Design and Analysis of an Electronically Tunable Magnet-Free Non-Reciprocal Metamaterial

In this communication, we develop and experimentally test a fully tunable magnet-free, non-reciprocal, split-ring resonator-based metamaterial. Non-reciprocity in the material response is introduced by bridging the split-ring gap with a biased field-effect transistor (FET) transistor, which allows the non-reciprocity to be tuned with respect to gate–source and drain–source bias conditions. As a measure of non-reciprocity, we consider the Faraday rotation of a normally incident linearly polarized planewave, which is a function of the co-polarized and cross-polarized
$S$
-parameters associated with two horn antennas that transmit and receive the wave. Faraday rotation is calculated with respect to the operating frequency of the horn antennas and manually measured with respect to drain–source current at the resonant frequency. Interestingly, we find a linear relationship between Faraday rotation and drain–source current at the resonance.