Abstract
Loss factors of ceramics are very important to heat ceramics by microwave energy for sintering or melting. Dielectric properties of ceramics at 6GHz are accurately measured by the use of a rectangular cavity and the perturbation method on various kinds of ceramics at room temperature. The measured values of dielectric constant and loss factor are in good agreement with literature values. A new method is presented to measure dielectric properties of ceramics in high temperatures above 1500°C. A ceramic sample inside the cavity is heated by microwave energy, and its dielectric properties are measured by detecting both the iris width and the plunger position controlled to give the resonance with critical coupling. Dielectric properties of alumina are successively measured by this method in the temperature range up to 1800°C. The loss factor of alumina (92% purity) begins to rise rapidly above 600°C and the value at 1800°C is approximately one hundred times larger than that at room temperature.
