Evaluation of Permittivity and Thickness Gaging for Anisotropic Dielectric Coatings by the Method of Surface Electromagnetic Waves

Abstract

The widespread use of anisotropic composite dielectric coatings operating in the microwave range in various science-intensive areas has led to the search and selection of effective methods for radio wave nondestructive testing of their electrophysical parameters. The existing approaches based on estimating the reflection and transmission coefficients of electromagnetic waves have low accuracy and reliability in assessing the components of the complex permittivity tensor and the thickness of such coatings and fail to take into account the frequency dispersion of these coatings and their placement on a metal substrate. In this paper, we propose an original method for local evaluation of the components of the complex dielectric permittivity tensor taking into account their frequency dispersion, as well as the thickness of anisotropic dielectric coatings on a metal substrate using radial surface electromagnetic waves of the microwave range. The method is based on solving inverse problems to determine the components of the dielectric permittivity tensor and the thickness of the coatings from the frequency and angular dependences of the field attenuation coefficient of the radial surface electromagnetic wave excited in the sample under study. The numerical and field experiments have shown that for a measurement frequency band of 9–13.5 GHz, the errors in the estimates of anisotropy coefficients are no more than 10% with a confidence level of 0.95. The statistical limit of the resolution of the magnitude off anisotropy in the dielectric permittivity is introduced and substantiated; this makes it possible to evaluate the ability of the method to distinguish two close values of any pair of components of the dielectric constant tensor. Numerical and field experiments have shown that the method can ensure estimation of these values when the difference between them is 0.2–0.3% or less in the frequency range of 9–13.5 GHz.