Control of dispersion frequency of BaTiO3-based ceramics applicable to thin absorber for millimeter electromagnetic wave

Elements such as B, Li and Na were doped to barium titanate, BaTiO3 in order to control dielectric dispersion. Addition of 3 mol% Li2O lowered the dispersion at frequency of 0.53 MHz, while addition of 3 mol% B2O3 or Na2O did not affect dispersion frequency. BaTiO3 doped with 0.3 mol% Li2O showed dielectric dispersion at around 2.5 GHz. An electromagnetic (EM) wave absorber using the doped BaTiO3 plate was tried to produce for millimeter frequency range. A matching layer of 0.5 mm thick ceramic plate with relative permittivity 21 was attached to it to suppress reflection of incident EM wave due to the discontinuity at the boundary between the BaTiO3 and air. The obtained EM wave absorber had reflectivity of −45 dB at 31 GHz and −25 dB at 95 GHz, respectively.