Dielectric properties of natural grown tourmaline at 100 GHz

CVD diamond is a well known excellent low loss material (tan δ = 0.55 · 10^-5) for microwave transmission e.g. in fusion reactors for the ECRH&CD system. Goal of our investigation is to find out other natural dielectric materials with even low loss tangent properties. Tourmaline is a complex structured natural mineral which grows in large crystals. A disk, sliced perpendicular to the c-axis of the crystal lattice, was used to determine the loss tangent and the dielectric constant in the 100 GHz frequency range.