piezoelectrics

Piezoelectricity is the coupling between mechanical and electrical states in certain materials. When subjected to mechanical stress, these materials generate an electric charge (the direct piezoelectric effect). Conversely, applying an electric field induces mechanical strain (the converse piezoelectric effect). The effect requires a crystal structure that lacks a center of symmetry and is strongest in certain ferroelectric materials. In practice, natural crystals such as quartz and Rochelle salt, as well as engineered ceramics and polymers, exhibit piezoelectric behavior to varying degrees.

Materials commonly used include natural quartz; Rochelle salt (historical); and synthetic ceramics such as lead zirconate titanate (PZT), barium titanate, and lead-free alternatives like potassium sodium niobate. Polymers such as polyvinylidene fluoride (PVDF) also display piezoelectricity with greater flexibility. The strength and behavior are described by piezoelectric coefficients (d, e, g), with d33 representing charge-induced strain along the polarization direction. Performance depends on temperature, frequency, domain structure, and aging of the material.

Applications are broad. In sensors, piezoelectrics serve as accelerometers and pressure sensors; in actuators, they provide precise micropositioning and valve control; in electronics, quartz crystal units stabilize oscillators for timing. Medical ultrasound uses high-power piezoelectric transducers to generate and receive acoustic waves. They are also used for energy harvesting from ambient vibrations and, in simple devices, as igniters in lighters.

History and development: piezoelectricity was discovered in 1880 by Jacques and Pierre Curie. The concept was extended to ferroelectric materials and, in the mid-20th century, to high-performance piezoelectric ceramics such as PZT, enabling widespread commercial devices and actuators.

Limitations include temperature sensitivity near phase transitions, aging and hysteresis, mechanical fatigue under cyclic loading, and environmental concerns related to lead-containing ceramics. Material choice and device design balance linearity, coupling efficiency, stability, and cost.