Frequency and time domain permittivity measurements on solid CO2 and solid CO2 - soil mixtures as Martian soil simulants

Abstract

Permittivity, and conductivity measurements were performed to assess the dielectric behavior of solid CO2 (i.e., CO2 ice, snow, and powder) and solid CO2/soil mixtures. For comparison, some dielectric measurements were also conducted on H2O ice, dry glass beads, glass beads saturated with water, drained glass beads, and frozen drained glass beads. The measurements were performed in the frequency domain (20 Hz to 1 MHz) using a capacitive cell (Parallel Plate Capacitor) and in the time domain using a transmission line (Time Domain Reflectometry). The data obtained with both techniques have shown that solid CO2 has a permitivity value that ranges between 1.4 and 2.1 as a function of density, values that distinguish it from H2O ice. In contrast, H2O ice, dry glass beads, frozen (drained) glass beads, and dry volcanic sand all have very similar permitivity values, and thus they cannot be clearly distinguished at higher frequencies. Data have also shown that a high volume fraction of solid CO2 significantly reduces the permitivity value of a soil. Furthermore, almost all the samples tested in this work seem to behave like low loss materials, having a conductivity which is generally equal to or lower than 10-6 Sm-1 at the highest frequency (and smaller values at lower frequencies). Finally, TDR measurements and data from some dielectric models were compared in order to assess the capability of these models to predict the permittivity of a granular multiphase material.