Scanning Microwave Ellipsometer And Performing Scanning Microwave Ellipsometry

Abstract

New strong, light, and compact formed carbon fiber components require shorter, higher-aspect ratio carbon fibers. Shorter carbon fibers must be aligned to realize the desired tensile strength. Before this invention, industry lacked a tool to characterize carbon fiber alignment for inline quality assurance or for verification of alignment in 3D parts. This invention solves that problem through the implementation of scanning microwave ellipsometry. The implementation uses a polarized electric microwave field and measures the reflection of that field off of a sample-under-test as a function of angle. The resulting reflected power plotted versus measured angle on a polar plot can have an elliptical shape. Leveraging this idea, we designed a test head that rotates the electric microwave field relative to the sample without rotating the sample. To raster the test head over a sample, we placed the test-head on a 6-axis robotic arm. To use this implementation, we wrote an algorithm that fit the microwave ellipsometry data. The algorithm produces four discrete measurands that can be plotted as a function of position in three-, two-, or one- dimensions. The measurands are the maximum value, the minimum value, the alignment value, and the orientation value. While the target application is directed at carbon fiber, scanning microwave ellipsometry to industrial materials is broadly applicable to any use case where large-scale imaging of material properties is useful.