Mechanism Piezoelectric plate used to convert audio signal to sound waves The nature of the piezoelectric effect is closely related to the occurrence of electric dipole moments in solids. The latter may either be induced for ions on crystal lattice sites with asymmetric charge surroundings (as in BaTiO 3 and PZTs)or may directly be carried by molecular groups (as incane sugar). The dipole density orpolarization (dimensionality [Cm/m 3 ] ) may easily be calculated for crystals by summing up the dipole moments per volume of the crystallographic unit cell. [11] As every dipole is a vector, the dipole density Pis avector field.Dipoles near each other tend to be aligned in regions called Weiss domains. The domains are usually randomly oriented, but can be aligned using the process of poling (not the same as magnetic poling) , a process by which a strong electric field is applied across the material, usually at elevated temperatures. Not all piezoelectric materials can b e poled . [12] Of decisive importance for the piezoelectric effect is the change of polarization Pwhen applying amechanical stress.This might either be caused by a re-configuration of the dipole- inducing surrounding or by re-orientation of molecular dipole moments under the influence of the external stress. Piezoelectricity may then manifest in a variation of the polarization strength, its direction or both, with the details depending on 1. the orientation of Pwithin the crystal, 2. crystal symmetry and 3. the applied mechanical stress. The change in Pappears as a variation of surfacecharge density upon the crystal faces, i.e. as a variation of the electrical field extending between the faces caused b y a change in dipole d ensity in the bulk. For example, a 1 cm 3 cube of quartz with 2 kN (500 lbf) of correctly applied force can produce a voltage of 12500 V. [13] Piezoelectric materials also show the opposite effect, called converse piezoelectric effect, where the application of an electrical field creates mechanical deformation in the crystal.
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Piezoelectric plate used to convert audio signal to sound waves
The nature of the piezoelectric effect is closely related to the occurrence of electric dipole
moments in solids. The latter may either be induced for ions on crystal lattice sites with
asymmetric charge surroundings (as in BaTiO 3 and PZTs) or may directly be carried by
molecular groups (as in cane sugar) . The dipole density or polarization (dimensionality [Cm/m 3]
) may easily be calculated for crystals by summing up the dipole moments per volume of the
crystallographic unit cell .[11] As every dipole is a vector, the dipole density P is a vector field.
Dipoles near each other tend to be aligned in regions called Weiss domains. The domains are
usually randomly oriented, but can be aligned using the process of poling (not the same as
magnetic poling) , a process by which a strong electric field is applied across the material, usually
at elevated temperatures. Not all piezoelectric materials can be poled .[12]
Of decisive importance for the piezoelectric effect is the change of polarization P whenapplying a mechanical stress. This might either be caused by a re-configuration of the dipole-
inducing surrounding or by re-orientation of molecular dipole moments under the influence of
the external stress. Piezoelectricity may then manifest in a variation of the polarization strength,
its direction or both, with the details depending on 1. the orientation of P within the crystal, 2.
crystal symmetry and 3. the applied mechanical stress. The change in P appears as a variation of
surface charge density upon the crystal faces, i.e. as a variation of the electrical field extending
between the faces caused by a change in dipole density in the bulk. For example, a 1 cm 3 cube of
quartz with 2 kN (500 lbf) of correctly applied force can produce a voltage of 12500 V.[13]
Piezoelectric materials also show the opposite effect, called converse piezoelectric
effect , where the application of an electrical field creates mechanical deformation in the crystal.
Piezoelectricity is the combined effect of the electrical behavior of the material:
Where D is the electric charge density displacement (electric displacement ), ε is permittivity and
E is electric field strength, and Hooke's Law:
Where S is strain, s is compliance and T is stress.
These may be combined into so-called coupled equations, of which the strain-charge form is:
In matrix form,
Where the matrix for the direct is piezoelectric effect and is the matrix for the converse
piezoelectric effect. The superscript E indicates a zero, or constant, electric field; the superscript
T indicates a zero, or constant, stress field; and the superscript t stands for transposition of a
matrix.
The strain-charge for a material of the 4mm (C4v) crystal class (such as a poled piezoelectric ceramic such as tetragonal PZT or BaTiO 3) as well as the 6mm crystal class may