Dielectric glue?

[antknee]

I have an ultrasonic atomiser. You can see a picture of it above, you vibrate it at its resonant frequency and some mist appears. It has three parts, 1) pzt, which will vibrate 2) a steel ring upon which the pzt is glued and 3) a central foil with holes, which is glued to the steel ring and which will throw out liquid as mist.

The whole unit has a static capacitance of 1.8nF. When I take the pzt off the steel and measure the pzt capacitance alone, it is 0.2nF. When I glue the pzt back on the capacitance stays at 0.2nF...I've glued the pzt back on with conducting paint and superglue but the capacitance stays at 0.2nF.

My questions are: Was the original glue some kind of dielectric? I'm not sure what is going on exactly. Is it possible to buy dielectric glue?

Regards,

Antknee.

 

[Sceadwian]

Has the function of the unit altered at all? The values you're talking about are so low you haven't even mentioned why you need such a specific capacitance in the first place. From what little I can tell of the picture the center of the piezo is attached directly to a wire, and the second wire is attached to the steel ring, so you need to attach the steel ring to the rest of the piezo disk with something that conducts, was it soldered?

 

[antknee]

I want to repair the piezo. At 0.2nF the drive circuit no longer works.

All 3 parts were glued together with what appears to be the same glue. The pzt has both terminals on one side but some foil takes one terminal to the under side of the pzt.

Thanks.

**broken link removed**

 

[antknee]

I've spent the last hour searching to try to find an adhesive that would increase the capacitance of the pzt. I searched electronic suppliers, googled the terms dielectric glue and capacitive glue and anything similar sounding.

But alas I can't shed light on this. Even if you don't know for sure can you give me a pointer?

Thanks.

Antknee.

 

[MikeMl]

Are you sure that the increased "capacitance" is not due to changing the mass of the piezo? (Look up motional capacitance) read here

 

[antknee]

Hi Mike,

If i put the unit back together with different glue, silver paint say, it has the same mass as the original unit, but the capacitance stays at 0.2nF. The only variable seems to be the glue. Also these are static values, measurements taken away from resonance so there isn't much vibration/motion.

That link is very interesting. I am reading it right now. It seems to say as the capacitance has changed the resonant frequency of the unit has also changed. Which would explain why it doesn't work any more!

Thanks,

Antknee.

 

[antknee]

I had enough of caring, so chucked it away. I'll buy another! Thanks Mike and Sceadwian.

 

[Sceadwian]

Also these are static values, measurements taken away from resonance so there isn't much vibration/motion.

Which means the number you were getting meant absolutely nothing. You threw out a perfectly usable piezo transducer more than likely.

 

[antknee]

It is standard practise to measure the static capacitance of a piezo. A piezo is electrically modelled by a static capacitance in parallel with an LCR. The static capacitance has to be included in the drive circuit and matched to the LCR for best power transfer. Either some obscure glue is being used or the piezo is damaged somehow, perhaps it has a crack I can't see. I don't know.

Thanks.

Antknee.