Determination of microwave permittivities using a metallic slit

A procedure for determining the microwave permittivity of small quantities of material is described. A single metallic slit is built comprising a pair of 3 mm thick aluminium plates separated by spacers of less than 100 mum thickness. The material to be characterized fills the space between the two plates and the slit is inserted in an absorber aperture. When microwaves are incident on this structure with their electric field perpendicular to the cell walls a set of Fabry-Perot-like resonant transmission peaks is recorded as a function of incident wavelength. By using these Fabry-Perot-like resonances a fast and easy-to-use procedure for determining the permittivities of materials in the microwave region has been developed. To demonstrate this technique, the microwave permittivity of four different materials, some of which may otherwise be difficult to characterize, have been determined at the microwave region (50.0-75.0 GHz).