A non-invasive permittivity measurement based on split-ring resonators at microwave frequencies

In this paper, we introduce the microstrip-line-excited spilt-ring resonators to the permittivity measurement at microwave frequencies. The samples with specified thickness are placed on a well designed sensor, so that relatively large frequency offsets due to the samples can be detected to retrieve the permittivity. Analysis and experimental measurements validate that by applying this method, permittivity can be linearly retrieved from the measured frequency offsets. The measurement setup can be conveniently calibrated with a given sample with known permittivity.