Johari, Mohd Hilmi; Ismail, Ismayadi; Azis, Rabaah Syahidah; Tim, Chan Kar; Nafis, Nur Biha Mohamed; Ertugrul, Mehmet; Karakaş, Ibrahim Hakki

This study investigates the synthesis, microstructural characteristics, magnetic properties, and electromagnetic wave absorption performance of nickel ferrite (NiFe2O4) composites reinforced with multi-walled carbon nanotubes (MWCNTs) synthesized via the microwave-assisted combustion (MAC) method. X-ray diffraction (XRD) analysis confirmed the desired structure of NiFe2O4 and the successful integration of MWCNTs within the NiFe2O4 matrix. Field emission scanning electron microscopy (FESEM) analysis revealed the entanglement of MWCNTs and their significant impact on hindering particle growth, resulting in a finer particle structure. The reduction in average particle size from 1.317 µm for pure NiFe2O4 to 0.436 µm for NiFe2O4 with 2wt% MWCNT, representing approximately a 66.89% reduction, significantly demonstrates the effectiveness of MWCNTs in limiting particle growth and promoting a more refined particle structure. Magnetic property analyses showed a nuanced interplay between MWCNT concentration and composite behaviour, with the saturation magnetization (Ms) exhibiting substantial enhancement in the NiFe2O4/2wt%MWCNT composite, indicative of effective alignment of magnetic moments. However, a subsequent decrease in Ms at higher MWCNT concentrations (4wt% and 6wt%) suggested potential dilution effects and disruptions in magnetic interactions within the composite. Electromagnetic wave absorption investigations revealed NiFe2O4/4wt%MWCNT as a highly efficient absorber in the Ku-band, with superior impedance matching and a high attenuation constant. The reflection loss (RL) reached a maximum of –17.58 dB at 12.78 GHz, signifying absorption of more than 99% of the incident EM wave in the microwave range. The favourable impedance matching and high attenuation constant contributed to the superior performance of NiFe2O4/4wt%MWCNT compared to pure NiFe2O4 and MWCNT. These findings suggest the potential of NiFe2O4/MWCNT composites for applications in telecommunications, aerospace, and electronics, with opportunities for further optimization and investigation into long-term stability and durability under varying environmental conditions.

AtıfScopus1·WoS2·OpenAlex1

İncele

Teber, Ahmet; Ertugrul, Mehmet; Coşkun, Aykut

Burada, geniş bant yansıtıcı doğrusal polarizasyon (LP) ve dairesel polarizasyon (CP) dönüşümlerini gerçekleştirmek için tek katmanlı, ultra ince, çok işlevli ve yüksek verimli bir meta-yüzey sunulmaktadır. Önerilen meta-yüzey, %97'den fazla verimlilikle %55.2'lik (7.89-13.91 GHz) nispi absorpsiyon bant genişliği (RAB) üzerinde doğrusal polarize dalga için mükemmel bir çapraz polarizasyon dönüştürücü görevi görür. Doğrusal polarize dalgaları 7.2–7.36 GHz frekans aralığında başarıyla dairesel polarize dalgalara dönüştürür. Ek olarak, TE ve TM modları için polarizasyon dönüşüm oranı (PCR) verimlilik özellikleri, 45⁰'ye kadar geniş bir geliş açısı ile tüm X bandında korunur. Sunulan polarizasyon dönüştürücü, 0.07λ0 kalınlık ile ultra ince bir özelliğe sahiptir. Kompakt boyutu, açısal kararlılığı, yüksek verimliliği, basit yapısı ve çok işlevliliği nedeniyle bu polarizasyon dönüştürücü, birçok uygulamada polarizasyon manipülasyonu ve iletişim cihazları için önemli bir adaydır.

AtıfOpenAlex1

İncele

Hasar, Ugur Cem; Kaya, Yunus; Ozturk, Hamdullah; Ertugrul, Mehmet; Ramahi, Omar Mustafa

An effective microwave method is developed for extracting electromagnetic properties of bianisotropic metamaterial (MM) slabs. As a non-iterative method, it utilizes only the one-port (air-backed and metal-backed MM slab) scattering (S-) parameter measurements. This is a useful feature especially for vector network analyzers, such as MS46131A, MS46121B, and R60, performing only one-port S-parameter measurements. Electromagnetic properties of a bianisotropic MM slab formed by C-shaped resonators are measured by an X-band (8.2–12.4 GHz) rectangular waveguide setup. The effect of any gap between the short-circuit termination for metal-backed measurements and the end of the MM slab on extracted electromagnetic properties is also examined for evaluating the possible error for proposed method.

