Retro-Modelling Technique for Permittivity Measurements in the Range from 2.2 to 2.6 GHz for Medical Applications

In this study we present a permittivity measurement technique based on retro-modelling of a resonant cavity in the frequency range from 2.2 to 2.6 GHz that allows for a more arbitrary sample shape than traditional cavity perturbation techniques. It is shown that the resolution of the retro-modelling technique can be improved if the invoked modes in the sample and in the surrounding cavity space are of different type or indexation, a condition that must clearly be avoided in classical perturbation techniques. The measurement method was applied to a ceramic sample of unknown permittivity which was retro-modelled to $\varepsilon^{\prime}=19.35$ and $\sigma=0.009S/m$ with a remaining combined error of geometry and permittivity deviations between measurement and simulation of <0.1 % in frequency and 22% in Q-value at the target resonance. This technique will allow us to identify suitable dielectric materials to improve the feed efficiency of our magnetic field applicator which is currently being developed for microwave breast cancer detection.