Sürdürülebilir Kalkınma Amaçları

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• MakaleAçık Erişim2026Scopus SJRQ1/r/bayburt/11553
  Permittivity Extraction of Electrically Thin Samples by Reflection-Only Free-Space Measurements

  Hasar, Ugur C.; Xue, Bing; Ozturk, Hamdullah; Kaya, Yunus; Ozturk, Gokhan

  A permittivity extraction procedure is devised for electrically thin samples from reflection-only free-space measurements. Unlike previous studies, this procedure relies on sample-back metal termination measurements especially useful for thinner samples. An objective function independent of antenna transmission characteristics and reference plane position is derived. Minimum and maximum thickness and permittivity values for which our method is applicable are also examined. Free-space measurements at X-band (8.2-12.4 GHz) of a Rogers 4350B sample (approx 1.52 mm) and a FR4 sample (1.60 mm) were performed to validate our method with a dielectric constant less than 5% variation.

  AtıfScopus1·WoS1

  İncele
• MakaleAçık Erişim2026Scopus SJRQ1/r/bayburt/11526
  Determination of complex permittivity of a thin low-loss dielectric sample using state-space approach from waveguide measurements

  Hasar, Ugur C.; Ali, Husain; Kaya, Yunus

  An extraction procedure is proposed for relative complex permittivity () determination of thin low-loss samples positioned/deposited on a supporting substrate material using waveguide non-resonant microwave measurements. Its substrate thickness and sample thickness independence makes it unique extraction method in comparison with the available retrieval methods which are free from either substrate thickness information only or sample thickness information only. Its theoretical model is constructed on the state-transition matrix and state vector through which the link between and measured scattering (S-) parameters is established. Compared with previous works in the literature, a closed form (explicit) expression of is derived for a two-layer (sample on a substrate material) composite structure, thereby eliminating any numerical analysis or tool. Numerical analyses are implemented for validation of the proposed method as well as assessing the effect of noise and any possible air gap between the sample and its substrate. X-band ( GHz) waveguide measurements of a thinner (around 1.00 mm) polyvinyl chloride (PVC) for different measurement scenarios and measurements of a thin zinc oxide film (m) were performed to evaluate the performance of the proposed extraction method against other similar methods in the literature. Our method can find applications for characterization of thin-film, radar-absorbent material coatings, anti-corrosive paints, or thermal barrier coatings where sample thickness (and substrate thickness) can vary from one sample to another from the same batch.

  İncele
• MakaleYalnız künye2026Scopus SJRQ1/r/bayburt/11397
  Reference-Invariant Permittivity Determination of Low-Loss Solid Dielectric Samples Using Spectral Free-Space Measurements Without Prior Thickness

  Hasar, Ugur C.; Ali, Husain; Kaya, Yunus

  An extraction method has been proposed for relative permittivity determination εrs of low-loss solid dielectric samples using free-space measurements. It relies on a reference-plane invariant expression with no thickness information a priori, making resistant to conventional free-space measurement errors which may arise from improper information of sample position and thickness. In addition, the method constructed by the state transition matrix (STM) uses closed-form expressions – a feature distinguishes our method from previous STM-based extraction methods requiring a numerical tool or optimization procedure. Furthermore, provided that the sample thickness L is evaluated, as a by-product, first using the derived closed-form objective function away from any thickness-resonance region, the proposed method then determines εrs and L free from thickness-resonance effect, which otherwise can introduce ripples around or at the thickness-resonance frequency. Numerical analysis is performed to validate and assess the performance of our method. Free-space measurements at X-band of two low-loss samples with substantial thickness are performed for validation and accuracy comparison of our method against other similar methods.

