Electromagnetically Reconfigurable Fluid Antenna System for Wireless Communications: Design, Modeling, Algorithm, Fabrication, and Experiment

TL;DR

ER-FAS addresses the need for dynamically steerable and pattern-reconfigurable antennas in 5G/6G wireless systems by enabling per-element EM-state reconfiguration through software-controlled fluidics. The authors develop an EM-domain channel model $H_{ m ER} = \gamma {\bf D} {\bf H}_{\rm EM} {\bf B}^T$ and a joint beamforming formulation that optimizes $R = \log_2 \left(1+\frac{P_T |{\bf w}^H {\bf H} {\bf f}|^2}{\sigma^2}\right)$ using a low-complexity alternating/greedy algorithm. Validation is provided via full-wave simulations and hardware measurements (S-parameters, radiation patterns, and SDR BER/power), showing substantial spectral-efficiency gains in far-field and enhanced near-field focusing compared with conventional arrays. Practically, Galinstan-based element and 1×12 array prototypes demonstrate real-time fluidic control and multiple radiation patterns, indicating substantial potential for next-generation wireless networks.

Abstract

This paper presents the concept, design, channel modeling, beamforming algorithm development, prototype fabrication, and experimental measurement of an electromagnetically reconfigurable fluid antenna system (ER-FAS), in which each FAS array element features electromagnetic (EM) reconfigurability. Unlike most existing FAS works that investigate spatial reconfigurability by adjusting the position and/or orientation of array elements, the proposed ER-FAS enables direct control over the EM characteristics of each element, allowing for dynamic radiation pattern reconfigurability. Specifically, a novel ER-FAS architecture leveraging software-controlled fluidics is proposed, and corresponding wireless channel models are established. Based on this ER-FAS channel model, a low-complexity greedy beamforming algorithm is developed to jointly optimize the analog phase shift and the radiation state of each array element. The accuracy of the ER-FAS channel model and the effectiveness of the beamforming algorithm are validated through (i) full-wave EM simulations and (ii) numerical spectral efficiency evaluations. These results confirm that the proposed ER-FAS significantly enhances spectral efficiency in both near-field and far-field scenarios compared to conventional antenna arrays. To further validate this design, we fabricate prototypes for both the ER-FAS element and array, using Galinstan liquid metal alloy, fluid silver paste, and software-controlled fluidic channels. The simulation results are experimentally validated through prototype measurements conducted in an anechoic chamber. Additionally, several indoor communication experiments using a pair of software-defined radios demonstrate the superior received power and bit error rate performance of the ER-FAS prototype.

Figures (21)

• Figure 1: The proposed ER-FAS array element design.
• Figure 2: The operation principle of the proposed ER-FAS array element and radiation patterns at different reconfigurable states.
• Figure 3: Array configuration of the proposed ER-FAS. The feeding network in this work maintains a fixed excitation magnitude while reconfiguring only the phase, though adjusting both is also achievable.
• Figure 4: Simplified hardware block diagram of a single-user MIMO system based on ER-FAS and RF phase shifters.
• Figure 5: The simulated array beampatterns (realized gain in dBi, i.e., relative to an isotropic radiator) for beamforming to $(\theta_\mathrm{az}=-90^\circ,\ \theta_\mathrm{el}=90^\circ)$ using the proposed beamforming algorithm. The conventional antenna stands for the case where each array element's radiation pattern is fixed. Here, we set this fixed radiation pattern as state 2 in Fig \ref{['fig_FAS_Element_Mechanism']}. The same setup applies to Fig. \ref{['fig_RPs_60']}.