İlgi alanları

Sürdürülebilir Kalkınma Amaçları

• 2
• 1

• MakaleYalnız künye2025Scopus SJRQ4/r/bayburt/11530
  Tunable optoelectronic performance of ZnO-Coated TiO2 nanowires for enhanced UV photodetection

  Sarac, M.F.; Solakyildirim, T.; Teber, A.

  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 Zn2+ and Ti4+ 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 × 10−6 A (pure TiO2) to 4.74 × 10−4 A (100 mM). Correspondingly, responsivity (R) increased from 0.020 to 2.168 mA/W and detectivity (D*) from 8.5 × 108to 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.

  AtıfOpenAlex1

  İncele
• MakaleAçık Erişim2025Scopus SJRQ2/r/bayburt/11246
  High-Performance Microwave-Absorbing Hemp Textile: Ni-Zn Ferrite and Multiwalled Carbon Nanotubes-Infused Nanocomposite for X-Band Electromagnetic Interference Shielding

  Teber, Pembe; Teber, Ahmet; Karakaş, İbrahim Hakkı

  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. Ni0.5Zn0.5Fe2O4 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.

  AtıfScopus1·WoS1·OpenAlex1

  İncele
• MakaleAçık Erişim2025Scopus SJRQ1/r/bayburt/11242
  Design, Simulation, and Fabrication of High-Performance Metamaterial Absorber for EMI Mitigation and THz NDT/Imaging Applications: A Shape-Preserved GHz-to-THz Transition Approach

  Teber, Ahmet

  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.

  AtıfScopus4·WoS4·OpenAlex3

  İncele
• MakaleAçık Erişim2025Scopus SJRQ3/r/bayburt/11081
  Tailoring the optoelectronic properties of ZnO nanowires via TiO2 coating

  Sarac, Mehmet Fahri; Mert, Merve; Solakyildirim, Tuba; Teber, Ahmet

  The photosensing properties of TiO2/ZnO nanowires (NWs) were investigated by sequential deposition using thermal oxidation and sol–gel. It was found that TiO2/ZnO NWs with 5 mM concentration exhibit a higher aspect ratio compared to the 10 mM and 25 mM TiO2/ZnO NWs. The surface-to-volume ratio directly influences the photoluminescence (PL) intensity and electrical properties of the ZnO NWs. XPS confirmed the presence of TiO2 on the surface, while EDS detected titanium, with its concentration increasing as the TiO2 concentration rises. The photosensing performance of ZnO has been significantly improved by modifying it with TiO2. However, determining the optimum concentration is a critical factor in performance improvement. The findings show that high TiO2 concentrations improve surface properties, but excessive coating may limit carrier mobility. Photosensitivity has been increased at lower TiO2 concentration due to a higher surface-to-volume ratio (SVR) and, as a result, higher surface photoactivity. The 25 mM TiO2/ZnO NW array stands out in optimal detectability and photoresponsivity due to the reduced resistance caused by the increased Ti concentration on the surface. The 25 mM TiO2/ZnO NWs achieved the highest photoresponsivity (717 mA/W) and specific detectivity (1.48 × 101° Jones), while the 5 mM TiO2/ZnO NWs exhibited exceptional photosensitivity (320.11%), making them ideal for UV detection. The samples at varying concentrations show promise in photosensitivity, detectability, and photoresponsivity, making them suitable for environmental sensors, UV detectors, and other optoelectronic applications.

  AtıfOpenAlex1

  İncele
• MakaleAçık Erişim2024/r/bayburt/16379
  Refractive Index Sensor Based on Terahertz Metamaterial Absorber with High Sensitivity and Quality Factor for Sensing Applications

  Teber, Ahmet

  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.

  AtıfOpenAlex3

  İncele
• MakaleAçık Erişim2024/r/bayburt/13104
  Ultra-thin Polarization Converter Using Single Layer Metasurface for X-, Ku-, and K-Band Applications

  Arslan Madak, Seher Şeyma; Teber, Ahmet; Topkaya, Ramazan

  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.

