Ahmet Teber

In this study, vertically aligned TiO₂ nanowires (NWs) were fabricated on titanium (Ti) foil via thermal oxidation and subsequently coated with zinc oxide (ZnO) using zinc acetate solutions of 25, 50, and 100 mM concentrations. Structural and optoelectronic properties were systematically investigated using SEM, XRD, XPS, PL, UV–Vis, and I–V analyses. SEM results confirmed a progressive ZnO surface coverage, with complete encapsulation observed at 100 mM. EDS analysis revealed a Zn content increase from 0.81 wt.% (25 mM) to 8.43 wt.% (100 mM), accompanied by a decrease in Ti content from 70.78 wt.% to 49.02 wt.%. XRD patterns showed distinct ZnO peaks for coated samples, while XPS confirmed Zn[ ] and Ti[ ] states with minimal interdiffusion. Optical bandgap values increased slightly with ZnO concentration: 3.04 eV (pure TiO₂), 3.06 eV (25 mM), 3.05 eV (50 mM), and 3.11 eV (100 mM), attributed to enhanced crystallinity and heterojunction formation. PL spectra showed increasing green luminescence ([ ]520 nm) with ZnO content, indicating rising defect-related recombination. Electrical measurements showed a sharp rise in photocurrent from 3.67 × 10[ ] A (pure TiO₂) to 4.74 × 10[ ]A (100 mM). Correspondingly, responsivity ([ ]) increased from 0.020 to 2.168 mA/W and detectivity ([ ]*) from 8.5 × 10⁸ to 7.56 × 10⁹ Jones. These results demonstrate that ZnO coating substantially enhances light absorption, charge separation, and carrier transport properties of TiO₂ NWs. The optimized 100 mM ZnO–TiO₂ heterostructure offers high-performance UV photodetection potential for environmental sensing, wearable optoelectronics, and aerospace technologies.

This study aims to develop a flexible and sustainable electromagnetic (EM) wave‐absorbing material by using hemp fabric as a substrate incorporated with multiwalled carbon nanotubes (MWCNTs) and magnetic Ni‐Zn ferrite nanoparticles (NPs). In this context, the objective is to achieve effective EM attenuation across a wide frequency range using a green, lightweight composite to meet the rising demand for ecofriendly shielding in electronic and communication systems. Ni_0.5Zn_0.5Fe₂O₄ and MWCNT composite NPs are uniformly dispersed in a molten paraffin binder and impregnated into hemp fabrics. The magnetic NPs are synthesized via the microwave‐assisted combustion method. The EM parameters of the resulting structure are determined in the X‐band using experimental scattering data and the Nicholson–Ross–Weir method. Absorption performance is evaluated based on varying weight ratios of magnetic NPs and MWCNTs, with an emphasis on impedance matching. The results indicate that combining dielectric and magnetic components significantly enhances absorption. A maximum reflection loss of −72.42 dB and a 3.81 GHz bandwidth (covering over 90.71% of the X‐band) are achieved at 10.08 GHz. Increasing Ni‐Zn content shifts the resonance to higher frequencies. This sustainable, flexible composite shows strong potential for electromagnetic interference shielding, particularly in defense applications requiring radar invisibility.

A metamaterial absorber (MMA) designed for the 5G FR2/mmWave bands (24.25–24.45 and 24.75–25.25 GHz) is simulated with CST Studio Suite and fabricated using laser and wet etching techniques. Absorption measurements are performed using horn antennas in conjunction with a vector network analyzer (VNA). The absorber achieves >95.8% absorption under normal incidence for Mode‐1, while it exceeds 90% for Mode‐2 in the 24.75–25.20 GHz. The simulation results are validated through an electrical equivalent circuit model and experimental data. This absorber presents a promising solution for electromagnetic interference (EMI) reduction and shielding applications. The same structure, scaled from mm to µm without shape alteration, achieved over 90% absorption in the terahertz (THz) region (24–26 THz), particularly in the 24–25.12 THz range. The THz region, known as the “THz gap”, presents challenges due to limited THz sources and detectors. However, technologies such as THz non‐destructive testing (NDT) offer potential in biomedical, communication, and defense applications. From this perspective, the high performance and scalability to µm dimensions without changing the shape of the absorber make it suitable for high‐frequency EM shielding applications. This dual behavior in the GHz and THz regions offers a versatile advantage due to its varied functionality.

In this article, an ultrathin (λ0/14.9), single layer, reflective type polarization converter for either linear-to-circular (LP-to-CP) or linear-to-linear (LP-to-LP) polarization conversion is reported. It has been demonstrated to achieve the LP-to-CP conversion at two separate frequency bands, including 11.52-11.84GHz and 19.83-20.01GHz. The circular polarization type is specified as a right-hand circular polarization (RHCP) for the first band and a left-hand circular polarization (LHCP) for the second band. In both of frequency bands, the metasurface structure reveals highly efficient features. Besides that, the metasurface structure exhibits highly efficient features within 3-dB bandwidths of 10.29-12.58GHz and 19.32-20.50GHz. Crucial parameters of polarization conversion such as ellipticity, axial ratio, and |Eco|/|Ecross| are confirmed to be in good agreement with another one. The metasurface structure's angular stability up to 200 oblique incidence angles makes it useful for beam scanning antennas. CST Microwave Studio program is utilized to carry out extensive simulations. This presented study offers a low cost, relatively high-performance, ultrathin polarization converter capable of linear-to-linear and circular polarization conversion in the X-, Ku-, and K-bands.

