Crystal Question

[tgeorge]

Do crystals, when feeling a CONSTANT (non varying)pressure/force emit a current? I have a suspicion that as the crystal is pressed inwards current will be emitted but will die off. If so, this is the case, where can I read about this variable pressure/voltage relationship of crystals?

Very basic question I realize, but my specialty is Industrial Engineering, and I have a project that is a bit outside of my focus.

 

[Skogsgurra]

What happens in a piezoelectric transducer (there are other types than crystals - ceramic ones are a lot more effient) is that there is a charge build-up when you press it. The charge is proportional to force and is usually measured in picocolumbs or nanocolumbs.

The charge leaks away slowly and that's why you cannot do static measurements with a piezoelectric transducer. There are piezoresistive transducers, though, that can be used for static measurements. The more common one is the strain gaugue.

Gunnar Englund

http://www.gke.org

 

[Comcokid]

Look up "piezoelectric effect". A crystal under constant pressure generates no voltage. However, any compression or strain of the crystal, arising from vibation or external forces, will generate a voltage that varies with the vibration or strain. A step-change in strain will generate a voltage that will then bleed-off depending upon leakage, etc.

In like fashon, a voltage applied to a crystal will cause it to deflect.

 

[tgeorge]

Thanks guys.

 

[Warpspeed]

The easiest way to think of this, is as being like the voltage change on a very small value capacitor. The voltage is certainly there, and it may be fairly high, but as you try to measure it, it will very rapidly leak away.

Try doing a Google on "charge amplifiers"