the valve is to control the fuel delivery system in a fuel cell unit for power generation. The complete magnetically close structure has been designed by using ANSYS 5.7. The valve actuator consists of three main parts, an electromagnetic coil, a support structure, and a membrane. The bistable concept of the electromagnetic valve is achieved by implementing permanent magnet attached either on the back of the wafer or being electroplated on the bottom of the membrane.
The microvalves are fabricated on top of a single wafer that uses 8 masks steps. The fabrication processes were entirely done by surface micromachining and electroplating on a single wafer with the maximum fabrication temperature of 300 ºC, providing potentially a CMOS compatible process. For the inlet fluidic connection, a hole is etched through the back of wafer after the valve structure been built on the top of wafer.
The experimental data on the membrane stiffness shows good agreement with the predicted ANSYS 5.7, of the value the force requires to fully deflect the membrane at a distance of 12 µm. The membrane deflects rapidly in the order of ms in the air at drive frequency of 100 Hz is applied, that corresponds to energy of 6.96 mJ per actuation. The valve packaging for fluidic testing was developed by a mould made from a stereo lithography process. The mold is filled with PDMS to define the inlet and outlet fluidic channels for experimental tests, as well as providing sealing to the valve. The tests show that the pressure drop across the valve with an inlet diameter of 60 µm is in the order of 600 Pa for 1 µl/min fuel flow rate. This value is negligible compared to the expected 10 kPa pressure drop across the fuel cell channel. The addition of a parylene coating to the microvalve structure with the thickness 0.5 – 1 µm, improved the sealing performance of the valve in minimizing leakage.