Measured complex reflection coefficient of a spatially-extended stratified composite structure, using an open-ended waveguide, can be effectively used to extract key material and geometrical characteristics of any given layer. This is accomplished using a combination of an electromagnetic model and corresponding measurement data. Previously, it was shown that one parameter can be extracted if all others are known. However, practically it is desirable to extract as many pieces of information as possible. To this end the model must be "inverted". However, there is no closed-form solution for the inverse problem, given the mathematical complexity of the forward model. Consequently, we introduce a forward-iterative optimization method to simultaneously extract several pieces of information about the structure. This method defines key unknowns and uses an analytical approach to estimate the reflection coefficient by minimizing a cost-function using conjugate gradient descent (CGD) as optimizer. This paper presents this method along with an experimental result. Information such as thickness and dielectric properties of a layer in a stratified structure is shown to be extracted concurrently.
M. B. Fallahpour et al., "Simultaneous Evaluation of Multiple Key Material Properties of Complex Stratified Structures with Large Spatial Extent," Proceedings of the 38th Annual Review of Progress in Quantitative Nondestructive Evaluation (2011, Burlington, VT), vol. 1430, no. 31, pp. 561-565, American Institute of Physics (AIP), Jul 2012.
The definitive version is available at http://dx.doi.org/10.1063/1.4716277
38th Annual Review of Progress in Quantitative Nondestructive Evaluation (2011: Jul. 17-22, Burlington, VT)
Electrical and Computer Engineering
Keywords and Phrases
Aircraft Radome; And Complex Permittivity Estimation; Conjugate Gradient Descent (CGD); Stratified Composite Structure; Thickness
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