1
$\begingroup$

I have done the measurements of paralle plate capacitor with HM8018 LCR meter to measure capacitance and later, with known parameters such as surface area and separation distance, calculate permittivity of the dielectric.

I have two copper plates as electrodes and multiple 4.5mm thick dielectric plates. I have done measurements starting with one dielectric plate up to 9 plates.

When calculating permittivity, it shows significant increase in permittivity with added dielectric plates (2.13 with one plate, 8.69 with 9 plates). I have found that it has to do something with the plate count (possibly some polarization effect) but wanted to ask your opinion on this as I couldn't find such problem discussed when searching for it.

Hope I explained the problem good enough to understand, and I would appreciate if anyone could help me with this.

Measurement table:

enter image description here

enter image description here

$\endgroup$

1 Answer 1

0
$\begingroup$

You have not subtracted out the cable+stray capacitance, so the capacitance reading on the meter has a constant offset. Here is a plot of your data, showing the extrapolation to the plates held infinitely far apart, which should result in a measurement of zero capacitance on your meter:enter image description here

$\endgroup$
5
  • $\begingroup$ Taking into account the cable capacitance (taken to be around 100pF/m) the offset would be around 15pF for 15 cm cable. That would just contribute to value of calculated permittivity not the growing trend. With cable capacitance taken into account the new permittivity values are 1.88 with one plate and 6.4 with 9 plates. $\endgroup$
    – PorinsR
    Feb 11, 2021 at 9:16
  • $\begingroup$ Can you show the data: your measured capacitance for each stack. I will plot it. Maybe it will make more sense how the trend comes about (because, yes, an offset capacitance does cause an increasing trend in extracted permittivity). $\endgroup$
    – Richold
    Feb 11, 2021 at 17:46
  • $\begingroup$ Sure! I have added measurement and calculation table in the original post. $\endgroup$
    – PorinsR
    Feb 11, 2021 at 23:15
  • $\begingroup$ I did the calculations with the offset capacitance 48pF and the results now looks reasonable - permittivity is 1.32-1.42 which could be explained with air between the plates. $\endgroup$
    – PorinsR
    Feb 12, 2021 at 7:36
  • $\begingroup$ Yes - air is always a factor. That is why PCB manufacturers who want to measure the permittivity of their substrates press the stack together under some pressure. See microwavejournal.com/ext/resources/images/Figures/2019/May/5M31/… $\endgroup$
    – Richold
    Feb 12, 2021 at 14:13

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.