High-Temperature Measurements of the Microwave Absoprtion Coefficient in Ceramic and Composite Materials

We measure the microwave absorption coefficient in ceramic and composite materials in a wide temperature range. The measurement method is based on comparing the intensities of the electromagnetic radiation in the working chamber of a gyrotron facility in the presence and absence of a specimen in it. It is shown that if the dielectric constants of components of the composite materials are known, one can determine the dependence of the dielectric loss tangent on the temperature of the material. We obtain the temperature dependences of the dielectric loss tangent at a frequency of 24 GHz for alumina ceramics with the Al₂O₃ content exceeding 99.5% in the temperature range 200–1100°C and for the Al₂O₃–ZrO₂ composite with the Al₂O, ZrO₂, and Y₂O₃ contents equal to 88%, 11%, and 1%, respectively, in the temperature range 200–600°C.