Nondestructive measurements of electromagnetic parameters of anisotropic materials using an open-ended waveguide probe system.

摘要

A non-destructive measurement of electromagnetic (EM) properties of anisotropic materials using an open-ended waveguide probe has been conducted. Two different techniques, based on the Hertzian potential method and the transverse field method, are developed to facilitate the investigation of the subject. The technique employing Hertzian potentials is applied to isotropic materials only, however, the technique employing the transverse field method is suitable for both isotropic and anisotropic materials.;A series of experiments have been conducted using the waveguide probe system constructed at MSU electromagnetics laboratory. The experimental results of the probe input admittances, with the probe attached to various isotropic and anisotropic material layers, using an HP 8720B network analyzer are presented. These probe input admittances are then used to determine the complex permittivity inversely by a numerical inverse procedure based on the Newton's iterative method. The inverse results on the EM properties of some known materials are found to be quite satisfactory. The results on the tensor permittivities of some anisotropic materials are found to be reasonable even though their exact values have not been determined before. Finally, an analysis of the effects of material parameters on the input admittance is presented.;When a waveguide probe, which consists of an open-ended waveguide terminated on a flange, is placed against a material layer, two coupled electric field integral equations (EFIE's) for the aperture electric field can be derived by matching the boundary conditions at discontinuity interfaces. These EFIE's can be solved numerically with the Method of Moments (MoM) when the electric field on the waveguide aperture is expressed as a sum of waveguide modes. The reflection coefficient of the incident wave or other relevant quantities of the waveguide probe can be expressed as functions of the EM properties, such as the permittivity, permeability, and conductivity, and the thickness of the material layer. Therefore, the EM parameters of the material layer can be inversely determined if the reflection coefficient of the incident wave is experimentally measured.