Resonant Atmospheric Plasma-Sprayed Ceramic Layers Effectively absorb Microwaves at 170 GHz

Microwave absorbing layer materials (MALMs) are extremely important for many components in fusion reactors to absorb microwave radiation in a controlled manner and with predictable power density. Therefore, a detailed knowledge of absorption properties of absorber coating materials used is necessary. Plasma-sprayed mixed oxide coatings are most commonly used in those applications where moderate power density is expected. In this paper, a plane wave absorption model is presented using refractive index and absorption coefficient as internal parameters and incidence angle, polarization, and layer thickness as external parameters. The model has been calculated assuming radiation of 170 GHz, as envisaged for the ITER research facility. Three atmospheric plasma-sprayed coating materials were considered in this work: titanium dioxide (TiO 2 ), chromium oxide (Cr 2 O 3 ), and a mixed aluminum-titanium oxide Al 2 O 3 -TiO 2 (40/60). Theoretical results are compared with free wave measurements with two antennas. Different coating thicknesses have been prepared and measured in different polarization and incidence angles. Results are discussed regarding polarization, incidence angle, layer thickness, absorption coefficient, and refractive index.