Measurement of complex dielectric constant of Al2O3-TiO2 and Cr2O3 plasma spray coatings between 75 and 220 GHz

Plasma-sprayed coatings on metal substrates are often used to absorb radiation for high-power applications in the millimeter-wave range [1]. ISTP-CNR (formerly IFP-CNR) has used plasma-sprayed coatings for many years in high power bolometric loads for millimeter waves [2]. Literature on electromagnetic properties of the coatings is sparse in this frequency range. This paper reports measurements on the same samples of Al2O3(40%)+TiO2(60%), Cr2O3 used in [3] over an extended frequency range, including frequencies of interest for diagnostics on the JT60SA tokamak [4]. TiO2 samples were measured too, but they are too thick for extracting useful information from the measurements with the method used in this paper.