The gravitational water vortex power plants (GWVPPs) have established in hydropower systems as a capable approach, generating micro-scale environment friendly electricity. In this system, energy is produced as a result of the interaction of water coming from an inlet canal with the turbine by creating a vortex in circular/conical-shaped structures. This interaction is based on an assumption that the water flow rate in a basin coincides with the tangential velocity on the turbine propeller. In this case, it is essential to investigate numerous geometric design parameters of the cylinder basin and their effects on vortex formation with the help of Computational Fluid Dynamics (CFD). Here, based on the CFD principles, the behaviour of various geometrical parameters on the vortex and tangential velocities in the basin are investigated separately with the help of Ansys Fluent, without using any turbine propeller. For a certain inlet flow velocity and head, different tunable geometric parameters for the gravitational water vortex plant with a cylindrical basin are inlet canal length, basin diameter, basin height and outlet diameter, respectively. The objective is to achieve an improved design configuration concerning factors such as tangential velocity, vortex arrangement, and the optimal placement of turbine propellers within this vortex.

This research describes and assesses a terahertz metamaterial absorber (TMA) with a simple and easy-to-produce structure consisting of gold-silicon (optical)-gold design as a refractive index sensing. Due to the high field limitation in the detection regime, electromagnetic (EM) wave’s absorption reaches 99.40% at a frequency of 3.719 THz, including a significant quality factor (Q-Factor) of 65.77 and a figure of merit, FoM, of 21.49. The TMA has an remarkable sensitivity of 1.215 THz/RIU and can be used as a refractive index sensor (RIS). The proposed metamaterial absorber-based sensor is susceptible to refractive index changes (1.00 to 1.05) in the surrounding medium. For the physical absorption mechanism, the fundamental absorption peak is mainly due to the simultaneous occurrence of electric and magnetic dipole resonances. The proposed absorber has the feature of being an excellent RIS due to its sensing and detection applications.

Since adopting 5G technology, a notable rise in the prevalence of electromagnetic (EM) waves in the environment has become a significant concern. To reduce EM interference, broadband metamaterial absorbers offer an alternative solution for protecting devices in defense, communication, and healthcare applications, unlike their narrowband counterparts. This article presents a numerical investigation of an ultra‐thin, polarization‐insensitive metamaterial absorber (MMA) that uses metasurfaces and provides electromagnetic interference (EMI) reduction, covering the FR2/mmWave licensed N258 and N261 bands with an oblique incidence angle of up to 15 degrees. Comprehensive simulations are performed within the CST Studio Suite S2 2023 to examine the absorber's performance. Under normal incidence, the proposed MMA exhibits a wideband absorbency response exceeding 90% within the frequency range of 24.30–28.12 GHz. Moreover, the physical absorption mechanism is explained with electric and magnetic field distributions, including surface current distributions. Confirmation of the lack of mutual interaction among neighboring unit cells is established through testing with 1 × 2 and 2 × 2 arrays. An equivalent circuit model is also developed to confirm the EM simulation findings. The notable features of the proposed MMA make it an exceptional candidate for EM shielding applications, providing EMI reduction and covering the N258 and N261 bands.

Reflective polarization conversions with a simplistic design of an ultrathin, single-layered, and multi-functional anisotropic metasurface as a polarization converter is utilized for Ku- and K-band applications. The designs with two substrate thicknesses (0.095λ0 and 0.069λ0, respectively) are capable of a cross-polarization converter (CPC) and a linear-to-circular (LTC) polarization conversion. The design with 0.095λ0 thickness achieves a CPC between 17.96 and 26.90GHz with the efficiency of more than 90% and a relative bandwidth of 40% under normal incidence. It maintains angular stability by altering the oblique incidence angles up to 300 with greater than 80% of the PCR in the K-band. Meanwhile, an LTC in two frequency bands, 10.30-10.53GHz and 28.65-29.70GHz, is also numerically demonstrated. The second design with 0.069 λ0 thickness provides a CPC above the PCR value of 87% in the frequency range from 10.46-23.05GHz (covering the entire Ku- and part of the K-band) with angular stability of 40 above the PCR value of 80%. In the meantime, an LTC with relative bandwidth of 75% in the frequency range from 9.53-9.79&24.74-25.27GHz is numerically revealed. These polarization converters exhibit relatively good performances of facile structure and multi-functional properties, which can be useful in Ku- and K-band applications.

A variety of fascinating applications, including 5G communication devices, high-speed data transfer, and large-scale Internet of Things (IoT), make life easier with 5G technology. Despite the 5G’s superior features, the percentage of electromagnetic (EM) waves in the environment execute a significant increase, unpleasantly. Broadband metamaterial absorbers are an appealing alternative to gather these unwanted signals. This study aims to numerically investigate a broadband metamaterial absorber (MMA) in the 5G high-frequency spectral range with the metasurface formed with coupled resistors. In addition, the 24.25-27.5GHz frequency range, one of the high-frequency 5G bands used by selected countries such as the European Union and China, was preferred. The minor aim of this study is that the usage of coupled elements as resistors may have the ability to increase the absorption bandwidth and magnitude. Comprehensive simulations were performed using the finite integration technique (FIT) utilized by the CST Microwave Studio program to investigate the absorber performance and other relevant parameters. The unit cell design is created metal-substrate-metal structures as asymmetric, single-layer, and easy to implement. The absorption responses are investigated according to the oblique incidence angle, polarization angle for TE &TM modes. The suggested MMA provided an absorbency response above 87.6% in the frequency range 24.20-27.30GHz under normal incidence. Moreover, to comprehend the physical mechanism on absorption, the top and bottom surfaces of the absorber's electric field and surface current distributions are assessed. The designed MMA resulting in relatively high performance and polarization insensitive is helpful for electromagnetic interference (EMI) shielding of 5G signals in the FR2/mmWave frequency regime.