  İncele
• MakaleAçık Erişim2026Scopus SJRQ1/r/bayburt/11188
  Permittivity extraction of sandy soils through uncalibrated and thickness-independent meniscus-free measurements using a hollow coaxial line

  Hasar, Ugur C.; Korkmaz, Huseyin; Kaya, Yunus

  Measurement techniques for accurate moisture level determination of various soil conditions are becoming popular in recent studies. Microwave-driven techniques, as positioned into indirect methods, could be tailored for precise and real-time detection of soil moisture. However, improper implementation of calibration techniques or usage of imperfect calibration standards required for precise measurements by these techniques presents a challenging limitation for their widespread usage. Besides, meniscus formation on top of soil samples with a sufficient moisture level could adversely influence the performance of these techniques. In this study, we present a microwave extraction method for eliminating the requirement of a formal calibration procedure and additionally removing the effect of meniscus on measurements through relative measurements of sandy soil samples while maintaining accurate permittivity extraction with no information of sample thickness. To achieve our goal, a mathematical framework unifying wave-cascading matrix and state-transition matrix presentations is proposed for permittivity determination from three measurement configurations (empty line, the (sandy) soil sample sandwiched between two identical plugs, and a shifted version of this plug-sample-plug configuration) and their inverses implemented by port switching operation. The proposed method is first validated by permittivity measurements of two liquid samples (distilled water and methanol). Then, permittivity measurements of two sandy soil samples (having more than 90% sand content) were conducted using Type-N-to-EIA 1-5/8” coaxial lines (with no universal calibration standard) over 0.05 GHz–3.0 GHz. From these measurements, it is noted that our meniscus-free method determines permittivity with a maximum absolute difference of 3.4% (evaluated from five independent measurements) while another similar method, suffering from meniscus presence, extracts permittivity with a maximum absolute difference of 4.0%. This indicates a clear advantage of our method for measurements of sandy soil samples having meniscus formation. We then utilized to construct a calibration curve, compared with other calibration curves using by other methods, allowing prediction of moisture volume content () of the tested sandy soil samples from measured permittivity data whose conformity analysis implemented by the three-pole Debye model and the Mironov-Fomin model. It is observed that this calibration curve could be utilized to predict within margin from measured permittivity data.

  İncele
• MakaleAçık Erişim2025Scopus SJRQ1/r/bayburt/10822
  Quantification of Honey Adulteration Using a Planar Microstrip Metamaterial-Motivated Sensor and Software-Defined Radio

  Cem Hasar, Ugur; Hasar, Hafize; Kaya, Yunus; Ozturk, Hamdullah; Korkmaz, Huseyin; Kosunalp, Selahattin; Iliev, Teodor; Tariqul Islam, Mohammad; Nayyeri, Vahid; Mustafa Ramahi, Omar

  This work presents the application of a planar microstrip metamaterial (MM)-motivated sensor in the form of a split-ring resonator (SRR) for the detection and quantification of water adulteration in honey samples. The proposed sensor utilizes inexpensive software-defined radio (SDR) measurements, offering a cost-effective solution. Unlike previous MM sensors employing SRR configuration, our proposed MM-motivated sensor is integrated with a microstrip feedline and an additional vertical bar, enhancing its sensing capability. To enable accurate measurements, a simple calibration procedure based on baseline normalization is implemented, allowing for amplitude-only transmission measurements (|S-21|) using the SDR. A special sample holder was designed to increase the repeatability of measurements. We separately employ two postprocessing techniques, namely, the rolling average (RA) approach and the Savitzky-Golay (SG) filter, to effectively eliminate ripples in the measured |S-21| data obtained from the SDR. For validation and evaluation of the proposed sensor and postprocessing techniques, measurements of flower honey samples with water adulteration levels (delta ) up to 10% (mass-to-mass basis) were also performed using a vector network analyzer (VNA). The resonance frequency of |S21| is utilized as the basis for analysis. We establish a metric function (linear function) that correlates the shift in resonance frequency with delta. It is observed that this function fits to measured resonance frequency values with an R(2 )value greater than 0.96 for both postprocessing techniques with or without the sample holder. By inverting this function, we can predict delta with considerable accuracy for a given resonance frequency by using another linear function. It is observed that percentage variations between predicted and measured delta values are between 1.54% and 6.46% for testing samples with delta = 5% and delta = 7%.

