Electromagnetic properties of sapphire, ruby, and irradiated ruby at frequencies of 30–40 GHz

Permittivity and electromagnetic losses of sapphire, ruby, and irradiated ruby samples were examined at frequencies of 30–40 GHz and temperatures of 4–300 K employing the whispering gallery mode technique. At room temperature, the dielectric properties of the sapphire, ruby, and irradiated ruby samples were similar. Significant differences in electromagnetic losses took place at cryogenic temperatures. Losses were related to the imaginary part of the susceptibility associated with the presence of paramagnetic Cr³⁺ ions as well as those introduced by structural defects caused by the irradiation of ruby samples. The presence of impurities and the structural defects result in the dielectric losses being larger than those of pure sapphire.