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Abstract-A method for predicting the behavior of the permittivity and permeability of an engineered material by examining the measured S-parameters of a material sample is devised, assuming that the sample is lossless and symmetric. The S-parameter conditions under which the material parameters extracted using the Nicolson-Ross-Weir method may be associated with a lossless homogeneous material are described. Also, the relationship between the signs of the real and imaginary parts of the permittivity and permeability are determined, both when the extracted material parameters are real and when they are complex. In particular, the conditions under which metamaterials exhibit double-negative properties may be predicted from the S-parameters of a metamaterial sample. The relationships between material characteristics and the S-parameters should prove useful when synthesizing materials to have certain desired properties. Examples, both from experiment and simulation, demonstrate that the relationships may be used to understand the behavior of several different categories of engineered materials, even when the materials have appreciable loss.

A foldable frequency selective surface (FSS) is introduced that may be tuned by changing the folding state. The FSS comprises periodic elements arranged in an origami-like fashion on a dielectric sheet. By folding and unfolding the FSS, the interaction with the incident field and the mutual interactions between the elements may be altered, resulting in a shift in resonance frequency. A sample design of a tunable FSS folded into a chevron pattern and decorated with cross-shaped copper prints allows a 19% shift of resonant frequency with a change in folding angle of 60 .

The transmission characteristics of a folded surface decorated with a periodic arrangement of split-ring resonators is investigated. The folding pattern has one displacement degree of freedom, allowing motion that can be used to adjust the separation between the rings. When the geometry of the folded surface is varied by mechanical means, the change in spacing between the rings causes a shift in resonance frequency, making the surface mechanically tunable.

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