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  AtıfScopus5·WoS2·OpenAlex5

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• MakaleAçık Erişim2025Scopus SJRQ1/r/bayburt/12776
  Broadband Multilayer Absorber Design Using Double-Stage Cognitive Seeker Optimization Algorithm

  Hasar, Ugur Cem; Kaya, Yunus; Korkmaz, Huseyin; Iliev, Teodor

  In this paper, a double-stage cognitive seeker optimization (DSC-SO) algorithm is developed for evaluating optimum design parameters of broadband microwave absorbers. The algorithm not only gives freedom of selecting different number of layers and optimizing the order of layers and their thickness in different stages (double-stage) but also utilizes a cognitive search to improve the optimization. Contributions of the cognitive search and the two stages of our algorithm are first examined to show its efficiency. Then, its performance has been evaluated for two different optimization problems (a broadband absorber for one incidence angle and a broadband absorber with multiple incidence angles) in comparison with similar algorithms in the literature. It has been shown that our algorithm determines either fewer number of layers or smaller overall absorber thickness or both when compared with the results of other algortihms. Finally, the effect of fabrication tolerance is conducted to examine the importance of fewer number of layers.

  AtıfScopus3·WoS1·OpenAlex3

  İncele
• MakaleAçık Erişim2025Scopus SJRQ1/r/bayburt/12751
  A Hybrid Retrieval Method for an Ω-Class Bianisotropic Metamaterial Using Scattering Parameter Method

  Ozturk, Gokhan; Hasar, Ugur Cem; Kaya, Yunus; Korkmaz, Huseyin; Stoyanov, Ivaylo

  In this study, a hybrid retrieval method is proposed to retrieve all terms in the electric and magnetic tensors (along with coupling tensors) of Ω -class bianisotropic metamaterial (MM) slabs using scattering (S-) parameters of both normal incidence TE2 mode and oblique incidence TM2 and TE modes. Compared with other extraction methods in the literature, our retrieval method fully characterizes the MM slab (extracts all constitutive parameters) without necessitating any numerical technique (non-iterative) using fewer wave configurations (two modes) and sample configurations (one configuration). Contrary to two sample configurations required in the application of previous retrieval methods in the literature, one sample configuration (with and without its rotation in the transverse plane) significantly decreases the effect of fabrication tolerances on the accuracy of extraction. The proposed extraction method is first validated by a bulk MM slab synthesized by the Lorentz and Drude models. Then, it is applied for extracting the electromagnetic properties of two bianisotropic MM slabs in the form of square split-ring-resonators and Ω -shape using their S-parameters simulated by a full wave simulation program. Finally, its accuracy is examined by comparing simulated S-parameters with those reconstructed by using extracted electromagnetic parameters. It is observed that our proposed method determines the constitutive parameters with a relatively higher accuracy in a relatively short amount of time.

  AtıfScopus2·WoS1

  İncele
• MakaleAçık Erişim2025Scopus SJRQ1/r/bayburt/11766
  Soil Permittivity Extraction by Time-Domain Free-Space Calibration-Free Microwave Measurements With No Thickness Information

  Hasar, Ugur Cem; Korkmaz, Huseyin; Kaya, Yunus; Iliev, Teodor

  An attractive microwave free-space method is proposed for permittivity extraction of soil samples using calibration-free time-domain measurements. Different from other similar methods in the literature which use the layer-stripping approach in the forward direction in the extraction process, its formalism is based on the layer-stripping approach in the backward direction, whereby allowing extraction of permittivity from interfacial reflection coefficient only without resorting to any thickness information, especially useful for time-domain analysis of multilayer structures having multiple reflection terms. Effects of angle misalignment, loss, and surface roughness on the extraction performance of the proposed method (PM) are analyzed by numerical examples. Permittivity measurements of three low-loss flat solid samples [polypropylene (PP), polyethylene (PE), and polyoxymethylene (POM)] were first performed by a free-space setup operating over 1–18-GHz frequency range to validate our methodology and compare its accuracy against other similar methods in the literature. Thereafter, permittivity measurements of two soil samples sieved with similar and different sizes (coarse- and fine-grained soil samples) by the same free-space setup were then considered to assess the applicability and performance of our method for electromagnetic property analysis of homogeneous and partially inhomogeneous soil samples.

