In situ microwave characterization of nonplanar dielectric objects

In this paper, a novel experimental solution is presented for the nondestru ctive, noncontact, and in situ characterization of dielectric objects of cu rved shape using a spot-focused free-space measurement system. Measurements were made on Plexiglas and glass samples of cyclindrical shape with differ ent radii of curvature, and the complex permittivities were computed from t he measured S-21 and S-12. Comparing the results with planar samples show t hat the curvature does not significantly affect the accuracy of the measure d permittivity of cylindrical surfaces if the radii of curvature are large compared to the size of the focusing spot. Results for a number of curved s amples agree with the published data and this demonstrates the usefulness o f a spot-focused free-space system for in situ characterization and evaluat ion of materials and complex structures during processing and fabrication. The other benefit of this approach is the noncontact nature of the method, which permits measurement of solids and liquids in high-now-temperature env ironments. The spot-focused beam permits characterization of small or large samples.