New developments on automated-active circuits for permittivity measurements at microwave frequencies

The complex permittivities of porous ceramics made up of zirconium and silicon oxides having pore diameters from 0.9 to 5 μm and filled with water are measured by computer-aided testing (CAT) while each sample is heated by microwave power. The complex dielectric permittivity is calculated by the well-known cavity perturbation formulas and the cavity measurements are obtained by the automated active cavity perturbation technique operated at high power levels (20 W). Automated weight measurements on the samples during testing makes it possible to accurately relate the permittivity values to the residual moisture in the heated samples