Measuring Permittivity of Thin Film Materials for Spacecraft Charging Applications

Permittivity measurements of <500 µm thin film polymeric samples demonstrated an asymptotic thickness dependence. For ~25 µm samples the observed permittivities were as much as 50% less than bulk measurements. An in-depth analysis of data sets of four common polymeric materials led to an empirical single-parameter model based on an effective stray capacitance to compensate for instrumental effects. This proposed model gave values consistent with bulk measurements for samples ~10 µm to >1000 µm and across frequency ranges from ~100 Hz to >10 MHz. The model was then applied to a set of thin film spacecraft materials, which are most commonly used as thermal control blankets or electrostatic shielding. These materials, whose thicknesses range from ~10 µm to ~100 µm, originally gave nonphysical results., The corrected results, using the proposed model, largely agree with bulk values of permittivity for the core polymeric materials of the composite films. These more accurate values of permittivity will allow better predictions of spacecraft charging effects and arcing.