arXiv subjects

Francisco S. Cuesta

Publications and source records attributed to Francisco S. Cuesta.

4 recordsLinked to original sources

arXiv2026

Wearable metasurfaces for boosting the effective area of mobile-device antennas

Wireless communications increasingly face scenarios with compact user equipments operating in propagation environments where signal blockage, absorption, and device size limitations strongly constrain link performance. Most approaches to wireless-link enhancement focus either on improving base-station antenna systems, for example, through massive MIMO architectures; on engineering the propagation environment using reconfigurable intelligent surfaces and active relays. Here, we propose an alternative user-side strategy for improving wireless links based on wearable metasurfaces that enhance the effective antenna area of compact wireless devices. The proposed passive metasurface is integrated into clothing and engineered to collect the power of electromagnetic waves incident on user's body and route the collected power toward a mobile device in the form of surface waves. This mechanism significantly increases the effective receiving and transmitting area of the device antenna and its gain without external power sources, active control electronics, or additional stand-alone hardware. We implement the concept on a hoodie textile using a scalable screen-printing process with conductive silver ink and demonstrate an approximately tenfold enhancement of the received signal at 26 GHz. This passive approach effectively brings the human body into the communication network by turning clothing into a virtual thin and flexible lens for focusing the incident power on the user equipment.

physics.optics↗

arXiv2026

Efficient Scattering Synthesis for Beyond-Diagonal Non-Local RISs Coupled with Passive Load Networks

Realizing advanced functionalities with high efficiencies via reconfigurable intelligent surfaces (RISs) and reflectarrays requires configurations with strong electromagnetic non-local responses. The traditional approach to achieving strong non-locality has relied on modeling and synthesizing RISs with diagonal load impedance matrices composed of highly dense subwavelength structuring of arrays. In such designs, non-locality is not directly tunable, thereby limiting design flexibility and operational efficiency. This work proposes a rigorous co-simulation-based design and optimization framework for beyond-diagonal RISs with directly controllable non-locality. The co-simulation approach is based on non-local load and coupling networks, integrating electromagnetic antenna characterization with circuit-level modeling of cascaded load networks. The method benefits from additional degrees of freedom by generalizing the conventional diagonal load impedance matrix to a non-diagonal form through a non-local coupling network model. Wide-angle anomalous reflectors based on finite linear and infinite periodic arrays are designed and numerically validated, demonstrating that the proposed non-local loads embedded in realistic cascaded load networks with associated circuitry achieve significantly higher reflection efficiencies than diagonal load matrices at the given element density. Alternatively, for a fixed efficiency target, the required element density can be significantly reduced for efficient synthesis of beyond-diagonal RIS without compromising the performance of wave manipulations.

physics.app-ph↗

arXiv2025

A General Expression for Homogeneous Metasurface Scattering

The general approach in metasurface design is to find the unit-cell properties required to achieve a given functionality. This is usually done by modeling the metasurface as a combination of surface electric and magnetic polarization densities, whose parameters are determined by solving the generalized sheet transition conditions. This is a time consuming task, as the so-called boundary conditions needs to be solved per-case basis, depending on the source polarization, angle of incidence, and intended functionality. Evermore, the task complexity increases as factors such as different media around the metasurface and more than one illumination scenario are taken into account. In this work, we provide a general solution for a uniform metasurface homogenized in terms of susceptibilities. With this model, it is possible to obtain analytical expressions for the specular scattering produced by a metasurface illuminated with arbitrary illumination and angle of incidence. It is expected that the proposed model can ease the analysis and design of metasurfaces, by providing straight-forward expressions which can be simplified by exploiting the unit-cell symmetries.

physics.optics↗

arXiv2024

Angle-Invariant Scattering in Metasurfaces

Metasurfaces are efficient and versatile electromagnetic structures that have already enabled the implementation of a wide range of microwave and photonic wave shaping applications. Despite the extensive research into metasurfaces, a rigorous and comprehensive understanding of their angular dispersion remains vastly under-explored. Here, we use the generalized sheet transition conditions (GSTCs) to model and analyze the angular dispersive properties of metasurfaces. Based on this theoretical framework, we demonstrate that a metasurface may exhibit either partial or complete co- and cross-polarized transmission and reflection coefficients that are angle-invariant, meaning that their amplitude, phase, or both remain unchanged with varying incidence angles. We show that these angle-independent responses exist only when specific conditions, given in terms of the metasurface effective susceptibilities, are met. Using the GSTCs formalism, we derive several of these conditions and illustrate their scattering properties. Among other findings, this analysis reveals that, contrary to common assumptions, nonlocality (spatial dispersion) does not only increase the angular dispersion of a metasurface, but may also be used to achieve complete angle-invariant scattering. Additionally, this work demonstrates that fully efficient extrinsic chirality is possible with a pseudochiral metasurface in a partially angle-invariant fashion. We expect our work to provide a general strategy for eliminating, or at least reducing, angular-dependent scattering responses of metasurfaces, which may prove instrumental for applications that are highly sensitive to the detrimental effects of angular dispersion.

physics.optics↗