Hello guys, I\'m unsure of which way the voltage is created when a stress is app

Question

Hello guys, I'm unsure of which way the voltage is created when a stress is applied.

As I understand it, P = dT; and since V=Q/C; I suppose the voltage should be in the opposite direction of the Polarization vector. My main confusion is about the relationship between P=e0XE. What exactly does this mean in terms of the piezoelectric effect. I thought the only way for E to exist, is if there is an External field applied to the crystal. So in this case, there isn't. E=E0/er.

So I'm confused, does this mean that this relationship doesn't hold inside a piezoelectric crystal?

Thanks

Explanation / Answer

In a piezoelectric device, mechanical pressure causes charge separation in the atoms of the piezoelectric material. The dielectric material in a capacitor uses simply an applied voltage to do so. If the material is compressed, then a voltage of the same polarity as the poling voltage will appear between the electrodes, if stretched, a voltage of opposite polarity will appear. here the second drawing is correct for the question asked. follow the below mentioned link for more details. It might be helpful: http://www.ippt.gov.pl/~tzielins/doc/ICMM_TGZielinski_Piezo.slides.pdf

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