Time-varying Elements for Realization of Stable Non-Foster Circuits and Metasurfaces

Funding Information: ACKNOWLEDGEMENT: The authors would like to thank Dr. Xuchen Wang for his help with the numerical simulations done by COMSOL Multiphysics software. This work was supported in part by the Academy of Finland under grant 330260. Publisher Copyright: © 2022 IEEE.It has been recently shown that non-Foster reactances can be realized using time-varying reactive elements. This approach is beneficial in terms of practical realization and stability. Here we show that a time-varying capacitance can be in general used to mimic a static inductance, capacitance, or resistance having arbitrary values. Next, we analyze stability of a simple circuit that contains resistance and emulated negative capacitance and compare it with a circuit with an ideal non-Foster capacitance. Finally, we show an application of our theory to metasurfaces, and, as an example, we indicate that it is possible to create invisible metasurfaces.Peer reviewe