Dielectric properties of materials using whispering gallery dielectric resonators: Experiments and perspectives of ultra-wideband characterization

Measurements for the determination of the complex permittivity of liquid an d solid materials based on the use of whispering gallery (WG) dielectric re sonators are presented. The procedure implies the measurement of the electr omagnetic parameters of the involved resonator interacting with the materia l under study. The field distribution in the different WG resonant modes wa s obtained by an analytical calculation under the mode matching method appr oximation. The results of this calculation, combined with the experimental data, well account for the values of the complex permittivity of materials of interest. Due to the peculiar properties of WG resonators, the method sh ares the advantages of the wideband systems with the sensitivity and accura cy of the resonator systems in dielectric measurements. Dielectric permitti vity of alumina (Al2O3) and of cyclohexane is measured in the frequency ran ge 18-26 GHz. The overall accuracy of the measurements is discussed and the different sources of errors analyzed. Specific attention is paid to the me asurements of variations of dielectric properties to monitor some physico-c hemical processes. Finally, preliminary measurements at hundreds of GHz sho w that the procedure is particularly useful for study of dielectric propert ies up to the THz frequency region. (C) 2000 American Institute of Physics. [S0021-9606(00)50205-0].