Abdelghafour Abraray

@it.pt

Instituto de Telecomunicações, Universidade de Aveiro
Instituto de Telecomunicações

Abdel Ghafour Abraray received BSc, MSc degrees from the physics faculty of Abdelmalek Essaadi University. (UAE), Tetuan, Morocco, in 2012 and 2014, respectively. In October 2016, he was accepted for the training period at the University of Coimbra in the framework of the Erasmus Mundus programme, for a period of 6 months. During the years 2017-2018, he was employed as a researcher under the project “Metamaterial superabsorbers for harnessing wireless power” at Instituto de Telecomunicações (IT), Coimbra, Portugal. In 2018-2019, he received a research grant (BI) at IT-Aveiro in the scope of the project “THz communication for beyond 5G Ultra-fast Networks”. Presently, he is a researcher in the project “Programmable Beamforming Metasurfaces” supervised by Dr. Stanislav Maslovski at Instituto de Telecomunicações, Aveiro. He is enrolled into the MAP-Tele Doctoral Programme in Telecommunications at the Departamento de Electrónica, Telecomunicações e Informática (DETI), Universidade do Aveir

EDUCATION

Abraray holds a Master's degree in Electronic and Telecommunication from the physics faculty of Abdelmalek Essaadi University. (UAE), Tetuan, Morocco
Recently he is a PhD student at the University of Aveiro.

RESEARCH, TEACHING, or OTHER INTERESTS

Engineering, Electrical and Electronic Engineering

Scopus Publications

Scholar Citations

Scholar h-index

Scopus Publications

Numerically Optimized Fourier Transform-Based Beamforming Accelerated by Neural Networks
Keivan Kaboutari, Abdelghafour Abraray, and Stanislav Maslovski
MDPI AG
Conventional beamforming methods for reconfigurable reflector antennas assume full control over the amplitude and phase of the reflected field. Here, we develop a novel beamforming methodology for reflecting Programmable Metasurfaces (PMS) with capacitive memory. Although utilizing such fully reactive PMS simplifies antenna design and reduces energy consumption, the PMS reflection magnitude is unity and thus a global optimization of the reflection phases over the PMS unit cells is required in each beamforming scenario. We propose an implementation of such an optimization method rooted in the traditional Fourier transform-based beamforming and evaluate its performance. Additionally, we show that a pair of trained feed-forward neural networks (FFNN) with one input, one hidden, and one output layer can replace time-consuming global optimizations in the case of a PMS comprising 3×10 unit cells. We train the FFNNs on a dataset obtained for typical single- and dual-beam beamforming scenarios. After training, the FFNNs perform requested beamforming tasks within a fraction of second and with about the same accuracy as the original optimization algorithm. The proposed methodology may find applications in future mobile telecommunication systems that require real-time beamforming on low-end hardware. The same beamforming methodology can be also employed in short-range wireless power transfer systems.

Impact of Phase Optimization on the Cascade Channel and System Performance of RIS-Assisted Wireless Networks
Abdelghafour Abraray, Sherif A. Busari, Keivan Kaboutari, Jonathan Rodriguez, and Stanislav I. Maslovski
IEEE
In this work, we investigate the impacts of the Reconfigurable Intelligent Surface (RIS) phases or reflection matrix on the effective cascade (i.e., joint transmitter (TX)-to-RIS and RIS-to-receiver (RX)) channel and on the system performance for RIS-aided wireless networks. Using channel gain, signal-to-noise ratio and spectral efficiency as metrics, we demonstrate that our physical model-based RIS phases employing an optimized Fourier Transform (FT)-based beam-forming algorithm outperforms the cosine similarity (CS) phase algorithm. Unlike the CS algorithm where the RIS phases are deduced from the joint incident and reflected channel vectors, the optimized FT-based phases are blind to the cascade channels. We benchmark our results with random RIS phases as well as the mathematical upper bound. The results show that the FT phases outperform the CS and random phases, and approach the mathematical upper bound performance under diverse system parameters and configurations.

