Together with an undergraduate project student, Samarth Bhargava, we investigated a novel type of ultrasonic motor, recently reported by James Friend and co-workers.This motor induces rotation of an object placed on the tip of a spiral that is ultrasonically actuated. The tip of the spiral undergoes rotation and extention and induces rotation in a manner very similar to that of a cook throwing a pizza. The photograph below shows a spiral plexiglas stator excited by piezoelectric wafers with a brass rotor. The brass rotor is painted so the rotational velocity can be measured.
Samarth Bhargava won first prize for his paper at the Innovative STEM Symposium in Baltimore in 2009. He subsequently presented a paper at the IEEE Ultrasonic Symposium which was accompanied by a related paper on simulations of motor operation.
An intriguing aspect of this motor is that the direction of rotation depends on the frequency of the excitation.
Animations showing the rotation in two different directions are linked below. (These are for a motor with different dimensions from the motor in the figure above).
Motor at 70000 Hz
Detail at 70000 Hz
Detail at 42500 Hz