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Piezoelectric overview v2005

Piezoelectric overview v2005 - Background Definitions...

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Polarization is the amount of charge associated with the dipolar or free charge in a dielectric Pyroelectricity: when temperature increased, electric charges appear on the surface of the crystal (tourmaline the “Ceylon magnet,” 1703) Ferroelectrics: materials in which spontaneous polarization can be altered by electric field. Ferroelastics: materials in which mechanical stresses alter the spontaneous polarization. Piezoelectric: material in which application of stress generates electric charges on its surfaces; implies “direct piezoelectric effect” Electrostriction is a secondary coupling in which the strain is proportional to square of the electric field; frequently implies the “inverse piezoelectric effect.” Direct piezoelectric effect: convert mechanical energy into electrical (Pierre Currie in 1880) Inverse effect: convert electrical energy into mechanical (Lippman from thermodynamic principles; Currie experimentally in 1881)
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Electric field Dielectric displacement (flux) A q D = d V E = Electrostatic j ij i E D ε = Elastic kl ijkl ij S s σ = Constitutive equations ρ σ = = i i i j ij D f , , i i i j j i ij E u u s , , , ) ( 2 1 φ = + = Equilibrium Displacement s j ij jk ijk i k ijk kl E ijkl ij E s d D E d S s ε ε σ + = + = O Electro-mechanical coupling: stored mechanical energy input electrical energy stored electrical energy input mechanical energy = K 2 =
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