Reflective Metasurface Based on Embroidered Meander Resonators
Abdelghafour Abraray, Marc Martíez-Estrada, Ignacio Gil, Nuno B. Carvalho, and Stanislav I. Maslovski
IEEE
This paper presents a concept of reflecting meta-surface (MS) with a novel unit cell design utilizing embroidered meander resonators. The resonators are formed by a silver-coated nylon thread embroidered on a felt textile substrate and have resonant frequencies around 3 GHz. Numerical simulations and experiments with prototypes have demonstrated that the proposed MS elements have a high and relatively broadband reflection greater than -5 dB in the range 2–4 GHz. Moreover, their resonance frequency can be changed within the same range by modifying the meander arm length. Reflecting MS formed by such elements can be fixed easily on a wall of a house or a tent in urban or rural environments and used as a passive Reflective Intelligent Surface (RIS) to facilitate mobile communications in areas like mountains and deserts. To the best of our knowledge, this paper demonstrates a possibility to use a fully textile MS element for this purpose for the first time.

PIN-diode controlled slot-fed MED antenna for 5G sub-6 GHz applications
Keivan Kaboutari, Amir Siahcheshm, Majid Shokri, Zhale Amiri, Abdelghafour Abraray, Pedro Pinho, Changiz Ghobadi, Javad Nourinia, and Stanislav Maslovski
IEEE
A new reconfigurable Magneto-Electric Dipole (MED) antenna with a slot feed for 5 G sub-6 GHz applications is designed using the “surrogateopt” optimization algorithm. The antenna covers the n78 and n79 frequency bands when a control PIN diode is in “on” and “off” states, respectively. Impedance matching of the proposed MED antenna is achieved by altering the slot width at its center. Full-wave numerical simulations have been conducted to optimize and verify the antenna performance. An equivalent circuit based on Schelkunoff’s theory for dipole antennas and the transmission line theory has been developed to model the antenna input impedance analytically. Both simulation and analytical modeling results show that the proposed reconfigurable MED antenna, with dimensions of $71 \\times 71 \\times 13.63 \\mathrm{~mm}^{3}$, fully covers the n78 and n79 bands and maintains stable gains above 7.6 dBi in these bands.

Design of resonant metasurface absorber using feed-forward neural network
Abdelghafour Abraray, Amit Baghel, and Stanislav Maslovski
Wiley
AbstractIn this work, an ultrathin ( mm) design of a frequency‐selective metamaterial absorber (MTA) is proposed. An absorption of 100% is achieved at the resonant frequency GHz with a fractional bandwidth of 1.45%. The MTA unit cell geometry is parametrized and modeled in a full‐wave electromagnetic simulator. Using a data set generated by varying the absorber unit cell geometry and simulating it in SIMULIA CST Studio Suite, the feed‐forward neural network is able to learn the relationship between the physical structure and its electromagnetic response. The numerical results for the MTA performance have been confirmed by an experiment. An array of 25 MTA elements in a configuration has been fabricated and tested in an anechoic chamber. The simulated and measured results are in a good agreement.

Realization of Programmable Chessboard Mushroom-type Metasurface for Beamforming Applications
A. Abraray, R. A. M. Pereira, K. Kaboutari, and S. Maslovski
IEEE
A reconfigurable microwave reflectarray metasurface (MS) is investigated for beamforming applications. The reflected beam direction is changed by applying external dc voltages, which create a reflection phase gradient on the structure. The studied MS comprises a chessboard-like array of metallic patches placed over a grounded dielectric slab with metallic vias connecting the patches to the controlling lines. Tunability is achieved with nonlinear capacitive loads (varactors) inserted between the corners of the metallic patches. The MS is studied analytically, numerically and experimentally, from which reshaping of the radiation pattern is observed according to the applied control voltages on the MS elements. The beamforming efficiency depends on the size of the MS and the beam width of the source antenna. It is shown that the proposed MS-based reflectarray with just 3-by-10 elements is already sufficient to redirect the beam in different directions.

