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    A programmable digital metasurface structure designed using ANN technique
    (Taylor and Francis Ltd., 2023) Altıntarla, Gizem; Ünal, Emin; Altıntaş, Olcay; Gençoğlan, Duygu N.; Çolak, Şule; Nazeri, Amir H.; Alkurt, Fatih Özkan
    In this paper, an 8-bit programmable digital metasurface is designed in the operating frequency range from 4 to 7 GHz. A monopole antenna operating at 5 GHz is characterised by using a metasurface structure as the ground plane. Various combinations of the metasurface structure are examined by altering the state of each unit-cell between ‘ON (1)’ and ‘OFF (0)’ in the coding matrix. The purpose of the 8-bit programmable digital metasurface is to control the electromagnetic wave effectively in the frequency range of interest. Dynamically controllable metasurface structure is utilised to change the unit cells’ configurations. In addition, the proposed adjustable metasurface is capable to control the monopole antenna directivity, gain and main lobe magnitude, efficiently. According to various via conditions, different metasurface-based antenna parameters such as return loss (S11), radiation pattern, directivity and surface current distribution are investigated by means of the commercial numerical simulation software, CST microwave studio. Employing the simulation results of the metasurface-based antennas, the artificial neural network (ANN) data set is obtained. 128 activation conditions are trained and tested by Levenberg Marquart learning algorithm. During the ANN procedure, MATLAB is used to obtain accurate results by changing the rate of test and training data set. © 2022 Informa UK Limited, trading as Taylor & Francis Group.
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    Synthesis and characterization of nanoparticles reinforced epoxy based advanced radar absorbing composites
    (Springer, 2021) Tümen, Kutluhan Utku; Kıvrak, Burak; Alkurt, Fatih Özkan; Akyol, Mustafa; Karaaslan, Muharrem; Ekicibil, Ahmet
    In this study, the structural and magnetic properties of NixCo1?xFe2O4 (0.0? x? 1.0) and ZnO nanoparticles synthesized by the sol-gel method were investigated. The microwave property of the composite structures produced from the combination of ZnO and NixCo1?xFe2O4 nanoparticles dispersed in the epoxy matrix property was studied in the X-band frequency range. The crystal structures of NixCo1?xFe2O4 have not been disrupted by Ni substitution, however, the lattice parameters of samples decrease due to the smaller ionic radii of Ni+2 compared to Co+2 ions. The magnetic saturation (Ms) and remanence magnetization (Mr) decreased with an increasing amount of Ni in NixCo1?xFe2O4 structure. According to the microwave absorption properties of samples, the maximum reflection loss (RL) value was found as ?28.10 dB at 10.23 GHz frequency in RAC4 sample. On the other hand, maximum bandwidth was found at 2.95 GHz around ?10 dB for RAC5 sample. All composites exhibit efficient RL in the X-band indicating that they can be used in potential applications in aviation, radar, and defense vehicles. © 2021, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.