Materials Characterization Using Microwave Waveguide System PDF Download

"Nondestructive evaluation of stratified (layered) composite structures at microwave and millimeter wave frequencies is of great interest in many applications where simultaneous determination of the complex dielectric properties and thicknesses of multiple layers is desired. Open-ended rectangular waveguide probes are effective tools for this purpose. The technique requires a full-wave electromagnetic model that accurately calculates the complex reflection coefficient as a function of frequency and material properties. Subsequently, this information is used in conjunction with the measured complex reflection coefficient to evaluate the sought for material properties. This thesis presents simulated and measured data to investigate the influence that measurement system noise, which contaminates the measured complex reflection coefficient, has on estimating material properties. It will be shown however, that the foremost contributor to errors in estimating material properties is not due to system noise, but rather, is due to an inconsistency between the electromagnetic model and the measurement setup. More specifically, the electromagnetic model assumes an infinite waveguide flange while measurements are conducted using a finite-size flange. Consequently, the results of the model and those from measurements may not be sufficiently alike for accurate dielectric property and thickness evaluation. The work presented here investigates the effect of using an open-ended waveguide with a standard finite-sized flange on the error in evaluating the complex dielectric properties of a composite structure. Additionally, the design of a novel flange that markedly reduces this undesired effect by producing very similar electric field properties, at the flange aperture, to those created by an infinite flange will be presented and verified in measurement"--Abstract, page iii.