A New Experimental Setup for High-Temperature Dielectric Characterization of Venus Analogs

Abstract

Radar sounder investigations of Venus' crust are particularly challenging, due to the expected high loss character of the rocks at temperatures of hundreds of degrees. The dielectric behavior of hot planetary analogues is poorly understood, as the procedure to measure such samples is difficult, especially in the frequency range of 1–100 MHz typical of planetary radar sounders. In this paper a new experimental setup capable of measuring the complex dielectric permittivity of rock slices at temperatures as high as $500°$C, in a large frequency range is presented. The measurements are based on the open-ended coaxial transmission line approach, where the sample is kept inside an oven to reach thermal equilibrium, and the probe tip is placed in contact with the rock and rapidly removed to limit heat propagation along the probe. The dielectric quantities (real part of permittivity and loss tangent) are computed by inverting the scattering parameters measured with a Vector Network Analyzer. Experimental data are compared with electromagnetic simulations, to define the probe characteristics and its criticalities. To assess the reliability of the setup, the results are validated using Macor ceramic samples for which dielectric properties have been measured and certified at different temperatures and frequencies. The methodology is then applied to a basaltic rock sample to demonstrate its applicability to potential Venusian analogues. The proposed technique instills confidence in the possibility of exploring the complex permittivity parameter space of many igneous and sedimentary rocks at high temperatures.