Integration and wireless control methods for micromachined shape-memory-alloy actuators and their MEMS applications


Bulk-shape memory alloy actuators have great potential to be used in various microdevices. Previous studies show that this material is very attractive due to its very large force, high mechanical robustness with a simple structure and biocompatibility. These properties have resulted in its commercialization for various applications including those in biomedical field. Yet their advantages have not been fully utilized. For example, the commonly used actuation mechanism using Joule heating which requires wired interfaces limits their application especially in those instances where access and space are very limited. In addition, their incompatibility with the standard MEMS fabrication process further limits their potential for use in microscale devices. This thesis presents a novel technique for the wireless control of shape-memory alloy microactuators and the method for integrating bulk-micromachined shape memory alloy material into the MEMS fabrication process. The wireless control of shape memory alloy actuators using radiofrequency magnetic field wireless heating through resonant planar coils to directly drive the actuator without the use of conditioning circuits is demonstrated. An electroplating bonding technique is developed to integrate the bulk-micromachined shapememory alloy to the planar heater and the bonding strength is evaluated. A shape-memory alloy microgripper is fabricated and reported using developed actuation and the integration technique. Multiple actuator control is demonstrated using frequency modulated signals and its application in a form a microsyringe employing three actuators is reported. To improve the temporal response of the actuator, the wireless resonant heater circuit is fabricated using a shape-memory alloy to form an out-of-plane spiral coil which acts as the receiver coil as well as the actuator. Wireless displacement control and monitoring is also demonstrated using the fabricated device. The presented radiofrequency wireless control method also provides a platform to investigate the wireless actuation of the thermal based actuators other than the shape-memory alloy. The reported integration method also provides a means to exploit bulk materials into the MEMS fabrication process.

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