Non-destructive complex permittivity measurements of absorbing materials

A flanged circular waveguide propagating dominant TE₁₁ mode is used to test absorbing properties of a plate-shaped dielectric sample placed at the opened waveguide end. In this method, which is a non-destructive local one, the material complex permittivity ε\´-ε" is evaluated from vectorial reflection coefficient measurement. Associated to a test set up, compatible software which numerically computes vectorial reflection coefficients Γ and automatically constructs ε\´ and ε" charts as a function of Γ has been developed. The influence of different measurement parameters on chart characteristics has been shown to yield the permittivity in optimal conditions and to make this method fast, easy to use, and as accurate as possible. Many absorbing materials have been tested using this non-destructive technique. The results are in good agreement with those obtained using the well-known loaded rectangular waveguide method