Opportunities and challenges in the characterization of composite materials in waveguides

The effective properties of a composite material can be computed from knowledge of the component materials and the geometry of the microstructure. To verify these results at a certain frequency, wave scattering experiments can be performed, where typically reflection and transmission data are recorded and subsequently analyzed in a theoretical scattering model to extract material data. In this paper, we show that the wave scattering experiment is more closely related to the wave parameters (wave number and wave impedance), than to the material parameters (permittivity and permeability). We focus on anisotropic materials, demonstrate a method to extract the effective permittivity of such materials, and show the importance of knowledge of the anisotropy direction in order to interpret the data.