Frequency-Selective Surface Based on Negative-Group-Delay Bismuth-Mica Medium

Negative group delay may be observed in dispersive media with anomalous dispersion in a certain frequency range. The fact that an outgoing wave packet precedes an incoming one does not violate the causality principle but is only a consequence of a waveform reshaping. This effect is observed in media such as photonic crystals, hyperbolic and epsilon-near-zero metamaterials, undersized waveguides, subwavelength apertures, side-by-side prisms, and resonant circuits at various frequencies. The current work is devoted to the design of a simple negative-group-delay medium with tunable properties in the THz frequency range. This medium consists of a bismuth-based frequency-selective surface on a dielectric substrate and may be tuned both statically and dynamically. While a geometry variation defines a main form of an effective permittivity dispersion and group delay/group velocity spectra, an external voltage allows one to adjust them with high precision. For the configuration proposed in this work, all frequency regions with noticeable change in group delay/group velocity lie within atmospheric transparency windows, which are to be used in 6G communications. This medium may be applied to THz photonics for a tunable phase-shift compensation, dispersion management in systems of THz signal modulation, and for encoding in next-generation wireless communication systems.

Automated summary

Negative group delay can occur in dispersive media within a specific frequency range, but it does not violate causality and is a result of waveform reshaping. This effect can be observed in various media such as photonic crystals, metamaterials, waveguides, apertures, prisms, and circuits at different frequencies. The current study focuses on designing a simple, tunable negative-group-delay medium for use in the THz frequency range. The medium consists of a bismuth-based frequency-selective surface on a dielectric substrate, and its properties can be adjusted both statically and dynamically. This medium has applications in THz photonics for phase-shift compensation, dispersion management in THz signal modulation systems, and encoding in next-generation wireless communication systems.