Recent Advances in Practical Metamaterial Engineering

Abstract

Metamaterials have been used to implement materials with near-zero and negative values of the relative electric permittivity (ɛ), as well as magnetic permeability (μ). These properties enable potentially significant applications, including superlenses, invisibility cloaks, and wideband artificial magnetic conductors. However, it has been proven that passive materials with these properties are necessarily narrow-banded and lossy. Active inclusions can be used to overcome these limitations, albeit at the expense of possible instability and noise issues, and added complexity. We examine a promising possible active implementation: the non-Foster circuit (NFC). Non-Foster circuits are used to create negative impedance loads, and have experienced widespread use for amplifying analog signals in trans-Atlantic telephony cables. There is also a long body of research into their applications for increasing antenna bandwidth. In this presentation, we demonstrate their application to multiple unit-cell metamaterials, and show their potential for possible performance improvements, including increased bandwidth and gain. We also show that maintaining stability is the primary difficulty in designing these complex systems, and has the effect of limiting the range of material properties that may be attained. Additionally, we examine noise and its effect as a mitigating factor in the performance of the metamaterial. Methods are demonstrated for designing robust, stable active metamaterials, and for analysing the noise figure of these structures. We conclude that, although noise and stability limits the bandwidths achievable with these active metamaterials, they still exhibit performances in excess of their passive counterparts, albeit at the expense of DC biasing-voltage requirements.