Accurate Modeling of Time-Varying Lumped Elements in Space-Time Metasurfaces

The concept of time-varying media provides unique perspective for understanding wave physics and promotes the electromagnetic (EM) devices to incorporate the temporal dimension, leading to time-varying devices. However, this emerging field gives rise to unprecedented challenges in numerical modeling, thereby constraining the potential applications of time-varying devices. In this study, we propose a hybrid method of time-varying lumped element (TVLE) model and the time-domain finite-integration technique (TDFIT) as an efficient approach for accurate analysis of near and far EM fields of the time-varying devices. To validate the accuracy of the proposed algorithm, we conduct numerical simulations and experiments on a space-time metasurface. Excellent agreement between the numerical and measured results demonstrates the superior accuracy of the proposed TVLE-TDFIT method in simulating the far-field patterns, surpassing the widely used analytical approach based on local reflection coefficient in space-time metasurfaces in previous studies. More importantly, our TVLE-TDFIT method enables the efficient simulation of practical time-varying metasurfaces in the near and far field, which was previously unattainable by existing approaches. This work will provide a powerful and versatile tool for the design of cutting-edge time-varying devices.