# Compression on Piezoelectric crstals

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1. Jun 6, 2015

### SmritiB

Can piezoelectric crystals produce electricity from compression only ? When continuous compression and tensile forces on them generate AC voltage source, can only compression force give me a DC voltage source ? Is there a chance that the crystal will initially act as a Voltage source but soon re-adjust itself to get its acquired polarity neutralized ? If so, how long typically can the polarity last ? And I would also be glad if i could get some data for my project. specifically: 1.What is the minimum pressure required for any piezoelectric crystal to generate electricity ?
2. How much Volts can i expect from that pressure?

2. Jun 9, 2015

### tech99

No one has answered you. I think the piezo crystal acts like a small capacitor, so the voltage which is developed is stored across the two surfaces, and eventually it will leak away. The available energy is stored in the capacitor, 0.5 CV^2. Some crystals can give high voltages, sufficient to spark, as with a gas lighter, and others are used for microphones, where the faintest sound still generates a few microvolts. Quartz is used for stable piezo resonators for electronics. I don't think there is any one-way action, and tension, compression and bending will all generate a voltage.

3. Jun 9, 2015

4. Jun 9, 2015

5. Jun 9, 2015

### rumborak

I'm too lazy to do it right now, but boy that Wikipedia chapter needs some editing. Some dude essentially used it for self-promotion.

6. Jun 12, 2015

### SmritiB

7. Jun 12, 2015

### rumborak

All those things of course increase the output (up to a point of course, you can't just arbitrarily raise the pressure on a piezo and expect linear response all the way).

The key constraint however is that static pressure creates static voltage, but that static voltage, kinda like a charged capacitor, can't do much work because it quickly becomes equalized with the rest of your circuit. Piezos don't work like batteries which can continuously push electrons. After all, piezos don't actually conduct electricity, so you can't have a circuit like with abattery.
The moment you connect something to a piezo, just like the moment you connect something to a charged capacitor, the piezo will lose voltage differential.

So, the only way to continuously extract power from a piezo is through varying pressure, I.e. vibration.

Last edited: Jun 12, 2015
8. Jun 25, 2015

### SmritiB

I see, Thanks a lot.