Measurement of the equivalent complex permittivity of electromagnetic structural materials without prior thickness

Electromagnetic structural materials exhibit significant sensitivity to the polarization state and incidence angle of electromagnetic waves. The equivalent complex permittivity is the core parameter that describes the dielectric properties of electromagnetic structural materials. Therefore, accurate characterization of their equivalent complex permittivity is essential for establishing electromagnetic models and guiding the design of functional devices. This paper proposes a broadband inversion method based solely on reflection measurements at different incident polarizations and incident angles. By establishing a set of adaptive equations for multi-reflection measurement states under oblique incidence, the proposed method directly resolves the equivalent complex permittivity without requiring prior knowledge of the sample thickness and iterative phase unwrapping, and obtains broadband measurement results in a single measurement. The simulation and experimental results show that this method has good testing consistency and accuracy. This study provides a high-precision, low-cost and efficient testing solution for dielectric property evaluation of electromagnetic structural materials. It can simplify the complex modeling design of electromagnetic structural materials into an equivalent single-layer material design, providing a reference value for rapid analysis of the scattering characteristics of complex structures.