On Maximum Received Power in Rectenna Structures
A. Abraray, T. R. Fernandes, and S. I. Maslovski
IEEE
The problem of maximization of the power received by an array of coupled compact antennas when connected to a number of loads through an optimal matching network is investigated both analytically and numerically. Theoretical results are obtained for the case of $N$ antennas connected to $M$ loads, and for $N$ antennas connected to a single load. A matching network between the antennas and the following stages, in this case a resistive load, has been designed in order to maximize the power harvested by the input antennas. The matching network is optimized to match the source and load impedances and to reduce the effect of mutual antenna coupling. As a specific example of a compact rectenna element, we consider a pair of coupled res-onant loop antennas with the geometry inspired by the well-known Split-Ring Resonator (SRR). We construct an optimal matching network for this structure based on the developed theory. Such application example featuring high mutual coupling in metamaterial-inspired rectennas is interesting from both theoretical and practical standpoints. To verify the theory, the antennas are simulated in SIMULIA CST Studio Suite. We compare the analytical and numerical results for such structures and make conclusions regarding the applicability and limitations of the developed theoretical framework.

Analytical and numerical modeling of reconfigurable reflecting metasurfaces with capacitive memory
Abdelghafour Abraray, Diogo Nunes, and Stanislav Maslovski
IOP Publishing
Abstract In this article, we develop analytical–numerical models for reconfigurable reflecting metasurfaces (MSs) formed by chessboard-patterned arrays of metallic patches. These patch arrays are loaded with varactor diodes in order to enable surface impedance and reflection phase control. Two types of analytical models are considered. The first model based on the effective medium approach is used to predict the MS reflectivity. The second model is the Bloch wave dispersion model for the same structure understood as a two-dimensional transmission line metamaterial. The latter model is used to study ways to suppress parasitic resonances in finite-size beamforming MSs. We validate the developed analytical models with full-wave numerical simulations. Finally, we propose a design of the MS control network with capacitive memory that allows for independent programming of individual unit cells of the beamforming MS.

Programmable Chessboard Mushroom-Type Metasurface with Memory
A. Abraray and S. Maslovski
IEEE
Here we propose and study a programmable metasurface (PMS) with analog memory that can be used for smart beamforming applications as well as for proactive control of the radio wave propagation environment. The operation of such PMS as a reconfigurable reflect-array is studied analytically and numerically. The PMS comprises a chess-board-like array of metallic patches placed over a dielectric slab with metallic vias connecting the patches to the controlling network. The network includes memory capacitors. The tunability is achieved with varactor loads placed at the corners of the patches. The proposed design has excellent angular stability of the resonant frequency for TE and TM polarizations. Analytical expressions are derived for the PMS surface impedance and reflection coefficient. The analytical results are verified with a number of numerical simulations.

Towards smart beamforming utilizing neural- networked programmable metasurfaces
Abdelghafour Abraray, Antonio Navarro, Nuno Carvalho, and Stanislav Maslovski
IEEE
In this article we outline a beamforming architecture based on the programmable metasurfaces with memory for applications in future device-to-device wireless communications. Programmable metasurfaces have emerged as versatile photonic tools for controlling wave fronts and performing nearly-instantaneous operations on the angular spectrum of propagating electromagnetic waves. The ultimate goal of our research is to implement parts of the signal processing associated with the formation and tracking of the communication beams within such smart, programmable metasurface layers. Here, we discuss the ongoing work towards this goal and present related mathematical models and realization strategies.

