The ultrasonic motor, invented in 1980, utilizes the piezoelectric effect in the ultrasonic frequency range to provide its motive force, resulting in a motor with unusually good low-speed, high-torque and power-to-weight characteristics. This introduction to the general theory of the ultrasonic motor was written by the motor's inventor and an expert in conventional electric motors. It details many of the motor's applications, including those in camera autofocus mechanisms, medical equipment subject to high magnetic fields, and motorized car accessories. Electrical and electronic research engineers as well as students will find this an invaluable introduction to this important new invention.