AtıfScopus3·WoS3·OpenAlex5

İncele

Hasar, Hafize; Hasar, Ugur C.; Kaya, Yunus; Ozturk, Hamdullah; Izginli, Mucahit; Oztas, Taskin; Aslan, Nevzat; Ertugrul, Mehmet; Barroso, Joaquim J.; Ramahi, Omar M.

Microwave techniques, as an indirect approach, can be applied for analyzing water content in honey by way of permittivity measurements. However, these techniques require proper calibration to accurately perform such indirect evaluation. Improper calibration standards used in this calibration process could naturally result in a reduction in the accuracy and thus the performance of dielectric characterization using microwaves. Self-calibrating microwave techniques can reduce the effects of imprecise standards and thus improve the performance of microwave measurements by bypassing the requirement of calibration standards. In this study, we develop a self-calibrating microwave measurement technique to determine the relative permittivity of honey samples and implement binary mixing models to predict adulteration levels of water-adulterated honey. From this implementation, it is observed that the parallel-capacitance mixing model could efficiently be applied to determine the concentration of water adulteration by examining the differences between absolute values of the real parts of the measured and predicted complex permittivities of adulterated honey.

AtıfScopus18·WoS16·OpenAlex18

İncele

Hasar, Ugur C.; Ozturk, Gokhan; Kaya, Yunus; Barroso, Joaquim Jose; Ertugrul, Mehmet; Ramahi, Omar M.; Alfaqawi, Mona S. S.

The temporal reflection response of an N-layer composite structure involving bianisotropic behavior is examined for the first time in the literature. Toward this goal, the wave matrix (WM) method, which is fundamental, relatively easier to apply, and compact and iterative suitable for analysis of multilayer structures, is first extended to the analysis of an interface separating two different media involving bianisotropy. Next, the reflection response of the whole structure is derived in terms of series form to better analyze its temporal behavior. Then, frequency-domain and time-domain responses of the whole structure are expressed using a special reflection coefficient (the reduced reflection coefficient) by way of the concept of subregions. A numerical analysis is performed to demonstrate the applicability of our formalism for two different polarization types (perpendicular and parallel).

AtıfScopus3·WoS3·OpenAlex3

İncele

Hasar, Ugur C.; Ozturk, Gokhan; Kaya, Yunus; Alfaqawi, Mona S. S.; Barroso, Joaquim Jose; Ertugrul, Mehmet; Ramahi, Omar M.

A time-domain free-space extraction procedure is proposed to uniquely determine the relative complex permittivity epsilon(r)(omega) based on two sets of natural frequencies of the metal- and air-backed dielectric samples. A graphical analysis is applied for evaluating whether unique epsilon(r)(omega) can be extracted using such natural frequencies. The method is numerically validated using two dielectric samples with different epsilon(omega) for the ideal case (no noise) and under the influence of noise with different signal-to-noise ratios (SNRs).

AtıfScopus1·OpenAlex1

İncele

Hasar, Hafize; Hasar, Ugur C.; Kaya, Yunus; Oztas, Taskin; Canbolat, Mustafa Y.; Aslan, Nevzat; Ertugrul, Mehmet; Ramahi, Omar M.

A new de-embedding line-line method has been proposed for accurate complex relative permittivity ( ε ᵣ ) determination of soil samples loaded into an EIA 1-5/8' coaxial transmission line measurement system. The method has three main features. First, it bypasses the requirement of calibration of this system by using only two identical coaxial lines with different lengths. Second, it does not need any numerical technique for ε ᵣ determination. Third, it does not require knowledge of electromagnetic properties and thickness information of the bead used for supporting soil samples. The method is next validated by simulations performed using a full 3-D electromagnetic simulation program (CST Microwave Studio) and by ε ᵣ measurement of a polyethylene (PE) material. Finally, ε ᵣ values of three air-dried and water-saturated soil samples having 90% or more sand content with different electrical conductivities (ECs) and gathered from different areas of the city Gaziantep in Turkey, were measured.

AtıfScopus18·WoS16·OpenAlex16

İncele

Coskun, Aykut; Hasar, Ugur Cem; Ozmen, Ahmet; Ertugrul, Mehmet

This article presents an ultrathin, broadband, and multipurpose polarization converter design utilizing an anisotropic metasurface for K and Ka band. The proposed polarization converter, which has a single layer F4B as a substrate material with hexagonal-shaped metallic solid structure along with hexagonal ring with diagonal splits on its front surface and a background (a completely metallic surface) on its back, works as not only a circular polarization converter but also a linear polarization to circular polarization (LP to CP) converter. Its polarization conversion rate (PCR) is more than 90% in the frequency range from 17.87 to 43.15 GHz, covering all of the K and Ka bands with a relative bandwidth of 83% under normal incidence case. For incidence angles up to 40°, PCR is observed to be greater than 75% in almost all of the K and Ka bands (except for the frequency range between 24.72 and 27.11 GHz). Furthermore, the proposed design has LP to CP in two different frequency bands, 16.23–16.74 GHz and 48.6–48.8 GHz. The proposed polarization converter, as advantages, is low cost, ultra thin, broadband, and facile, which can be useful in linear cross polarization conversion in K and Ka band applications.

AtıfScopus10·WoS9·OpenAlex10

İncele

Hasar, Ugur C.; Ozturk, Gokhan; Kaya, Yunus; Ertugrul, Mehmet

A time-domain free-space technique has been proposed to extract relative permittivity ( _r ) and effective conductivity ( σ _e ) of low-loss dielectric samples using their metal- and air-backed calibration-free reflected powers. Numerical computations and 3-D electromagnetic simulations were performed to validate the method. A sensitivity analysis was carried out to examine its accuracy. Calibration-free time-domain free-space measurements over 1-12 GHz were conducted by VNA to extract _r and σ _e of polyethylene and polypropylene low-loss samples.

AtıfScopus29·WoS28·OpenAlex29

İncele

Hasar, Ugur C.; Kaya, Yunus; Ozturk, Gokhan; Ertugrul, Mehmet; Korasli, Celal

A broadband, stable, and noniterative free-space method is proposed for dielectric constant ϵr′ determination of low-loss dielectric slabs from reflection-only measurements through simple calibration standards (reflect and air). It is applicable for dispersive samples and does not require thickness information. Simulations of nondisperive and dispersive samples are performed to validate our method. Dielectric constant measurements of polyethylene and polyoxymethylene samples (9-11 GHz) are carried out to examine the accuracy of our method.

AtıfScopus41·WoS37·OpenAlex35

İncele

Hasar, Ugur Cem; Kaya, Yunus; Ozturk, Hamdullah; Izginli, Mucahit; Ertugrul, Mehmet; Barroso, Joaquim Jose; Ramahi, Omar M.

A new deembedding technique is proposed for relative complex permittivity epsilon(r) determination of dielectric materials using gated free-space measurements. Its three main features are 1) it does not require any formal calibration procedure (calibration-free); 2) it is position-insensitive; and 3) it extracts ripple-free epsilon(r) due to gating process. The objective function derived to determine epsilon(r) by the proposed method is validated by free-space measurements of three dielectric samples (polypropylene, polyethylene, and polyoxymethylene). Besides, the accuracy of our method is compared with the accuracy of other calibrationfree and calibration-dependent methods in the literature.

AtıfScopus49·WoS36·OpenAlex44

İncele

Hasar, Ugur C.; Kaya, Yunus; Izginli, Mucahit; Ozturk, Hamdullah; Barroso, Joaquim J.; Ramahi, Omar M.; Ertugrul, Mehmet

A microwave method is proposed to determine the forward and backward propagation constants (gamma ⁺ and gamma ⁻) and the wave impedance ( z_w ) of reciprocal and non-reciprocal microwave networks whose positions are not known within their measurement cells (position-insensitive). The proposed method relies purely on analytical expressions and can also evaluate the reference plane transformation distances. Scattering parameter measurements at the X-band (8.2-12.4 GHz) of a reciprocal network (a waveguide straight) and a non-reciprocal network (a microwave phase shifter) arbitrarily positioned into their measurement cells were conducted to retrieve gamma ⁺, gamma ⁻, and z_w for validation of our method and testing its position-insensitive property. The importance of the method becomes apparent when compared to conventional methods whose accuracy is based on precise determination of the reference planes.

AtıfScopus9·WoS9·OpenAlex9

İncele

Hasar, Ugur Cem; Kaya, Yunus; Ozturk, Hamdullah; Izginli, Mucahit; Barroso, Joaquim Jose; Ramahi, Omar M.; Ertugrul, Mehmet

A free-space time-domain method is proposed to retrieve dielectric constant (epsilon r), conductivity (sigma e), and thickness (d) of metal-backed low-loss dielectric samples using calibration-independent reflected power peak measurements. Its algorithm is validated by numerical calculations and simulations (CST Microwave Studio) using a sine-modulated Gaussian window. A sensitivity analysis is followed to examine its performance considering the dependencies of reflected power peaks with respect to epsilon r and sigma e. Free-space time-domain measurements have been implemented after transforming frequency-domain measurements into time-domain ones to extract epsilon r, sigma e, and d of polypropylene, polyethylene, and polyoxymethylene samples.

AtıfScopus48·WoS42·OpenAlex43

İncele

Hasar, Ugur Cem; Ozturk, Gokhan; Kaya, Yunus; Bute, Musa; Karaaslan, Muharrem; Barroso, Joaquim J.; Ramahi, Omar M.; Ertugrul, Mehmet

An extraction technique is proposed for electromagnetic characterization of metal-backed multilayer metamaterial (MM) structures demonstrating reflection-asymmetric property. It uses recursive scattering parameters for direct and reversed configurations of a multilayer structure. The algorithm was validated by comparing the extracted electromagnetic properties of multilayer structures composed of different MM unit cells with those determined by one-layer-only S-parameter methods. Two-layer and three-layer multilayer structures composed of MM slabs with C-shaped and Omega-shaped rings and an FR4 material were fabricated and measured for experimental validation. A sensitivity analysis was also conducted to quantitatively evaluate the performance of our method against a small air gap between the multilayer structures and the short-circuit termination and between adjacent MM slabs within these structures. Strong agreement was observed between the resulted obtained using our method and measurements.

AtıfScopus10·WoS10·OpenAlex10

İncele

Hasar, Ugur C.; Kaya, Yunus; Ertugrul, Mehmet

In this article have proposed a new calibration-free line-line method for propagation constant (gamma) determination of homogeneous nonreciprocal networks or lines with symmetric reflection property. To achieve our goal, wave-cascading matrices for impedance, amplitude, and phase changes for a line step from a homogeneous reciprocal network or line to a homogeneous nonreciprocal network or line (and vice versa). Two different approaches based on the proposed line-line method are proposed for unique extraction of gamma in forward and backward directions. Measurements of gamma for two reciprocal lines (waveguide straights at X-band and Ku-band with different lengths) and a nonreciprocal line (microwave phase shifter) were first carried out and then compared with measured gamma of these lines by different methods to validate our method and monitor its accuracy.

AtıfWoS4·OpenAlex5

İncele

Hasar, Ugur C.; Ozturk, Gokhan; Kaya, Yunus; Barroso, Joaquim J.; Ertugrul, Mehmet

We propose a simple and accurate microwave extraction procedure for full electromagnetic characterization of \Omega -class bianisotropic metamaterial (MM) slabs from normal incidence scattering (S-) parameters using TE1, TE2, and TE3 modes. Its closed-form nature (no need for any numerical analysis and optimization toolbox) and less requirement (a total of seven S-parameters) demonstrate the advantage of our method over other methods in the literature. Our approach was validated and its accuracy was verified by S-parameters, through a full electromagnetic simulation program - CST Microwave Studio, of an edge-coupled \Omega -class split-ring-resonator MM slab.

AtıfScopus15·WoS13·OpenAlex14

İncele

Hasar, Ugur Cem; Ozturk, Hamdullah; Kaya, Yunus; Izginli, Mucahit; Ertugrul, