Piezoelectricity

Piezoelectricity, reversible relationship between mechanical stress and electrostatic potential exhibited by certain crystals with no center of symmetry, discovered in 1880. When pressure is applied to a piezoelectric crystal, such as quartz, positive and negative electric charges appear on opposite crystal faces. Replacing the pressure by tension changes the sign of the charges. If an electric potential is applied across the crystal, its length changes. A piezoelectric crystal placed in an alternating electric circuit will alternately expand and contract. Resonance occurs in the circuit when its frequency matches the natural vibration frequency of the crystal. This way of coupling electrical and mechanical effects is used in microphones, phonograph pickups, and ultrasonic generators.

See also: Quartz.