Microwave Measurements for Conductive Anisotropic Materials

Applications of anisotropic composite materials range from construction composites to electric circuit boards. Anisotropic conductivity is one of the many important measurands for anisotropic composites for identifying misalignment. However, there are only a few nondestructive, noncontact techniques available. Here, we explore waveguide ellipsometry, a new electromagnetic characterization technique, and its application to conductive anisotropic composites. We demonstrate waveguide ellipsometry and discuss the design and implementation of a novel rotation test head on a robotic arm. To validate our technique, we designed and fabricated test wafers with ideal anisotropic composites consisting of gold stripes on materials with varying sheet resistances. The measurements were compared to full-wave simulations with simulated material properties extracted with the help of composite theory and simple circuit analysis. We found a good match between the simulated and measured complex scattering (S-) parameters for all test wafers fabricated with molybdenum disilicide (MoSi2) and gold stripes. Finally, we map the measured S-parameters to simulated S-parameters with help from composite theory and circuit modeling. Broader impacts of microwave ellipsometry include in-line measurement and conductivity imaging of large-scale and 3-D parts for nondestructive evaluation.