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Stray Capacitance Correction in Dielectric Cell Setup

When measuring low-capacitance samples, non-sample fixture elements—such as cell structural components, edge fields, and dielectric spacers—contribute parasitic capacitance. Without correction, these artifacts cause overestimation of the real permittivity ε’ and loss factor ε”

1. Constructing the Geometric Air Baseline

To measure background stray capacitance accurately:

  • Set up an empty sample cell using the exact electrode diameter intended for your measurement.
  • Insert identical dielectric spacers (or set micrometer positioning) to match your intended sample thickness (dd).
  • Clean all electrode surfaces thoroughly to ensure no conductive dust or moisture residues remain.

2. Measuring Realized Air Capacitance

  • Perform a broadband frequency sweep on the empty air-gap fixture.
  • Locate the flat, frequency-independent capacitance plateau between 100 Hz and 100 kHz.
  • Record this experimental capacitance value as Cmeasured, airC_{\text{measured, air}}.

3. Calculating Stray & Spacer Capacitance

  • In UniLab, open Sample Properties and enter the exact electrode diameter and spacer thickness to obtain theoretical air capacitance (C0C_0).
  • Determine stray capacitance using the formula: Stray + Spacer Capacitance=Cmeasured, air−C0\text{Stray + Spacer Capacitance} = C_{\text{measured, air}} – C_0
  • Enter the calculated value directly into the Sample Stray + Spacer Capacity field in UniLab.
  • UniLab automatically subtracts this offset from raw measured sample data, ensuring calculated dielectric functions (ε′,ε′′\varepsilon’, \varepsilon”) reflect purely the material under test.

This information, together with additional practical recommendations and measurement considerations, is covered in the complete guide for optimal measurement conditions with Eynocs Analyzers

Optimal Measurement Conditions Guide