The maximum depoling field a piece can withstand without experiencing depolarization is its coercive field, E c. The electrical response to mechanical stimulation is called the direct piezoelectric. In linear piezoelectric theory, the stress T or the electric displacement D of a piezoelectric material subjected to a field E or a strain S excitation is. This piezoelectric effect only occurs in non-conductive materials, such as quarts (SiO 2. The effect is reversible, so an electrical charge will cause the material to change shape. An applied electrical field produces a linearly proportional strain in these materials. Piezoelectric materials generate an electric charge across its surface when it undergoes mechanical stress, due to the asymmetry of its crystalline structure. Or, the electric dipoles may be partially or completely flipped around 180°, causing the piece to be repoled in the opposite direction. Piezoelectricity is the property of some materials to develop electric charge on their surface when mechanical stress is exerted on them. If too large a voltage is applied in the depoling direction, the original polarization will be degraded (partially or fully depolarized). These distortions are illustrated in Figure 2 for a rectangularly shaped piece. Again, it reverts to its original poled dimensions after removing the voltage. When voltage is applied opposite to the poled direction ( depoling direction), the piece contracts along the polar axis and expands in the transverse direction.
When the voltage is removed, the piece reverts to its original pole dimensions. When voltage is subsequently applied to the poled material in the same direction as the poling voltage, the piece experiences further elongation along the polar axis and transverse contraction as stipulated by Poisson’s ratio.
1 of this article, for example, 3 is the axis of poling (z or thickness. It is therefore important to have a form of notation that distinguishes clearly which axis is being referred to in any statement regarding a piezoelectric material.
During electrical polarization, the material elongates permanently in the direction of the poling field (polar axis) and contracts in the transverse direction. Piezoelectric materials are anisotropic that is, they do not have the same properties in all axes.
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