Lossy Flange for Open-Ended Rectangular Waveguide Materials Characterization

Open-ended rectangular waveguides are widely used for near-field measurements and in particular for microwave nondestructive testing (NDT) applications pertaining to materials characterization. This method is capable of simultaneously evaluating the thickness and material properties of various layers within multi-layer dielectric structures and composites. After collecting measurement data, a full-wave electromagnetic model is used to calculate the estimated properties of the structure. One of the electromagnetic constraints considered by the model (i.e., an infinite flange) is practically satisfied using an engineered flange. However, the engineered flange has certain limitations when dealing with certain layered structures, namely; those that are conductor-backed and electrically thin. In such cases where the measured response cannot be replicated by the electromagnetic model, there is significant error in thickness and material property estimation. This work presents the use of a lossy dielectric material as an engineered flange cover for performing open-ended rectangular waveguide measurements specifically for use on such structures through the use of a lossy flange cover. The performance of the engineered flange with and without a lossy flange cover are compared through electromagnetic simulation and measurement of thin and conductor-backed structures.