Solutions of fields inside a slab of a generally lossy dielectric medium backed by a conducting plate, placed outside a waveguide-fed rectangular aperture, are evoked in the application to the microwave nondestructive thickness measurement of such dielectric slabs. Upon construction of the waveguide terminating admittance expression from its variational form, an inverse problem is then solved to extract the slab thickness from the conductance and susceptance in a recursive manner. A comparison between the experimental and theoretical results showed that the significance of higher order modes is minimal; hence, the dominant mode assumption is, in general, valid to describe the aperture field distribution. The validity of this assumption has led to the construction of a simple integral solution which is fast converging for generally lossy dielectric slabs, and may easily be implemented for realtime applications. Experiments were conducted to verify the theoretical findings. Good agreement was obtained between the theoretical and experimental results. Multiple thicknesses of two different dielectric samples were estimated in this way.


Electrical and Computer Engineering

Keywords and Phrases

Aperture Field Distribution; Conducting Plate; Dielectric Slabs; Inverse Problems; Lossy Dielectric Medium; Lossy Dielectric Slabs; Microwave Measurement; Microwave Nondestructive Thickness Measurement; Nondestructive Thickness Measurement; Real-Time Applications; Rectangular Waveguides; Recursive Manner; Thickness Measurement; Variation Detection; Waveguide-Fed Rectangular Aperture; Composite Testing And Evaluation; Electromagnetic Formulation-Probe Development And Antennas

International Standard Serial Number (ISSN)


Document Type

Article - Journal

Document Version

Final Version

File Type





© 1993 Institute of Electrical and Electronics Engineers (IEEE), All rights reserved.

Publication Date

01 Feb 1993