Electrostriction

Electrostriction is a property of all electrical non-conductors, or dielectrics, that causes them to change their shape under the application of an electric field. (Compare with magnetostriction.)

Explanation

Electrostriction is a property of all dielectric materials, and is caused by the presence of randomly-aligned electrical domains within the material. When an electric field is applied to the dielectric, the opposite sides of the domains become differently charged and attract each other, reducing material thickness in the direction of the applied field (and increasing thickness in the orthogonal directions due to Poisson's ratio). The resulting strain (ratio of deformation to the original dimension) is proportional to the square of the polarization. Reversal of the electric field does not reverse the direction of the deformation.

More formally, the electrostriction coefficient is a fourth order tensor ($Q\_\{ijlk\}$), relating second order strain ($x\_\{ij\}$) and first order polarization tensors ($P\_k$, $P\_l$).

$x\_\{ij\}\; =\; Q\_\{ijkl\}\; imes\; P\_k\; imes\; P\_l$

It should be noted that the related piezoelectric effect occurs only in a particular class of dielectrics. Electrostriction applies to all crystal symmetries, while the piezoelectric effect only applies to the 20 piezoelectric point groups. Electrostriction is a quadratic effect, unlike piezoelecticity, which is a linear effect. In addition, unlike piezoelectricity, electrostriction cannot be reversed: deformation will not induce an electric field.

Materials

Although all dielectrics exhibit some electrostriction, certain engineered ceramics, known as relaxor ferroelectrics, have extraordinarily high electrostrictive constants. The most commonly used are:
* Lead magnesium niobate (PMN)
* Lead magnesium niobate-lead titanate (PMN-PT)
* Lead lanthanum zirconate titanate (PLZT)

Magnitude of effect

Electrostriction can produce a strain of 0.1 % at a field strength of 2 million volts per meter (2 MV/m) for the material called PMN-15 (TRS website listed in the references below). The effect appears to be quadratic at low field strengths (up to 0.3 MV/m) and roughly linear after that, up to a maximum field strength of 4 MV/m . Therefore, devices made of such materials are normally operated around a bias voltage in order to behave nearly linearly. This will probably cause deformations to lead to a change of electric charge, but this is unconfirmed.

Applications

* Sonar projectors for submarines and surface vessels
* Actuators for small displacements

See also

* Magnetostriction
* Piezoelectricity

References

* [http://www.britannica.com/eb/article-9032346 "Electrostriction." Encyclopædia Britannica. 2006. Encyclopædia Britannica Premium Service. 19 July 2006]
* "Mini dictionary of physics" (1988) Oxford University Press
* [http://www.trstechnologies.com/Materials/electrostrictive_materials.php "Electrostrictive Materials"] from TRS Technologies
* [http://www.tf.uni-kiel.de/matwis/amat/elmat_en/kap_3/backbone/r3_6_1.html#_dum_3 "Electronic Materials"] by Prof. Dr. Helmut Föll

External links