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Electronic Pressure Element - Piezoelectric |
The piezoelectric effect is a phenomena resulting from a coupling
between the electric and mechanical properties of a material. When
mechanical stress is applied to a piezoelectric material, an electric
potential will be produced. Likewise, when an electric potential is
applied to the material a mechanical change will occur. Piezoelectric
materials thus have numerous applications as electro-mechanical
transducers - devices which can convert electrical signals into
mechanical motion and vice-versa. Commercial applications of
piezoelectric devices abound, for instance in speakers, spark generators
inside electronic igniters, strain sensors pressure gages and as precise
time-keepers in electronic clocks. A few types of basic piezoelectric
devices include crystals, tubes, unimorphs, bimorphs and stacks.
Piezoelectric crystals involve a non-uniform charge distribution within
the unit cell of the crystal. When exposed to an electric field, this
charge distribution shifts and the crystal will change its shape. The
same polarization mechanism can cause a voltage to develop across the
crystal in response to mechanical force.
Piezo tubes are useful devices for fine control of an object in space.
By sectioning the surface of a tube into four regions and connecting
them, as well as one end of the tube to electrodes, it becomes possible
to apply voltages to the tube in various directions. By applying
voltages perpendicular to the tubes cross-section, it becomes possible
to control the position of one end of the tube in two dimensions (x and
y), while applying a voltage along the length of the tube, it becomes
possible to control the position in the third dimension (z).
Because the force and displacement created by a pure piezoelectric
material is relatively small, methods have been developed to allow
amplification of the piezoelectric effect. One approach (known as a
unimorph) is to apply a thin layer of a piezoelectric material to a
layer of inactive material. When the piezo expands or contracts, the
device will then bend in response.
By combining more than one piezo, it becomes possible to further
increase the amount of transduction. For instance, An elongating,
bending or twisting device can be created by placing two layers of
piezoelectric material on top of one-another, and by controlling the
polarization direction and the voltages such that when one layer
contracts, the other will expand. Such a device is known as a bimorph.
By stacking of piezo materials into layers, it becomes possible to
combine their displacement to create what is known as a piezo stack.
Such devices are capable of higher displacements and larger forces.
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