Analytical and Numerical Modeling of Reconfigurable Beamforming Metasurfaces
S. Maslovski, A. Abraray, K. Kaboutari, D. Nunes, and A. Navarro
IEEE
Analytical-numerical models of reconfigurable reflecting metasurfaces formed by chessboard-patterned metallic patch arrays with nonlinear capacitive loads are formulated. Two methods are used for the analytical modeling: One based on the effective medium theory and another based on the dispersion equation for the Bloch waves in a two-dimensional transmission line metamaterial. It is shown that the first approach is efficient to predict the reflectivity of a periodic metasurface, while the second approach is efficient to describe the excitation of surface waves on a finite-size structure. The analytical models are validated with numerical simulations. Finite size arrays with varying numbers of unit cells and array geometries are considered. It is observed that the proposed chessboard patterned arrays exhibit excellent angular stability of the resonant frequency independently of the incident wave polarization. Possible methods of beamforming and electronic control in the considered metasurface arrays are discussed.

Beamforming with Intelligent Metasurfaces: Operating Principles and Possible Implementations
Keivan Kaboutari, Abdelghafour Abraray, and Stanislav Maslovski
IEEE
This article discusses a beamforming architecture based on the Programmable Metasurfaces (PMS) for use in future telecommunications. Reflecting beamforming PMS operate by controlling the local reflection phase while omitting the amplitude information. By optimizing the reflection phase distribution using different algorithms, the sidelobe levels are minimized. The acquired phase distributions obtained from the optimization simulations can be used to train a neural network to realize dynamic adaptive beamforming in order to track and control communication beams with predefined characteristics. Here, we discuss the ongoing work towards this goal and present related mathematical models and some simulations results.

Beamforming with Neural-Networked Programmable Metasurfaces
S. Maslovski, A. Abraray, N. Carvalho, and A. Navarro
IEEE
In this presentation, we outline a novel architecture to enable intelligent, reconfigurable multibeam antennas for future device-to-device wireless communications. Two-dimensional metamaterials – metasurfaces – have been proposed for high-throughput microwave/ millimeter and sub-millimeter band communications. Metasurfaces have emerged as versatile photonic tools for controlling wave fronts and performing nearly-instantaneous operations on the angular spectrum of propagating electromagnetic waves. Our aim is to implement the signal processing and control associated with the formation and tracking of the communication beams within the smart, programmable metasurface layers. Offsetting a part of such processing from the silicon to the quasi-optical metasurface layers shall result in reduction of the computational overheads, which is required when dealing with the evergrowing throughput needs for future telecommunications.

A metamaterial-inspired small rectenna for RF energy harvesting based on a 3-way power combiner
Abdel-Ghafour Abraray, Kazi Mohammed Saidul Huq, Shahid Mumtaz, Jonathan Rodriguez, Otman El Mrabet, Abdelkirm Farkhsi, Jean-Marie Floc'h, and Pengbo Si
IEEE
In this paper, we investigate a metamaterial- inspired small rectenna (rectifying antenna) system for microwave energy harvesting and wireless power transfer at 5.8 GHz. We also study the received-power maximization technique using an array of antennas connected to a single load by an optimal RF power combiner. This investigation is done both in simulation and experiment. The power combiner is embedded between the metamaterial- inspired antennas and the load (including rectifier) for maximizing the power, harvested by the input antennas and to deliver it to the load in the most optimal way. Moreover, we design and test proof-of-concept prototypes of the main components of the investigated energy harvesting systems. The similarity between the simulation and the experimental results also confirms our method of investigation.

