| 摘要 |
PURPOSE:To keep the noise current suppressing effect for a long while, by coating the discharging top end portion of a rotor electrode made of an electrically conductive ceramic material with a metallic oxide such as a semiconducting material of CuO or the like. CONSTITUTION:The discharging top end portion of a rotor electrode 4 is coated beforehand with a layer of a metallic oxide like CuO or the like. The layer 5 is effective in preventing further oxidative degradation of an electrically conductive ceramic material, so that the production of noise current at the early stage can be prevented. Here, in order to form the coating layer 5 of a metallic oxide, it is also possible to connect a sintered metal 5A consisting of a metallic oxide of other semiconducting material of SnO2, V2O3, Ta2O3, NiO or the like. |
