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Lumped
Electromechanical Elements
applied voltages, the material properties (polarization), and the geometry.
Thus, because (2.1.27) is an integral over space, the charge q is a function of
the applied voltages, material properties, and geometry.
If we again consider the system in Fig. 2.1.6 and specify that the time
variation of the geometry is uniquely specified by a mechanical displacement
x with respect to a fixed reference, we can write the charge in the general
functional form
q
=
q(v,
x).
(2.1.29)
In writing the charge in this way we have indicated explicit functional
dependence on only those variables
(v
and x) that may be functions of time.
We can now use (2.1.29) in (2.1.28) to obtain the terminal current as
i
q dv
+
q dx
(2.1.30)
av dt
ax dt
The first term exists only when the voltage is changing with time and the
second term exists only when there is relative mechanical motion.
If we consider a system whose polarization density P is a linear function
of field quantities, the system is
electricallylinear
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This note was uploaded on 02/10/2012 for the course MECE 4371 taught by Professor Liu during the Fall '11 term at University of Houston.
 Fall '11
 Liu

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