What is an ultrasonic motor?

Basically, an USM (Ultrasonic motor) consists of a rotor, a stator, and piezoelectric ceramics.
Here, Piezoceramics can produce electricity when subjected to mechanical stress like a hit, twist, pressure, it called Piezoelectric effect. On the contrary, when the electricity is given to piezoceramics, it can be contracted or expanded to certain direction. this is inverse piezoelectric effect. USMs use this effect.
USM is based on ultrasonic vibrations of the stator, obtained by piezoceramics. Another component, the rotor can be moved by this vibration.
Why uses USM? because it has the following advantages:
high resolution, quick response, low power consumtion, no break mechanism, small size and weight, no electromechanical noise, and so on.
Today, I'd like to briefly introduce a rotary typed ultrasonc motor.

Left figure shows the structure of the rotary typed USM produced by Piezo technology in Korea. Many pieces of piezoceramics attached to the stator (white color), and the rotor and stator combine with pressure of the spring. when the stator generates vibrations such as a travelling wave, the rotor can be moved by friction between the stator.
below shows the simulation of rotary typed USM and movie of panasonic usm to help you understand better.  I'm currently developing MRI-guided prostate surgical robot with this typed USM.