. . "In this specific example, a quartz whose thickness is 1 mm is used as the dielectric material shield 32 a made of insulator, but it is possible to use, as a material for the insulator, a material such as alumina, aluminum nitride, and the like, having a low dielectric constant and a high resistivity, each of which is selected from a ceramics dielectric material group superior in the heat resistanc" . . .