Piezoelectric materials belong to the so-called smart materials, or multi-
functional materials, which have the ability to respond significantly to
stimuli of different physical natures. Figure 4.1 lists various effects that
are observed in materials in response to various inputs: mechanical, elec-
trical, magnetic, thermal, light. The coupling between the physical fields
of different types is expressed by the non-diagonal cells in the figure; if
its magnitude is sufficient, the coupling can be used to build discrete or
distributed transducers of various types, which can be used as sensors, ac-
tuators, or even integrated in structures with various degrees of tailoring
and complexity (e.g. as fibers), to make them controllable or responsive
to their environment (e.g. for shape morphing, precision shape control,
damage detection, dynamic response alleviation,...).
MechatronicsDynamics of Electromechanical and Piezoelectric Systems, by
A. PREUMONTULB Active Structures Laboratory, Brussels, Belgium, page 95
Piezoelectric materials:(old description)
Piezo derives from the Greek verb piezin- "to press"- and piezoelectricity is a seperation of charge that occurs when pressure is applied to a piezoelectric material. The piezoelectric effect occurs only in certain crystalline electrical insulators, and the charge seperation is manifested by an electrical potential difference between opposite faces of a crystal. A converse effect to piezoelectricity also exists; when an electrical field is applied to a piezoelectric crystal, the crystal becomes distorted as long as the field is present.
Most piezoelectric materials are ionic salts, which consists of positively charged cations and negatively charged anions. In the solid state, these ions form a regular lattice that is described by a unit cell-the smallest group of ions that represent the whole structure of the cell- and a crystal can be thought of as a three-dimensional array of unit cells. A few piezoelectric materials are highly polar crystalline polymers, such as polyvinylidene chloride.
(Marshall Cavendish Corporation, How it works: science and technology, 2002, p. 1744)
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