Time-Domain Filtering of Metasurfaces

Abstract

In general electromagnetic response of each material to a continuous wave does not vary in time domain if the frequency component remains the same. Recently, it turned out that integrating several circuit elements including schottky diodes with periodically metallised surfaces, or the so-called metasurfaces, leads to selectively absorbing specific types of waveforms or pulse widths even at the same frequency. These waveform-selective metasurfaces effectively showed different absorbing performances for different widths of pulsed sine waves by gradually varying their electromagnetic responses in time domain. Here we study time-filtering effects of such circuit-based metasurfaces illuminated by continuous sine waves. Moreover, we introduce extra circuit elements to these structures to enhance the time-domain control capability. These time-varying properties are expected to give us another degree of freedom to control electromagnetic waves and thus contribute to developing new kinds of electromagnetic applications and technologies, e.g. time-windowing wireless communications and waveform conversion.

Simplified equivalent circuit approach for designing time-domain responses of waveform-selective metasurfaces

“…Waveform-selective absorbing mechanisms have been already reported in our previous studies [23][24][25] but can be briefly understood as below. Firstly, our structures are designed to have a 18 mm periodicity and consist of square conducting patches (perfect electric conductor: PEC; 17×17 mm 2 ), dielectric substrate (1.5-mm-thick Rogers3003 but without loss for the sake of simplicity), and ground plane (FIG.…”

“…Although ordinary metasurfaces have strong frequency dependence and are thus designed to operate at the frequency of interest, circuit-based metasurfaces containing schottky diodes were recently demonstrated to be capable of distinguishing different waves in response not only to the incoming frequency components but also to the waveforms or pulse widths (FIG. 1(a)) [23][24][25][26][27] . Hence, these waveform-selective metasurfaces were expected to give us an additional degree of freedom to control electromagnetic waves even at the same frequency.…”

“…signals at the same frequency, by deploying a proper type of circuit configuration 24,28 . However, although these unique characteristics are easily changed by circuit constants used, none of past studies has yet to clarify how waveform-selective mechanisms are related to the circuit components.…”

“…These time-varying voltages across the inductor and the capacitor are related to absorptance as seen in FIG. 1(d Moreover, combining the two circuit configurations leads to designing more complicated waveform-selective absorbing mechanisms 24 . For example, when the two circuit configurations are connected to each other in parallel as a parallel-type waveform-selective metasurface, both of a short pulse and a continuous wave (CW) are strongly absorbed due to the presence of the capacitor-and inductor-based circuits.…”

“…6 Equations (4) and (7) were used to estimate time constants of these waveform-selective metasurfaces. These analytically derived results were then compared to numerical simulation results that were obtained by a co-simulation method integrating a commercial electromagnetic simulator with a circuit simulator (ANSYS, Electronics Desktop R18.1.0) [23][24][25] . Firstly, a comparison result for an inductor-based waveform-selective metasurface is shown in FIG.…”