Multipath Signal-Selective Metasurface: Passive Time-Varying Interlocking Mechanism to Vary Spatial Impedance for Signals with the Same Frequency

Electromagnetic (EM) multipath interference is difficult to address with passive approaches due to two physical restrictions-the shared frequency of the initial and interfering signals and their variable incident angles. Thus, to address multipath interference, the spatial impedance, i.e., the impedance structured in three-dimensional space, must be adjusted in response to the incident angles of multiple signals with the same frequency, which is impossible with classic linear time-invariant (LTI) systems. We present a design concept for metasurface-based spatial filters to overcome LTI behavior and suppress multipath interference signals using a time-varying interlocking mechanism without any active biasing systems. The proposed filters are comprised of metasurface panels and internally coupled circuit elements including MOSFETs, which permit accepting only the first incoming wave, while adjusting the spatial impedance to reject time-delayed waves from different angles. The proposed concept is numerically and experimentally validated to have a shielding effectiveness of more than 10 dB. This Letter opens a new avenue for passive yet time-varying selective EM metasystems, enabling the adjustment of spatially complicated EM waves and fields even at the same frequency.