November 2000
Intermediate to advanced
608 pages
16h 12m
English
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6.2 PIEZOELECTRIC SENSORS
6.2.1 The Piezoelectric Effect
The piezoelectric effect is the appearance of an electric polarization in a material that strains under stress. It is a reversible effect. Therefore, when applying an electric voltage between two sides of a piezoelectric material, it strains. Both effects were discovered by Jacques and Pierre Curie in 1880–1881.
Piezoelectricity must not be confused with ferroelectricity, which is the property of having a spontaneous or induced electric dipole moment. Ferroelectricity was first discovered by J. Valasek in 1921 in Rochelle salt. All ferroelectric materials are piezoelectric, but the converse is not always true. Piezoelectricity is related to the crystalline (ionic) structure. Ferromagnetism is instead related to electron spin.
Piezoelectric equations describe the relationship between electric and mechanical quantities in a piezoelectric material. In Figure 6.14a, where two metal plates have been placed to form a capacitor, for a dielectric nonpiezoelectric material we have that an applied force F yields a strain S that, according to Hooke’s law (Section 2.2), in the elastic range is
where s is compliance, 1/s is Young’s modulus, and T is the stress (F/A).
A potential difference applied between plates creates an electric field E and we have where D is the displacement vector (or electric flux density), is the dielectric ...
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