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

In recent years, metasurfaces composed of lumped nonlinear circuits have been reported to exhibit the capability of detecting specific electromagnetic waves, even when the waves are of the same frequency, depending on their respective waveforms or, more precisely, their pulse widths. Herein, three types of metasurface absorbers (MSAs) are presented which are composed of a square-patch structure loaded with linear circuit components, including lumped resistors or resistors in parallel with capacitors/inductors, which can mimic the waveform-selective absorption behavior in the terahertz (THz) region. By judiciously selecting suitable values for the linear circuit components, these MSAs can achieve near-perfect absorption of incident continuous waves or longer pulses while exhibiting reduced absorption of short pulses at the same THz frequency. These linear circuit structures can be referred to as pseudo-waveform-selective MSAs because their waveform-selective absorption characteristics are primarily derived from the dispersion behavior of the resonator structures, as opposed to the frequency conversion commonly observed in nonlinear circuits. These outcomes and discoveries introduce an additional degree of freedom for waveform discrimination in the THz frequency range, potentially enabling a broader range of applications, including but not limited to detection, sensing, and wireless communication.