Two-layered disc quasi-optical dielectric resonators: electrodynamics and application perspectives for complex permittivity measurements of lossy liquids

Electromagnetic properties of novel quasi-optical resonators are studied theoretically and experimentally. The resonators are a radially two-layered dielectric disc sandwiched between conducting endplates. The internal layer can be filled with air or lossy liquid. Whispering gallery modes are excited in such a resonator and the mode energy is concentrated near the inner side of the cylindrical surface of an external layer. The measurement data obtained in the Ka-band are compared with theoretical calculations of eigenfrequencies and quality factors of the Teflon resonator filled with water, ethyl alcohol, benzene and aqueous solutions of ethyl alcohol. A number of 'anomalous' properties of the resonator can be described using Maxwell equations. The experimental data on the complex permittivity of a binary mixture water-ethyl alcohol are compared with the values calculated in terms of Debye's function. An important feature of the proposed technique is that it holds promise for making first principle microwave measurements of the permittivity of lossy liquids.