Susceptibility Invariance and Duality-Matching Condition for Perpendicular-Motion Metasurface

Time-varying metasurfaces have recently emerged as a promising platform to observe exotic wave behaviors in space-time systems. In this paper, it theoretically reveals invariant susceptibility parameters for perpendicular-moving metasurface. Duality-matching condition is derived by utilizing generalized sheet transition conditions (GSTCs) combined with Lorentz transformation (LT). A metasurface that satisfies the duality-matching condition can hold its susceptibility parameters when it moves perpendicularly toward the sources. The moving-invariant behavior is further discussed in time-varying media and additional reflection is found to be inevitable if the constitutive parameters is discrete in time.