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
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.