A piezoelectric motor is a device that creates motion when an electric field creates movement in certain crystals or man-made materials. Piezoelectricity was first demonstrated in the 1880s, when it was discovered that quartz crystals created electric currents when stressed by hitting or compressing them. This effect is the opposite of what powers a piezoelectric motor, where the electricity is used to create movement from a material sensitive to the electric field.
The need for these motors grew in the late 20th century with increasing demand for miniaturization. Standard electric motors have a minimum-size practical limit, below which they cannot operate reliably. A piezoelectric motor can be made in miniature scale, provides precise movement in very small increments, and uses very little power during operation or while at rest.
There are very few parts in a piezo motor. A high-frequency oscillator provides a frequency that excites the piezoelectric material. This material will change shape based on its crystal properties. The resulting movement causes the material to come into contact with a slide or roller.
The slide or roller is coated with a soft rubber or polymer, called a friction coat, which permits the piezoelectric material to grip and move it. Each time the oscillator creates a frequency pulse the material is excited and moves. This causes movement of the slide or roller.
A piezoelectric motor makes use of this effect by rapidly turning the oscillating frequency on and off. Each pulse creates a small but well-defined movement of the piezo material, and the rapid frequency cycles create a continuing movement. Slides can replace rotors for a back-and-forth movement that can act as a switch.
The greatest advantage of these motors has been miniaturization. There are other advantages as well, including low power requirements and little need for maintenance. A piezoelectric motor is also relatively unaffected by magnetic and electrical interference, because the crystal structure requires specific frequencies to create movement.
Natural crystals including quartz and tourmaline can provide piezoelectric properties. Ceramics based on titanium and other minerals are commonly used. Some polymers based on fluoropolymer technology can exhibit piezoelectric properties as well.
A standard electric motor can provide high speed with low torque, the twisting force that causes rotation. Piezo motors, on the other hand, operate at lower speeds but have high torque for their size. In addition, they can provide very precise movements not possible with electric motors. The ability to miniaturize to nanoscale, or microscopic size, allows them to be used in a wide variety of medical, industrial and consumer applications.