The
piezoelectric effect for a given item depends on the type of
piezoelectric material and the mechanical and electrical axes of
operation can be precisely orientated within the shape of the
ceramic. These axes are set during "poling"; the process
that induces piezoelectric properties in the ceramic. The
orientation of the dc poling field determines the orientation of
the mechanical and electrical axes.
The poling
field can be applied so the ceramic exhibits piezoelectric
responses in various directions or combination of directions.
The poling
process permanently changes the dimensions of a ceramic element.
The dimension between the poling electrodes increases and the
dimensions parallel to the electrodes decrease. The effect is
shown in the fig 1, albeit greatly exaggerated.
Axes
Piezoelectric materials are anisotropic - their electrical,
mechanical, and electromechanical properties differ for electrical
or mechanical excitation along different directions. Thus for
systematic tabulation of properties, we require a standardized
means for identifying directions. Where crystals are concerned, we
use the orthogonal axes originally assigned by crystallographers.
However, we identify the axes by numerals:
1 corresponds to x axis,
2 corresponds to y axis,
3 corresponds to z axis.
Piezoelectric
ceramics are isotropic and are not piezoelectric before poling.
Once they are polarized, however, they become anisotropic. The
direction of the poling field is identified as the 3 direction. In
the plane perpendicular to the 3 axis, the ceramics are non
directional. Accordingly, the 1 and 2 axes may be arbitrarily
located but, of course, they must be perpendicular to each other.
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.
