MIT Department of Electrical Engineering & Computer Science

SPECIAL EECS SEMINAR

Tuesday, April 18, 1995
Grier Room B, 34-401B

Refreshments at 3:45 PM
Talk at 4:00 PM

Piezoelectric Ultrasonic Micromotors

Anita M. Flynn
Massachusetts Institute of Technology

Utilizing the large piezoelectric coefficients and high dielectric constants of ferroelectric thin films, it is possible to microfabaricate ultrasonic motors on silicon substrates. This talk will describe our efforts in this area. By using ferroelectric thin films of lead zirconate titanate (PZT) a two-order of magnitude improvement over bvlk ceramic materials is obtained in breakdown strength. This characteristic, in combination with high dielectric permittivities, leads to a three-order of magnitude improvement over electrostatic micromotors in terms of energy densities.

We have fabricated resonant structures on one micron thick silicon nitride membranes which are able to spin two-millimeter diameter rotors which are placed down on top. Stator-rotor interaction is achieved through frictional coupling and an inherent geardown creates motors which run at low speeds with high torque. Models of line contact, Hertzian contact, and linear spring contact for Coulomb and viscous friction have been derived and simulations will be presented which predict speed-torque curves, efficiencies and overall output power for various conditions of operating voltage and normal force. A set of 8 mm diameter motors have been fabricated from bulk PZT to test these models.

We plan to incorporate these actuators into small robots and create truly integrated intelligent machines. Presently, we are developing small palm-sized autonomous robots, using conventional electromagnetic motors, which cna crawl through tubes, pick up small objects and cooperate on tasks. Videotapes will be shown of both the motors and these machines acting as a robotic ant colongy and as intestine crawlers for telepresence surgey.