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Applications of Shape Memory Alloys to MEMS MAE 268 Greg Jarmer and Garrett Uyema
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Outline of Presentation Shape Memory Alloys (SMA) Advantages of SMA’s for actuation of MEMS Devices Example of an Application: Microgripper Recommended Improvements of Microgripper Future Applications of SMA in MEMS
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Shape Memory Alloys Principles of Shape Memory Alloys –Shape Memory Alloys (SMA) are alloys that exhibit the shape memory effect. –The shape memory effect is the process of restoring a deformed material back to an initial shape through a thermally induced crystalline transformation –The crystalline transformation occurs between a low temperature ductile martensitic phase and a high temperature high strength austenitic phase.
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Shape Memory Alloys
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Advantages of SMA’s in MEMS The main advantages of SMA’s for micro- actuation are: –SMA’s are capable of producing a large actuation force –SMA’s are capable of producing large displacements –SMA’s are activated through thermal heating
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Disadvantages of SMA’s in MEMS The main disadvantages of SMA’s are: –Sensitivity of material properties in fabrication –Residual Stress’s developed in thin films –Nonlinearity of actuation force –Lower maximum frequency compared to other microactuator devices
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Verification of Activation Force with FEA
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Microgripper Theory of Operation 2 Main designs of microgrippers Location of TiNi thin film SMA actuation Transformation from martensite to austenite heating SMA thin film on the inside
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Microgripper Fabrication of the Microgripper –2 identical cantilevers and a silicon spacer –Processes used: Deposit and etch Thin film sputtering Annealing Eutectic bonding
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Recommended Improvements of Microgripper Be able to control hysteresis temperature range –Change composition of SMA Can shift hysteresis curve left or right –Alloy TiNi with another element such as Cu
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Recommended Improvements of Microgripper Reduce residual stress in the thin film –Need to reduce thermal mismatch between NiTi and Si substrate –Add a layer of tungsten (W) Difference in the coefficients of thermal expansion is reduced
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Recommended Improvements of Microgripper Increase the maximum frequency –Decrease the time it takes for phase transformation to occur –Increase surface area to volume ratio Heat can be dissipated faster
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Future Applications of Microgrippers Grab tiny foreign objects for removal from the body –Facilitates access to intricate regions of the body Microassembly for MEMS devices Intravascular Therapy
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Future Applications of SMA in MEMS MEMS and bioMEMS applications –Eliminate vibrations of read/write heads in hard disk drives –Microstents Promote flow in tubular passages Reinforce weak blood vessels –Microsurgery Cardiovascular applications Orthopedic applications
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Future Applications of SMA in MEMS Simon filter Microstents SMA basket Microwrapper
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