Piezoelectricity

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August 6th, 2012, 05:24 AM
Elshan M

Piezoelectricity

Piezoelectricity effect generated by compression of certain materials. Due to compaction crystalline material releases electrical current.

Is there any relationship, dependence between the quantity of electrical charge or current and stress applied to crystalline?

I understand that piezoelectricity is the property of some materials. But there should be measure of amount of charge because of pressure applied to material. For example in all compaction pressures quartz mineral generates certain amount of charge or it depends and changes. Which of them is true?
August 6th, 2012, 05:22 PM
Kerling

No, Charge as you know is a conserved force. It doesn't just magically appear from nowhere out of the crystilline. But there is a charger seperation, to respective directions in respect to the pressure axis. This is minute and due to the change in pressure a small current will run through the crystilline. If this is possible. If not a electric field will be found but no current.
August 6th, 2012, 05:43 PM
Strange

Quote:

Originally Posted by Elshan M

But there should be measure of amount of charge because of pressure applied to material. For example in all compaction pressures quartz mineral generates certain amount of charge or it depends and changes. Which of them is true?

Are you asking if the charge is dependent on the pressure? If so, the answer is yes. This is used in piezoelectric sensors of various sorts (microphones, strain gauges).

Or are you asking if the same pressure will always produce the same charge? In which case, the answer is also yes. Although it may be slightly dependent on things that change the crystal structure (e.g. temperature, impurities, etc.)
August 7th, 2012, 02:40 AM
Elshan M

Quote:

Originally Posted by Kerling

No, Charge as you know is a conserved force. It doesn't just magically appear from nowhere out of the crystilline. But there is a charger seperation, to respective directions in respect to the pressure axis. This is minute and due to the change in pressure a small current will run through the crystilline. If this is possible. If not a electric field will be found but no current.

Ok. If we look at the voltage generated by pressure applied to crystalline then what kind relationshp will they have? I mean will it reciprocal, power function, or directly proportional or will it logarithmic....? I want to see the graphical relationship between pressure and volatage if it is possible
August 7th, 2012, 02:50 AM
Elshan M

Quote:

Originally Posted by Strange

Quote:

Originally Posted by Elshan M

But there should be measure of amount of charge because of pressure applied to material. For example in all compaction pressures quartz mineral generates certain amount of charge or it depends and changes. Which of them is true?

Are you asking if the charge is dependent on the pressure? If so, the answer is yes. This is used in piezoelectric sensors of various sorts (microphones, strain gauges).

Or are you asking if the same pressure will always produce the same charge? In which case, the answer is also yes. Although it may be slightly dependent on things that change the crystal structure (e.g. temperature, impurities, etc.)

I want to see the graphical relationship between pressure and voltage generated by this pressure. For instance we take the quartz and apply 100psi pressure and the voltage is gonna 10 v. then we increase the pressure up to 200psi the voltage would be what..... I mean, the first thing I want to figure out what kinf of relationship do pressure and voltage have in piezoelectricity effect, is it reciprocal function or logarithmic ext....The second thing, is to see the graph of that relationship at least for the pure quartz...
August 8th, 2012, 02:45 PM
Milan Karakaš

Quote:

Originally Posted by Elshan M

Piezoelectricity effect generated by compression of certain materials. Due to compaction crystalline material releases electrical current.

I am not an expert in this field, but I played a bit with ceramic piezoelectric elements. Such ceramic is made so that it has 'polarized state' of molecules, which after deformation (stress) produce specific amount of charge at electrodes. If load is applied to the contacts, such charge is transfered to the current flow, until stress is removed. During removing stress (pressure, for example), it produce charge (open circuit)/current (loaded circuit), but in opposite direction. It may behave as capacitor; if stress is applied, and in same time contacts are shorted, after removal of the short circuit we may release stress - piezoelectric element remain charged until charge is removed by load or by another short circuit.

Quote:

Is there any relationship, dependence between the quantity of electrical charge or current and stress applied to crystalline?

There is dependence, and manufacturer of such material may provide the specifications. Not sure about crystals.

Quote:

I understand that piezoelectricity is the property of some materials. But there should be measure of amount of charge because of pressure applied to material. For example in all compaction pressures quartz mineral generates certain amount of charge or it depends and changes. Which of them is true?

It is important to know how to cut quartz crystal in order to get useful charge (or current) depending of way how we deform (stress) it. I must admit that I don't know much about crystallography, and if needed piezoelectric material, I rather rely on ceramic transducers where manufacturer can give me the specifications.

(Sorry guys, this is my first post on this forum. I hope I did not make any mistake, and that my English is sufficiently clear.)