Characterization of active metamaterials based on negative impedance converters

Abstract

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.

Broadband matching of nuclear quadrupole resonance detector using non-Foster circuits

“…Stability is an important factor in NIC design, as they can very easily go unstable under certain circumstances. A stability analysis [4,12] based on the location of the poles on the complex s-plane is applied in the analysis of NICs, with a positive real part predicting instability within the NIC. In order to determine the location of the poles of the typical NICs, for example in the Linvill transistor model, the transfer function of the NIC is found as H(s)=Y(s)/X(s), where Y(s) is the Laplace transform of the response of the circuit and X(s) is the Laplace transform of the input.…”

“…If we consider the parasitic effects in a practical model, the procedure can become very complex and it will be difficult to directly find the corresponding roots from the high order polynomials. The Nyquist contour can be used efficiently to determine the stability of a system [12]. The transfer function is expressed as the product of the source impedance Z s (s) and load admittance Y l (s), and when plotted in the complex plane, will encircle the -1 point N times, where N=Z-P, where Z and P are the number of zeros and poles respectively.…”

“…All the impedance poles of an open-circuit stable NIC will be placed in the left half of the plane and is represented by the source impedance, all the admittance poles of a short-circuit stable NIC will be placed in the left half of the plane and is represented by the load admittance. Further details are given in [12].…”

Design of Broadband Non-Foster Circuits Based on Resonant Tunneling Diodes

“…Recent work by Stearns [13], [14] verifies that pole-zero analysis is not suitable for high-order complex network and that the µ-test for unconditional stability [15] is not suitable for NFCs. The frequency domain Nyquist criterion [16] consider the natural frequencies of the complete circuit. Fig.…”

Noise power in active broadband metamaterials

“…Recently the limiting factor associated with active metamaterials, stability, has been investigated by the authors [1,2]. However, the study of their noise performance still remains unexplored.…”