Explain the Piezo Electric Theory, how it can be used to power pumps,
and where I can access information about pumps that are utilizing the
piezo electric theory.

Hello stom,
 here is the 101 of these materials

Piezoelectric effect is property of some materials to
 change their density in the electric field. Crystals,
 quartz for example, and some ceramics  have this property.
 Here is figure and bit of history:
http://members.tripod.com/~albert51/maz.html

 Dpending on how the piece is cut, and where the
 field is applied, one can get different deformations:
http://www.dbanks.demon.co.uk/ueng/pztact.html

 These effects (there is a whole family of them,
thermoelecttric, photoelastic, ..) are symetric,
 meaning: if  you bend the piezoelectric plate,
 (PZT) it will create voltage. (This is used in some
lighters:  the voltage is quiet high and may
produce a spark):

The molecular mechanism is a bit similar to 
permanent magnets. The molecules have to be
a aligned so that the effect is not canceled:
http://www.aurelienr.com/electronique/piezo/piezo.pdf

There is no particular theory here. People study 
different materials since the effect has many applications
and that research would come under 'statistical mechanics'
and 'irreversible thermodynamics', sometimes rheology.

Example of such a research is here:
http://electroceramics.mit.edu/actuators.html

Some theory and sample circuits is shown here:
http://www.globalspec.com/kistler/ref/tech_theory_text.htm

It is used for sensors, to drive ink-jets, and in quartz clocks,
and older radios a as frequency standard (since the natural resonance
of a crystal
can be excited by an electric circuit.).

 It can be used to build tiny electric motors.
They are smaller then conventional ones,  since they do not use
 magnetic field and do not need coils:
http://www.heason.com/support/piezo_electric_ceramic/downloads/Motor%20Implementations.pdf

That should cover the basics, but feel free to ask for specifics and
indicate if you
want more simple or more technical answer.

hedgie

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Clarification of Answer by hedgie-ga on 12 Jul 2002 15:19 PDT

For pumps in particular, try this search term in google: piezoelectric
pump

quite a few designs have peen posted:
www.control.hut.fi/Research/dms
www.islandone.org/.../ISDC99-Abstracts_CD/AIAA%20Abstracts/
Piezoelectric%20Pump%20Development.pdf
www.ptm.umn.edu/LT/LT_DETAIL_94102.pdf

  The typical  basic idea is simple:  PZT cystal is made to  excite
vibrations in the fluid
(this are usually ultrasound) and then a  'fuidic diode' acts as a
rectifier, converting
the AC flow to a DC stream.

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Clarification of Answer by hedgie-ga on 12 Jul 2002 15:37 PDT

Just one more link, and only since you used the word 'theory' .
The theory is not specific this effect (the link which follows gives
you a  list  of cross-effects).
and is part 'Irreversible Thermodynamics' .  I found this one,
freshman college level
textbook on the web:
http://www.iucr.org/iucr-top/comm/cteach/pamphlets/18/node3.html

One abstract and  nice theoretical result  known as Curie's Principle 
is
described here (same textbook)
http://www.iucr.org/iucr-top/comm/cteach/pamphlets/18/node8.html#SECTION00080000000000000000
lThe priciple limits the number of cross-effects which are allowed.
and is an example
of the symmetry based reasoning in physics.