Passive Reconfigurable Intelligent Surfaces with Varying Electromagnetic Response in Accordance with the Pulse Width at the Same Frequency

In recent years, metasurfaces have been broadly and rapidly studied as intelligent reflecting surfaces (IRSs) or reconfigurable intelligent surfaces (RISs) to artificially control electromagnetic waves and signals and facilitate the design of wireless communication environments. These metasurfaces achieve advanced time-varying control through the introduction of active circuit systems including nonlinear circuit components and an external direct-current (DC) source, although such an external energy source is not always available, thereby limiting the applicability of metasurfaces in wireless communications. For this reason, we present a new concept of RISs that are passive configurations but still exhibit variable electromagnetic characteristics in the time domain. Our RISs can change the reflection angle of incident waves depending on the pulse duration of the incident wave. This is achieved by introducing lumped circuit components, including diode bridges, that convert most of the incoming energy to the zero-frequency component to exploit the transient phenomena well known in DC circuits. The proposed concept is numerically tested, in which the reflection angle is changed depending on the incident pulse width. Our study contributes to providing an additional degree of freedom to design wireless communication environments in accordance with the pulse width.