  AtıfScopus9·WoS6·OpenAlex8

  İncele
• MakaleAçık Erişim2025Scopus SJRQ1/r/bayburt/11399
  Transient Plane Wave Transmission Through an N-Layer Multilayer Structure with Bianisotropic Behavior

  Cem Hasar, Ugur; Kaya, Yunus; Korkmaz, Huseyin; Iliev, Teodor

  An analysis based on electromagnetic reflection and transmission properties of multilayer structures are in general needed to get more information about their electromagnetic responses before their implementation for some specific applications involving absorption, shielding, and diagnosis. Such an analysis could be exercised by either frequency-domain or time-domain. While the former one is based on the steady-state response, the latter one is based on the transient response which thus provides more information about electromagnetic properties of multilayer structures. A procedure relying on a direct theoretical time-domain analysis is preferable to a time-domain analysis based on computational procedures such as the finite-time-difference-domain or the fast Fourier transform. In this study, a series presentation of transient plane wave transmission coefficient of N-layer composite structures involving bianisotropic behavior is derived for the first time in the literature in terms of reduced transmission coefficients (the concept of subregion). The wave matrix approach is applied for the theoretical analysis of the reduced transmission coefficient after application of the concept of subregion. Implementation of this concept to our problem is presented step-by-step to make a clear understanding of its application to bianisotropic multilayer structures. The derived reduced transmission coefficient is validated by different multilayer structures (different layer numbers, different layer lengths, and different polarizations) composed of individual layers whose electromagnetic responses are synthesized by the Lorentz dispersion model. Advantages and limitations of the derived formalism are also presented.

  İncele
• MakaleYalnız künye2025Scopus SJRQ1/r/bayburt/11358
  Multi-functional, multi-band, low-profile, ultra-thin, and cost-effective metasurface-based polarization converter

  Kaya, Yunus; Hasar, Ugur Cem; Ozturk, Hamdullah; Ozturk, Gokhan

  This article presents a polarization converter (PC) that demonstrates linear polarization (LP) to LP (LP–LP), circular polarization (CP) to CP (CP–CP), and LP to CP (LP–CP) conversion performance in microwave C-band (4–8 GHz), X-band (8–12 GHz), Ku-band (12–18 GHz), and K-band (18–27 GHz). The designed converter performs LP–LP conversion in the frequency ranges of 6.414–6.771 GHz, 10.681–12.160 GHz, and 18.093–19.045 GHz, CP–CP conversion in the same frequency ranges (6.414–6.771 GHz, 10.681–12.160 GHz, and 18.093–19.045 GHz), and LP–CP conversion in the frequency ranges of 7.374–9.414 GHz and 13.792–16.777 GHz. It is single-layer, metasurface-based, reflection-type (because it consists of a metasurface-substrate-metal ground adaptation), multi-band (five bands), multi-functional (because it shows all three LP–LP, LP–CP, and CP–CP conversions), ultra-thin (with a substrate thickness of 1.6 mm (0.034λ)), low-profile, and cost-effective (since relatively cheaper and easily available FR4 dielectric material is used). Simulations for the designed PC have been carried out by the 3D full electromagnetic simulation program — the Computer Simulation Technology (CST) Studio Suite. The performance analysis of the designed converter was carried out according to the reflection coefficients in the frequency range of 4–21 GHz. It was fabricated using the traditional printed circuit board production method, and its performance was validated in microwave X-band by free-space microwave measurements. More information about the conversion mechanism of the converter was also provided by parametric study and surface current analysis. It is observed that the PC design, which has wide angular independence (50°), can be configured to be efficiently used in radar cross section (RCS) reduction and stealth applications.

  AtıfScopus10·WoS10·OpenAlex8

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