[1] The electromagnetic characterization of layered materials is often performed using reflection-only measurements, and through the years several different techniques have been developed to accomplish this both in the laboratory and in situ. It is shown in this paper that the majority of these methods are variations on a single approach, and that closed-form expressions are available to obtain the permittivity and permeability from the measurements. The approach is applicable to free-space (plane wave) measurements, waveguide (non-TEM) measurements, and transmission line (TEM) measurements, and is based on varying the underlying structure of the material stack to obtain independent measurements. Because the formulation is based on specifying the impedances of adjacent regions, the same formula for permittivity and permeability is valid regardless of the complexity of the stack containing the material under test. Examples of several techniques are given using free-space, waveguide, and transmission-line measurements of both dielectric materials and magnetic absorbing materials.Citation: Fenner, R. A., E. J. Rothwell, and L. L. Frasch (2012), A comprehensive analysis of free-space and guided-wave techniques for extracting the permeability and permittivity of materials using reflection-only measurements, Radio Sci., 47, RS1004,

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This work demonstrates the use of genetic algorithms (GA) to transform the traditional free space characterization process into an optimization process. The basis of the process is to compare the measured reflection coefficient to the reflection coefficient computed by the GA. The GA computes the reflection coefficient using candidate solutions of the permittivity and permeability and the Fresnel reflection coefficient equations. The permittivity and permeability that yield the reflection coefficient closest to the measured reflection coefficient is determined to be the best solution. Results using synthetic reflection coefficient data using a Plexiglas sample show accurate extraction of the permittivity with both transverse electric and transverse magnetic polarized plane waves.

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