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Negative impedance converters (NICs) are used to create impedance loads that can effectively cancel the inductive properties of magnetic dipoles, resulting in active metamaterials with increased bandwidth and reduced loss for µ-near-zero (MNZ) and negative-Re(µ) (MNG) media. We demonstrate techniques for analyzing the stability and characterizing the magnetic properties of effective media loaded with NICs. Specifically, we apply the Nyquist criterion to validate the stability of sample active metamaterials. It is shown that the practical NIC-loaded metamaterial may maintain stability and reduce dispersion, albeit with reduced performance as compared to the ideal NIC load.

Active metamaterials loaded with non-Foster inclusions may exhibit broadband and low-loss material properties, as compared to their passive counterparts. However, the study of their noise performance still remains to be explored. In addition to the Johnson-Nyquist noise from lossy conductors, nonlinear materials used for the design of negative impedance converters (NICs) will give rise to noise as well. In this paper, a general analytical model is developed for the prediction of the noise performance of broadband, stable active metamaterials based on NICs. The noise performance is analyzed in relation to stability, and the effective material properties. The techniques developed in this paper can be applied generally to metamaterials for which equivalent circuit models exist, and results are shown demonstrating the power spectral density and the noise figure of the specific case of an active metamaterial consisting of loaded loop arrays. Results are compared to and verified with circuit simulations.

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