Modeling, Fabrication and Testing of PZT Based MEMS and Meso-scale Pneumatic Proportional Valves
2019-12
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Modeling, Fabrication and Testing of PZT Based MEMS and Meso-scale Pneumatic Proportional Valves
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2019-12
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This thesis presents new modeling and process techniques used for the design and fabrication of Micro-Electro-Mechanical Systems (MEMS) based proportional valves for pneumatics applications. The modeling approach is further applied to a similar but larger envelope valve, hence called meso-scale valve, used to demonstrate the concept of the MEMS valve. Since the meso-scale valve is entirely fabricated in the machine shop using conventional machining technology and off-the-shelf components, the fabrication technique presented in the thesis applies to the MEMS valve only. The modeling work consists of two main sections: actuator modeling and flow modeling. In the actuator modeling section, a closed-form deflection equation of a piezoelectric bimorph is derived. The model takes into account the effect of the adhesive and electrode layers. The deflection model is used in a comprehensive steady state force model of a piezoelectric bimorph. In the flow modeling section, flow through the meso-scale and MEMS valves is modeled as an axisymmetric frictional flow between parallel plates. Friction factor is allowed to vary as a function of the Reynolds number in a new piecewise function for different regimes of the flow. The new flow modeling technique can be used estimate flow through the valve based on the position of the valve actuator. Without fabrication considerations, the actuator and flow modeling techniques are used to show that target specifications of 2cm3 MEMS valve with 700 kPa maximum pressure differential and 25 slpm flow capacity can be met. The success of such new MEMS valves has a revolutionary potential to miniature valve technology. The modeling techniques are used to design the final MEMS valve that was fabricated in the clean-room. The MEMS valve is created in a unique method that involves three separate processes: port plate fabrication, actuator fabrication, and bonding. In the port plate fabrication, the orifice array is created on standard silicon substrates using dry etching techniques. High aspect ratio (up to 20) through holes are created on standard silicon wafers using the technique. The actuator fabrication is performed on a separate substrate with bulk micromachining being the general fabrication methodology. Unique etch techniques have been used to release the actuator array. In the bonding process, adhesive bonding is used to permanently bond the port plate and the plate carrying the actuator array. The testing section presents testing of the port plates and actuators separately before testing the valves as complete sets. The port plate test results have demonstrated that target pressure and flow specifications of the MEMS valve are met. The actuator array tests have also shown that functional actuator arrays with deflection values that are nearly 90% of the predicted deflection have been successfully fabricated. The mesoscale valve test has produced results with proportional relationship between voltage and actuator deflection for a good range of the applied voltage. Several of the MEMS valves tested suffered from electrical shorting while in the test stand. However, one of the valves has shown promising results where flow rate increases with increases in applied voltage were recorded.
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University of Minnesota Ph.D. dissertation. December 2019. Major: Mechanical Engineering. Advisor: Thomas Chase. 1 computer file (PDF); xiv, 246 pages.
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Fikru, Nebiyu. (2019). Modeling, Fabrication and Testing of PZT Based MEMS and Meso-scale Pneumatic Proportional Valves. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/211751.
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