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E4980A with 16451B dielectric test fixture

Question asked by mechemems on Jun 3, 2014
Latest reply on Jun 5, 2014 by algoss
I have a E4980A LCR meter with a 16451B attachment for testing the dielectric constant of materials. I am using it to characterize some polymers, but have performed some sanity-check by simply measuring the permittivity of air, just to confirm everything is in order. I am finding, however, that I am getting unexpected results. Basically, the permittivity should be a constant 1 for all gaps, but the measurements are telling me that it increases with gap. This is shown in the attached plot. 

Any suggestions on things to look at? I perform a short correction, but this is just an offset. I'm a little perplexed because if it were simply an offset, that isn't as big a concern, but I am concerned by the fact that the measurements tell me the permittivity of air would be changing with gap. I've looked through the manual and see that there is a table on page 3-61 that can be used to make area corrections, but this correction is relatively small compared to the issue I am seeing.

I appreciate any suggestions.