Optimization Of A Non-Contact Single Phase Drive Ultrasonic Micromotor: Via Design And Analysis Of Engineered Stator Curvature And Surface Acoustic Streaming Actuators
We present new design methodologies of the Whispering Gallery Mode Micro Ultrasonic Motor (WGMMUM) that enable control of motor rotation direction, and enable controlled levitation of the rotor. These design degrees of freedom provide insights into future optimization of the motor for high torque density output, allowing for long-term air-operation, low voltage and power consumption, leading to CMOSelectronics compatible ultrasonic micromotors. The MUMPS/PZT motor operates with a drive voltage of 4 - 10 Vpp in the frequency range of 100 kHz - 5 MHz, creating rotation through frictional coupling and acoustic streaming in the rotor-stator gap. Using interferometer measurements, we demonstrate smooth rotation of micromotor at 100 - 500 rpm. We implemented multiple gear coupled surface micromachined ultrasonic motors to achieve direction control, providing frequency selective motor operation. The ultrasonic motor utilizes radial and circumferential periodic variation of stator curvature that periodically modulates the gap between the rotor and the stator. We demonstrated designs of the stator with periodic patterns of gold layer as a method to induced theta periodic gaps between the stator and the rotor. The analytical analysis of the multilayer structure matched well with the measured curvature information. The motor is designed to be tested under optical interferometer at different operating temperatures. Temperature dependence of the curvature demonstrates that temperature can be used to control the efficiency and coupling of the ultrasonic motor. A thermal actuator driven gripper actuator is used as a braking mechanism, but experimentally seen to control not only the speed but also the direction of the rotor motion by modulating the rotor gripper gap in nanometer dimensions. Analysis and experiments show the operating mechanism as acoustic streaming forces in the air gap between the gripper and the rotor, providing an active MEMS approach to generate acoustic streaming actuators. Upon preliminary demonstrations of levitation of the motor, non-contact control of angular speed, and non-contact optical means of measurement, towards the use of ultrasonic micromotor as a rotation platform for inertial sensor calibration, we fabricated a gyroscope and showed a method of attaching a separate chip to a released motor using a focused ion beam nano-welding process.
micromotor; PZT; thermal actuator
Zehnder, Alan Taylor; Bhave, Sunil A.; Molnar, Alyosha Christopher
Ph.D. of Electrical Engineering
Doctor of Philosophy
dissertation or thesis