Strongly perturbed cavity resonators as tools for non-destructive in-situ material parameter measurement

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According to the state of the art, electric material parameters at GHz frequencies are measured by, amongst others, the cavity perturbation method. In doing so, one compares the measurable resonator characteristics with and without material sample in the cavity and assumes but a small perturbation by the sample and the required coupling of the resonator to the measuring environement. If one could monitor, for instance, loose materials, fluids, and catalysts in their process environments, many processes could be run more efficiently energy-wise, more environmentally friendly, and more economically. With these potential applications, several assumptions of the cavity perturbation method are violated. In particular, one cannot freely design geometries and select materials inprocess installations. One rather faces large, inhomogeneous, lossy, anisotropic, and time-varying fillings and (depending on the resonance mode and the material parameters) a strong coupling to the measuring environment. In theses cases, the resonator is stronglyperturbed. Even in simple cases (homogeneous, but quite lossy resonator filling), there is currently no feasible way of extracting the characterisctis of the uncoupled resonator, which are of interest because they mirror the properties of the material sample, from the measurable characteristics of the coupled resonator. The current project aims at laying the foundations for the measurement of electrical material parameters by the cavity perturbation method in those instances in which the usual assumptions are violated. To this end, it is vital to eliminate the effect of the coupling on the resonance characteristics.