Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2001-12-19
2004-09-21
Budd, Mark (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S317000, C310S328000, C310S330000
Reexamination Certificate
active
06794795
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to piezoelectric devices, and more particularly to heating piezoelectric devices through an excitation signal.
BACKGROUND
Piezoelectric devices, such as piezoelectric actuators, generally consist of a piezoelectric material that deforms when an electric field, e.g., a driving field, is applied across it. Additional materials may be bonded with the piezoelectric material, such as metallic layers that act as electrodes, insulating materials to prevent current from flowing between particular areas of the device, and adhesives to bond the various layers together.
In simplified terms, piezoelectric materials are comprised of many dipole unit cells.
FIG. 1
symbolically depicts a unit cell
10
of a piezoelectric materia. When an electric field E
1
is applied in the direction shown, the unit cell grows in the y axis and shrinks in the x axis, in essence becoming tall and thin. Conversely, when an electric field E
2
is applied in the direction shown, the unit cell shrinks along the y axis and grows along the x axis, in essence, becoming short and fat.
As the unit cell
10
becomes colder, the piezoelectric effect, i.e., response to the application of an electric field, decreases. Thus, for a given magnitude of an electric field, the unit cell will not grow/shrink as much as it did when it was warmer. As a practical matter, for the same electric field applied, this decreases the stroke of the piezoelectric device. For example, for some piezoelectric materials, a 35% loss of stroke was found when the temperature changed from 25 degrees Celsius to −40 degrees Celsius.
SUMMARY OF THE INVENTION
The present invention provides apparatus and methods for exciting a piezoelectric device. A control device receives a first control signal excites the piezoelectric device at about at least one predetermined electrical resonant frequency of the piezoelectric device as a function of the first control signal.
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Budd Mark
Caterpillar Inc
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