Do piezoelectric materials produce a current flow or just an electric field?

Question

I was watching a video https://www.youtube.com/watch?v=uvT3XvDSSQw about piezoelectric materials.

They mentioned that "a current can flow when a pressure is applied to the material".

I have a problem with this expression. I'm not sure if my confusion is in its place.

I know that when a stress is applied on a piezoelectric material, it will generate an electric field due to the dislocation of the electric charges/ creation of electric dipoles.

But that doesn't mean that a current should flow from the material, because if a current flows, that means the material has lost electrons, therefore has lost some mass.

And in case it was true that the electrons were leaving the material instead of just emitting their electric field while still being connected with the materials molecules, then I think what they mentioned about connecting the material to a circuit and measuring the current flow will make sense.

Answer 1

The quartz or other Piezoelectric materials do not work under constant compression, they work under the varying pressure or vibration of the crystal. So they don't lose electrons. They produce an alternating electrical field.

If you apply constant pressure they just go through a very short time of polarization then stop producing the electrical field. But if you apply vibration the electrical field can create a small AC current.

The small voltage is then amplified.

They can also produce ultrasound in reverse piezoelectric action if supplied with a certain electrical frequency and are used for medical purposes. source

Answer 2

the output signal of a stressed piezoelectric crystal is primarily a measurable voltage accompanied by an almost too-small-to-measure current flow. This is a general characteristic of high-impedance devices, of which the crystal is a good example.