Piezoelectricity: how do we measure it?

[markuz]

Hello everyone, I am running a physics class next week where I want to show to high school children the power of piezoelectricity.
I want to let them see with their own eyes that if a crystal is squeezed the differential potential between two opposite faces will change accordingly to the amount of deformation (load) the crystal undergoes. So I took off a bit of crystal from a gas lighter, connected to electrodes to opposite faces to measure the voltage with a multimeter.
What I found out doing the experiment is that the crystal do get charged as soon as the load is applied, but the voltage is rapidly decreasing (obviously because all the charge travel across the circuit to produce the reading); sometime it is so fast that I cannot get the reading at all. Anybody knows a better way to get such voltage gauge in such short amount of time (b.t.w. I am using both an analogue voltmeter and a multimeter to get the readings)?
Any suggestion appreciated.
Thanks

 

[UltrafastPED]

See this demonstration: http://vega.org.uk/video/programme/195

Search for "demonstration piezoelectricity" ... there were a lot of possible good hits.

 

[mikeph]

Not familiar with the level of voltage you get from one, but surely the voltmeter should present such a high resistance that the voltage is maintained? Are you saying the voltage is dropping because the charge is flowing through the voltmeter?

 

[markuz]

Right what I need is a (maybe cheap) oscilloscope

 

[russ_watters]

...and a source of vibration

 

[Redbelly98]

Right what I need is a (maybe cheap) oscilloscope

An oscilloscope will show a voltage change very easily. In ~cm sized, cylcindrical piezo devices I've used in the past, a 'scope on the 100 mV/div setting showed a several divisions deviation from squeezing the device by hand. Nice easy way to test that you have made good solder connections to the piezo.

...and a source of vibration

Squeezing by hand was always enough for me.