arXiv subjects

Bahman Amrahi

Publications and source records attributed to Bahman Amrahi.

2 recordsLinked to original sources

arXiv2026

Non-Reciprocal Dynamic Metasurface Antenna: Practical Multiport-Network Modeling and Optimization for Multi-User Interference Resilience

Channel reciprocity fundamentally limits full-duplex (FD) base stations due to multi-user co-channel interference. We examine the potential of deploying a non-reciprocal dynamic metasurface antenna (NR-DMA) at the base station to overcome this limitation. Our NR-DMA architecture connects a single circulator to three feed ports of a multi-feed DMA with strong mutual coupling (MC) between its seven feeds and 96 1-bit-programmable meta-elements. We model our system with multiport network theory, using experimentally estimated proxy parameters of a fabricated 19-GHz DMA and the measured circulator response. Our NR-DMA's reconfigurability is captured by a diagonal tunable scattering matrix, showing that non-reciprocal DMAs and RISs need not require a "beyond-diagonal" tunable scattering matrix. We jointly optimize the DMA state, analog feed weights, circulator-port assignment, and circulation direction. Our optimized NR-DMA realizes distinct forward and reverse channel responses. In our interference-limited high-SNR case study, the NR-DMA improves the FD sum rate by about 60% over a reciprocal DMA benchmark. Comparisons with proxy objectives and MC-unaware optimization show that end-to-end FD optimization and MC-aware modeling are both essential.

eess.SP↗

arXiv2025

Strong Mode Coupling via Quasi-Bound States in the Continuum in Bianisotropic Metasurfaces

Electromagnetic mode coupling plays a key role in many resonant effects in nanophotonics. This coupling is also responsible for the appearance of bianisotropy, where electric and magnetic responses become interconnected through the interaction of their respective modes. In this work, we develop a simple and general temporal coupled-mode theory model to describe off-diagonal chiral bianisotropy. Using quasi-bound states in the continuum (q-BICs), we demonstrate how to control the hybridization of modes with opposite symmetries, resulting in Rabi-like splitting between the hybrid states in the regime of strong electromagnetic mode coupling. Beyond revealing the physical origin of the hybrid modes, our model predicts and explains the emergence of dual-band asymmetric reflection and absorption, and how to achieve maximum directional absorption difference. The theoretical predictions are verified by full-wave simulations, showing very good agreement with theory. Furthermore, very strong reciprocal bianisotropy is demonstrated with the use of q-BICs in a deeply subwavelength metasurface in the optical frequency range. Our results provide a clear physical picture of the interaction process between modes, offering a compact theoretical framework for understanding and designing bianisotropic dielectric metasurfaces not only in the traditional regime but also in the strong coupling regime.

physics.optics↗