Pseudo‐Waveform‐Selective Metasurfaces and their Limited Performance

Abstract

In recent years, metasurfaces composed of lumped circuit components, including nonlinear Schottky diodes, have been reported to be capable of sensing particular electromagnetic waves even at the same frequency depending on their waveforms, or more specifically, their pulse widths. In this study, analogous waveform-selective phenomena using only linear circuits and linear media are reported. Although such linear metasurfaces are analytically and numerically demonstrated to exhibit variable absorption performance, it cannot strictly be categorized as waveform-selective absorption. It is due to the fact that the waveform-selective responses in the linear metasurfaces originated from the dispersion behaviors of the structures rather than the frequency conversion seen in nonlinear waveform-selective metasurfaces. These linear structures are thus referred to as pseudo-waveform-selective metasurfaces. Additionally, it is shown that the pseudo-waveform-selective metasurfaces have limited performance unless nonlinearity is introduced. These results and findings confirm the advantages of nonlinear waveform-selective metasurfaces, which can be exploited to provide an additional degree of freedom to address existing electromagnetic problems/challenges involving even waves at the same frequency. Artificially engineered subwavelength periodic structures, or socalled metamaterials [1,2] and metasurfaces, [3] are well known to exhibit a wide range of electromagnetic properties, including negative permittivity, [4,5] negative permeability, [6] negative refractive indices, [2] zero refractive indices, [7] asymmetrical responses, [8] and extremely large surface impedances. [3]

Pulse-driven self-reconfigurable meta-antennas

“…The other types of waveform-selective metasurfaces can operate in a similar time period by using larger circuit component values. Theoretically, conventional antennas without waveform-selective metasurfaces may be able to achieve the same performance by using an extremely large quality factor 56 . Realistically, however, this mechanism becomes ineffective due to the presence of even a minor lossy component.…”

Terahertz Pseudo‐Waveform‐Selective Metasurface Absorber Based on a Square‐Patch Structure Loaded with Linear Circuit Components

“…Note that such PWFS absorptions are found to have limited performance unless nonlinearity is introduced. [56] To analyze the CWs selective absorption behavior and initial responses of the linear circuit MSA depicted in Figure 1, an analytical calculation was conducted by varying the pulse width (T pw ) while analyzing the power spectrum of a cosine pulse with an oscillation frequency of 0.18 THz. Figure 4 presents the normalized power THz frequency spectrum for different T pw values of the input cosine pulse signals.…”

“…The obtained curves were generated through the Fourier transform of a continuous cosine wave multiplied by a rectangular pulse extending from t= ÀT pw /2 to T pw /2. The power spectrum P PLS in the frequency range can be expressed by the following equation: [55,56]…”

“…In our calculation method, the absorptance is obtained by sufficiently fine time steps (specifically, 7 ps), which allow us to consider such nonoscillating frequency components as well. Generally, the normalized energy spectral density of the absorbed pulses can be expressed by the equation [56] A…”

Pulse-Driven Self-Reconfigurable Meta-Antennas

“…Theoretically, conventional antennas without waveform-selective metasurfaces may be able to achieve the same performance by using an extremely large quality factor. [56] Realistically, however, this mechanism becomes ineffective due to the presence of even a minor lossy component.…”