Piezoelectric materials within a vacuum


by jf2086
Tags: piezo, vacuum, voltage
jf2086
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#1
Aug27-13, 06:27 AM
P: 4
Would a piezoelectric crystal create a negative voltage if held within a vacuum? Perhaps it's my misunderstanding of the materials properties, but it seems that if there is zero net output within the "creation"(0) atmosphere, and any slight elastic deformation shows its self in the form of an output, then a decrease in the pressure in which the material was created would produce some minute negative voltage output.
Is there something I am overlooking?
Thank you for your consideration.
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jf2086
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#2
Aug27-13, 06:36 AM
P: 4
I guess an increase in the pressure would also be an applicable question.
UltrafastPED
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#3
Sep2-13, 03:03 AM
Thanks
P: 1,364
This is a research topic; e.g., see "Voltage response of piezoelectric PVDF films in vacuum and at elevated temperatures": http://iopscience.iop.org/0964-1726/21/8/085028

DrDu
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#4
Sep2-13, 07:01 AM
Sci Advisor
P: 3,380

Piezoelectric materials within a vacuum


There is a duality between pressure and volume on one hand and stress and strain on the other.
Piezoelectricity is due to stress, not pressure. Hence changing the pressure will not induce a piezoelectric voltage, at least as long as the material is stress-free.
AlexCdeP
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#5
Sep2-13, 10:36 AM
P: 34
But there would be stress in the crystal if it was under pressure no?
DrDu
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#6
Sep2-13, 03:16 PM
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P: 3,380
Pressure, by definition, is the isotropic part of the stress tensor. If the crystal is homogeneous, there is no reason why pressure should go in hand with a non-isotropic stress.
jf2086
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#7
Sep3-13, 05:42 AM
P: 4
Thanks for your responses, gentlemen. Back to the drawing board!
UltrafastPED
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#8
Sep3-13, 05:54 AM
Thanks
P: 1,364
If a piezo only detects stress, and not pressure - then how can they make piezo absolute pressure gauges?

For example: http://www.mksinst.com/docs/UR/hps902ds.pdf

In answer to my own question: they only expose a portion of the piezo crystal.
See http://cds.cern.ch/record/1046852/files/p65.pdf
DrDu
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#9
Sep3-13, 06:05 AM
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P: 3,380
Quote Quote by UltrafastPED View Post
If a piezo only detects stress, and not pressure - then how can they make piezo absolute pressure gauges?
Typically, you have a piezoelectric membrane which separates the area with pressure p from some vacuum chamber. It is then clear that a change of pressure will lead to stress, too. However, I understood that the OP was asking for what happens if you bring a piezoelectric crystal completely into vacuum.
jf2086
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#10
Sep3-13, 06:41 AM
P: 4
Indeed, I was curious if there would be any stress due to expansion resulting in negative voltage.


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