Waveform-selective metasurfaces with free-space wave pulses at the same frequency

Time-Domain Filtering of Metasurfaces

“…In addition, these metasurfaces can be potentially exploited for converting a simple sine wave to a different waveform. Although the following study provides numerical simulation results only, similar effects are expected to be obtained experimentally as demonstrated earlier 26 27 28 29 . In realistic measurements, however, there might appear some minor difference in the operating frequencies of metasurfaces due to the presence of solder and parasitic components in diodes, which makes it slightly difficult to analyse the time filtering effects demonstrated below.…”

“…Such a capability of metamaterials and metasurfaces is known to be further extended by introducing nonlinear media or nonlinear circuits as they gave us a flexible tunability to vary electromagnetic properties 22 23 24 25 . Especially, recently developed metasurfaces that consisted of several circuit elements including schottky diodes exhibited new electromagnetic characteristics named waveform selectivity 26 27 28 29 . These waveform-selective metasurfaces allowed us to distinguish different waves even at the same frequency in response to their waveforms or pulse widths.…”

“…Although more details can be seen in past studies 26 28 29 , the fundamental absorbing mechanism is understood in the following manner. As illustrated in Fig.…”

Responses of Waveform-Selective Absorbing Metasurfaces to Oblique Waves at the Same Frequency

“…This new capability to distinguish different waves even at the same frequency was expected to give us another degree of freedom to control electromagnetic waves, thereby leading to development of new kinds of microwave devices and applications such as waveform-selective wireless communications 26 . However, all the past studies were evaluated with only surface waves or free-space waves at a normal angle 23 24 27 , although in reality electromagnetic waves scatter from various structures or boundaries and therefore illuminate such metasurfaces at oblique angles. For this reason we clarify angular dependences of waveform-selective metasurfaces both numerically and experimentally.…”

“…2 ). Compared to our past studies 23 26 27 , we modified and improved our measurement system for conducting oblique incidence measurements in an efficient manner. For example, incoming signals were generated from a vector network analyzer (VNA) (Keysight Technologies N5249A) that, compared to signal generators (which are used for most conventional pulse measurements), significantly reduced the total measurement time but still allowed us to tune the pulse width.…”