  AtıfScopus2

  İncele
• MakaleAçık Erişim2024/r/bayburt/12945
  Polarization Insensitive and Thin Metamaterial Absorber Performed in High-Frequency 5G Bands

  Arslan Madak, Seher Şeyma; Teber, Ahmet; Topkaya, Ramazan

  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.

  AtıfScopus3·TR Dizin1

  İncele
• BildiriAçık Erişim2024/r/bayburt/12924
  Tangential velocity and water vortex structure behaviour based on cylindrical-shaped basin's design parameters for gravitational vortex power plants

  Teber, Ahmet

  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.

  • 
  AtıfScopus1

  İncele
• MakaleAçık Erişim2024Scopus SJRQ2/r/bayburt/12884
  A Dual-Band Terahertz Metamaterial Absorber Using an All-Metal Aluminum Hexagonal Metasurface Structure for Sensing of Cancerous Cells

  Teber, Ahmet

  This article proposes a dual-band terahertz metamaterial absorber (TMA) where all components of the designed structure are made of aluminum (optical) material. Unlike the metal-dielectric-metal structures typically found in the literature, the proposed structure has a lightweight material that does not contain a sandwich structure. Thus, the structure greatly simplifies the production process and reduces the cost. The results of electromagnetic and equivalent circuit simulations are compared based on the S11 parameters (in dB), resulting in good agreement of findings by CST and ADS, respectively. The proposed TMA operates in dual frequency bands at 1.902 THz (f1) and 1.976 THz (f2), with strong absorption of 98.17% and 99.05%, respectively. The quality factors (Q-factors) corresponding to these resonant frequencies are 240.15, (f1) and 181.61, (f2). When the refractive index (RI) of the medium surrounding the TMA varies, the absorption peaks shift accordingly. The detection properties of the proposed TMA are examined as the RI of the surrounding medium is varied primarily between 1.34 and 1.39 with an increase of 0.01 for biomedical applications. The corresponding sensitivities of two resonance peaks are 0.794 THz/RIU and 0.971 THz/RIU, respectively. Since many samples, such as human blood, basal/breast/cervical cells, and cancerous cells, are found in this RI range, the proposed TMA sensor can be used as a viable biosensor in the identification of biological samples for real-world applications. Graphical Abstract: (Figure presented.)

  AtıfScopus36·WoS31·OpenAlex37

  İncele
• MakaleAçık Erişim2024Scopus SJRQ2/r/bayburt/11858
  Niobium modification on dielectric, magnetic and structural features of nanocrystalline Ni–Co ferrites

  Teber, Ahmet; Sarac, Mehmet Fahri

  In this study, we will investigate the structural, characteristic, dielectric and magnetic features of Co0.5Ni0.5Nb xFe2–xO4 (0.0 ≤ x (with 0.2 increments) ≤ 1.0) nanoparticles, which are prepared via the hydrothermal approach. M-type hexagonal crystal structures are confirmed through XRD, FT-IR, SEM-EDS, TEM-SAED and VSM. Also, we have reported the investigations on dielectric properties and ac conductivity. Based on XRD measurements, it is concluded that all samples have M-type hexagonal crystal structure with nanocrystals ranging from 60 to 97 nm. The diffraction patterns obtained matched well with the calculated patterns from Rietveld analysis. Moreover, from the morphological analysis, it was observed that the small spherical structures of Ni–Co ferrite particles transformed into quadrilateral structures with increasing Nb concentration. The results of the FT-IR study show that the hexaferrite structure is formed as predicted because the expected range of absorption bands is present. According to VSM, Nb-substituted Ni–Co ferrite nanostructures reveal a relatively soft ferromagnetic property. Increasing the concentration of Nb tends to increase the coercive field (H c) variation. The dielectric factors and ac conductivity were measured in the frequency range of 0.1–10 MHz. The reduction in dielectric factors and tangent losses at low frequencies can be elucidated by both deformation and relaxation polarization mechanisms. Another observation is that ac conductivity is amplified with the applied frequency. In this sense, the electron and hole hopping phenomenon can explain the conduction mechanism.

  İncele