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Applications of Shape Memory Alloys to MEMS MAE 268
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Transcript of Applications of Shape Memory Alloys to MEMS MAE 268
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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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MicrogripperTheory 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