Permittivity measurement of thin dielectrics by using metamaterial absorbers inside a waveguide

A resonant method to determine the dielectric permittivity of thin films is presented. The method is based on a single reflection measurement and the unknown sample is used as a substrate of a ultra-thin metamaterial absorber transversally placed in a waveguide. The absorber is formed by a ground plane, the unknown sample and a multi-resonant frequency selective surface printed on a rigid known substrate. The real part of the dielectric permittivity of the unknown sample is estimated on the basis of the position of the resonant absorption peak whereas the imaginary part of the dielectric permittivity is a function of the absorption level. The main advantage of the proposed setup is the mechanical robustness (the sample is pressed between the FSS filter and the ground plane) which guarantees a high repeatability of the measurement.