Design and optimization of compact array rectennas for harvesting wireless power

Conjugate impedance matched metamaterials: Physical modeling and wave interaction effects
Stanislav I. Maslovski, Hugo R. L. Ferreira, Iurii O. Medvedev, Nuno G. B. Brás, Abdelghafour Abraray, Telmo Fernandes, Henrique J. A. Silva, and António L. Topa
IOP Publishing
Conjugate impedance matched metamaterials are shown to be effective traps for electromagnetic waves. Objects made of such materials are able to receive radiation even when it is not directly incident on their surface. Here, we develop methods of physical modeling of such objects and investigate interactions of conjugate impedance matched superabsorbers with passing electromagnetic radiation. We study realizations of such metamaterials with meshes of loaded transmission lines and develop a theory of electromagnetic wave propagation and absorption in such media. Peculiar wave propagation, wave trapping and absorption effects in metamaterial black holes and wormholes are demonstrated. Possible modifications under the goal of optimizing absorption while minimizing complexity of the involved metamaterials are discussed. Conjugate-impedance matched superabsorbers may find applications as efficient harvesters of electromagnetic radiation, and as novel antennas and sensors.

A novel compact CPW OCSRR strucutre for 2.45 GHz rectenna application
M. Bajtaoui, A. Abraray, O. EL Mrabet, Mariem Aznabet, and M. Essaaidi
IEEE
In this paper, a new and compact rectenna is proposed for the application of ISM band at 2.45 GHz using open complementary split ring resonator (OCSRR). The simulated rectifying efficiency and DC voltage were, respectively 57% and 0.9 V when the input power to the rectifying circuit was 0dBm (1mW). The highest efficiency, 62%, was achieved at 2.45 GHz for 3dBm input power and for a charge load 1kΩ.

Design of a 5.8 GHZ rectenna by using metamaterial inspired small antenna
A. Abraray, O. El Mrabet, A. Farkhsi, M. Aznabet, M. Bajtaoui, B. El Jaafari, and J. Floc'h
IEEE
In this paper, we present a new inspired metamaterial rectenna which is designed in the microstrip line structure at 5.8 GHz for the wireless transmission of microwave power. The proposed rectenna achieves RF-to-DC conversion efficiency of 52% and a DC voltage of 0.8 V when the received RF power is 1 mW at 5.8 GHz. The feasibility of this concept is presented through full-wave simulations. These simulations results will be updated at the conference with measurement results.

RECENT SCHOLAR PUBLICATIONS

Impact of Phase Optimization on the Cascade Channel and System Performance of RIS-Assisted Wireless Networks
A Abraray, SA Busari, K Kaboutari, J Rodriguez, SI Maslovski
2024 International Microwave and Antenna Symposium (IMAS), 1-4 2024

Reflective metasurface based on embroidered meander resonators
A Abraray, M Martez-Estrada, I Gi, NB Carvalho, SI Maslovski
2024 International Microwave and Antenna Symposium (IMAS), 1-4 2024

PIN-diode controlled slot-fed MED antenna for 5G sub-6 GHz applications
K Kaboutari, A Siahcheshm, M Shokri, Z Amiri, A Abraray, P Pinho, ...
2024 international conference on electromagnetics in advanced applications 2024

Numerically Optimized Fourier Transform-Based Beamforming Accelerated by Neural Networks
K Kaboutari, A Abraray, S Maslovski
Applied Sciences 14 (7), 2866 2024

Design of resonant metasurface absorber using feed‐forward neural network
A Abraray, A Baghel, S Maslovski
Microwave and Optical Technology Letters 66 (1), e33977 2024

Realization of programmable chessboard mushroom-type metasurface for beamforming applications
A Abraray, RAM Pereira, K Kaboutari, S Maslovski
2023 Photonics & Electromagnetics Research Symposium (PIERS), 1909-1913 2023

On Maximum Received Power in Rectenna Structures
A Abraray, TR Fernandes, SI Maslovski
2023 Photonics & Electromagnetics Research Symposium (PIERS), 889-896 2023

Analytical and numerical modeling of reconfigurable reflecting metasurfaces with capacitive memory
A Abraray, D Nunes, S Maslovski
New Journal of Physics 24 (7), 075003 2022

Chessboard Mushroom-Type Metasurface for Beamforming Applications
A Abraray, R Pereira, K Kaboutari, S Maslovski
arXiv preprint arXiv:2205.14671 2022

