Question on capacitor spacing, capacitance and admittance

Thread Starter


Joined Jul 5, 2020

I have developed a setup that tries to determine the height change of a sample by placing it in between two capacitor plates. The sample itself is not part of the capacitor but the height translates to the spacing of the capacitor plates. The dielectric medium is helium, and the setup is placed in a gamma radiation field and temperatures will increase up to 500 deg C.

Now, before I start an experiment (no gamma, no increased T), the capacitance is 3-4 pF, i.e. exactly what I expect based on plate distance at RT and the admittance is in the order of a few to <1 nS. Now with the start of the experiment (so gammas and 500C), the capacitance drifts towards 14pF, in a same way the admittance drifts to 10000 to 16000 nS. The frequency is adjustable but fixed at 20kHz for now.

at first this seems counterintuitive, as I expect the capacitance to go down with increased admittance...

Is there a way to correct the capacitance for this observed admittance, maybe when a trend is established, of frequency vs admittance?

Kind regards