A contactless measurement of the surface impedance of a thin sheet of material

Surface impedance value represents a crucial parameter for the characterization of thin sheets of material. A method for the estimation of this quantity that does not require a direct contact with the sample under test is proposed. The surface impedance is calculated through an inversion procedure that exploits the scattering parameters obtained from the proposed waveguide measurement setup. An inversion procedure based on the representation of the waveguide-air section-waveguide section as a T junction is employed. It is also shown that the absence of contact of the sample under test and the waveguide determines the leakage of electric fields which invalidate the inversion procedure. An improved configuration including an electromagnetic band-gap (EBG) structure is used to make the estimation of the surface impedance more accurate.