High-temperature dielectric characterisation in the S-band using a solar simulator heated re-entrant microwave cavity and multiphysics modelling

This study presents a comprehensive system for the high-temperature microwave characterisation of dielectric materials. This system addresses the current scarcity of reliable dielectric data above 1000 °C, particularly under concentrated solar irradiation. A solar simulator comprising seven xenon arc lamps delivers highly focused energy, enabling rapid temperature ramp rates and temperatures in excess of 1000 °C. Small samples are heated directly within the resonator via solar heating, and the permittivity and loss tangent are extracted in the S-band (2–4 GHz) using a specially adapted re-entrant cylindrical cavity. The cavity is produced using additive manufacturing, is internally gold-plated, and incorporates an integrated cooling system to ensure operational stability under extreme thermal loads. A multiphysics algorithm based on COMSOL simulates the coupled thermal and electromagnetic behaviours, accounting for the effects of cavity expansion and temperature-dependent conductivity that are often neglected in high-temperature measurements. Experimental results obtained with alumina samples demonstrate good agreement between simulations and measurements, showing an increase in effective permittivity with temperature. These results highlight the potential of the proposed platform for accurately characterising dielectrics in extreme environments. However, further refinement is required for the precise estimation of the loss tangent and associated uncertainties.