Analytical and numerical modeling of reconfigurable beamforming metasurfaces
S Maslovski, A Abraray, K Kaboutari, D Nunes, A Navarro
2021 Photonics & Electromagnetics Research Symposium (PIERS), 2637-2647 2021

Beamforming with Intelligent Metasurfaces: Operating Principles and Possible Implementations
K Kaboutari, A Abraray, S Maslovski
2021 International Conference on Electrical Engineering and Photonics 2021

Programmable chessboard Mushroom-type metasurface with memory
A Abraray, S Maslovski
2021 Fifteenth International Congress on Artificial Materials for Novel Wave 2021

Towards smart beamforming utilizing neural-networked programmable metasurfaces
A Abraray, A Navarro, N Carvalho, S Maslovski
2021 Telecoms Conference (ConfTELE), 1-6 2021

Beamforming with Neural-Networked Programmable Metasurfaces
S Maslovski, A Abraray, N Carvalho, A Navarro
2020 Fourteenth International Congress on Artificial Materials for Novel 2020

A metamaterial-inspired small rectenna for RF energy harvesting based on a 3-way power combiner
AG Abraray, KMS Huq, S Mumtaz, J Rodriguez, O El Mrabet, A Farkhsi, ...
2019 IEEE Global Communications Conference (GLOBECOM), 1-6 2019

Design and optimization of compact array rectennas for harvesting wireless power
AG Abraray, TR Fernandes, SI Maslovski
Loughborough Antennas & Propagation Conference 2018 (LAPC 2018), 64 2018

Conjugate impedance matched metamaterials: Physical modeling and wave interaction effects
SI Maslovski, HRL Ferreira, IO Medvedev, NGB Brs, A Abraray, ...
Journal of Physics: Conference Series 1092 (1), 012084 2018

A novel compact CPW OCSRR strucutre for 2.45 GHz rectenna application
M Bajtaoui, A Abraray, OEL Mrabet, M Aznabet, M Essaaidi
2016 International Renewable and Sustainable Energy Conference (IRSEC), 979-982 2016

Design of a 5.8 GHZ rectenna by using metamaterial inspired small antenna
A Abraray, O El Mrabet, A Farkhsi, M Aznabet, M Bajtaoui, B El Jaafari, ...
2016 5th International Conference on Multimedia Computing and Systems (ICMCS 2016

MOST CITED SCHOLAR PUBLICATIONS

Analytical and numerical modeling of reconfigurable reflecting metasurfaces with capacitive memory
A Abraray, D Nunes, S Maslovski
New Journal of Physics 24 (7), 075003 2022
Citations: 6

Towards smart beamforming utilizing neural-networked programmable metasurfaces
A Abraray, A Navarro, N Carvalho, S Maslovski
2021 Telecoms Conference (ConfTELE), 1-6 2021
Citations: 6

Design and optimization of compact array rectennas for harvesting wireless power
AG Abraray, TR Fernandes, SI Maslovski
Loughborough Antennas & Propagation Conference 2018 (LAPC 2018), 64 2018
Citations: 5

Beamforming with Neural-Networked Programmable Metasurfaces
S Maslovski, A Abraray, N Carvalho, A Navarro
2020 Fourteenth International Congress on Artificial Materials for Novel 2020
Citations: 3

Programmable chessboard Mushroom-type metasurface with memory
A Abraray, S Maslovski
2021 Fifteenth International Congress on Artificial Materials for Novel Wave 2021
Citations: 2

Numerically Optimized Fourier Transform-Based Beamforming Accelerated by Neural Networks
K Kaboutari, A Abraray, S Maslovski
Applied Sciences 14 (7), 2866 2024
Citations: 1

Design of resonant metasurface absorber using feed‐forward neural network
A Abraray, A Baghel, S Maslovski
Microwave and Optical Technology Letters 66 (1), e33977 2024
Citations: 1