Wideband Nondestructive Measurement of Complex Permittivity and Permeability Using Coupled Coaxial Probes

A nondestructive measurement system for simultaneous measurement of complex permittivity and complex permeability of planar materials over a wide frequency bandwidth is proposed in this paper. This two-port measurement system consists of two open-ended coaxial probes terminated in flanges that are in contact with the material sheet under test. It measures the reflection from and transmission through the material sheet to extract the electromagnetic properties. Material sheets can be measured without any special preparation, which makes the system more convenient than destructive measurement systems. Theoretical reflection and transmission coefficients are obtained using a rigorous full-wave analysis based on mode-matching technique and Hankel transform. The complex permittivity and permeability of material are found by minimizing the difference between the theoretical and measured reflection and transmission coefficients via Levenberg-Marquardt method. Numerical simulations are performed with finite element solver COMSOL Multiphysics to verify the analytical solution. Experimental setup is designed and the material measurements are performed on a low-loss dielectric and a high-loss magnetic sheet material. Experimental results are compared with those of standard transmission/reflection measurements to validate the accuracy of the proposed system.