After the
poling process is complete, a voltage lower than the poling
voltage changes the dimensions of the ceramic for as long as the
voltage is applied.
A voltage
with the same polarity as the poling voltage causes additional
expansion along the poling axis and contraction perpendicular to
the poling axis (fig. 2). A voltage with the opposite polarity has
the opposite effect: contraction along the poling axis, and
expansion perpendicular to the poling axis. In both cases, the
ceramic element returns to its poled dimensions when the voltage
is removed from the electrodes. These effects are shown greatly
exaggerated in fig. 2.
Piezoelectric
Voltage
After
the poling process is complete, compressive and tensile
forces applied to the ceramic element generate a voltage.
Refer to fig. 3. A voltage with the same polarity as the
poling voltage results from a compressive force (a) applied
parallel to the poling axis, or from a tensile force (b)
applied perpendicular to the poling axis. A voltage with the
opposite polarity results from a tensile force (c) applied
parallel to the poling axis, or from a compressive force (d)
applied perpendicular to the poling axis.
The instances above can also be arranged to occur in the
other two planes, i.e. thickness shear and face shear.
Generally
two or more of these actions are present simultaneously.
In some cases one type of expansion is accompanied by
another type of contraction which compensate each other
resulting in no change of volume. For example, the
expansion of length of a plate may be compensated by a n
equal contraction of width or thickness. In some
materials, however, the compensating effects are not of
equal magnitude and net volume change does occur. In all
cases, the deformations are very small when amplification
by mechanical resonance is not involved. The maximum
displacements are on the order of a few microinches.
Each
MEC Manufacturing Site has a Sales Department who will be pleased to
respond to your enquiries. In addition, the Morgan Technical
Ceramics Regional Sales Offices can provide you with local support.
