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.

Time reversal (TR) relies on the reciprocity nature of the wave equation. Waves diverging away from a source can be time reversed and back-propagated to focus back at the source. The transmitting and receiving antenna arrays utilized for TR are collectively termed as the TR mirror (TRM). TR imaging in the microwave regime has shown its promise in nondestructive inspection and target localization. This paper deals with the design of a microwave TRM for the detection of breast tumors. The first part of this paper discusses TR simulations based on a signal processing algorithm, to obtain the tumor location from the total fields. The processed time-reversed fields can be back-propagated in a numerical model to focus the wave at the tumor locations. Simulation results aid in investigating the feasibility and the robustness of the method. The second part of this paper deals with experimental studies for the breast tumor detection, using a pulsed time-domain system and the back-propagation model. The successful detection of single and multiple tumors embedded in a liquid breast tissue-based phantom is shown using the microwave system.

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.

The ability to shrink the physical dimensions of an antenna without significant performance degradation has been of great interest for over half a century. Over the decades, several antenna miniaturization techniques have been proposed, from structural modifications and lumped component loading, to the use of high permittivity/permeability materials, to the more recent applications of metamaterials. In this paper, we provide an overview of antenna miniaturization and a review of various miniaturization techniques with an emphasis on metamaterials. We choose to restrict the scope of our review primarily to antennas for which prototypes have been built and their properties measured. In particular, we concentrate on those metamaterial techniques categorized into the following groups: composite right/left-handed metamaterials, high impedance surfaces, and metamaterial-inspired techniques. Finally, we provide a summary table that allows the reader to compare the performance trade-offs between various miniaturized antennas.

A self-structuring patch antenna (patch SSA) is proposed. It combines the operating principles of the original self-structuring antenna with the desirable properties of a classic microstrip patch antenna. The patch self-structuring antenna has several computer-controlled shorting pins inserted between the patch and the ground plane. By opening and closing these pins, the antenna may be configured to operate at any arbitrary frequency within a very large bandwidth. Additionally, the patch self-structuring antenna may be configured to operate at several simultaneous frequencies that when placed near each other can be used to dramatically expand the instantaneous bandwidth of the antenna. A proof-of-principle study is undertaken both in simulation and by performing measurements on a prototype antenna.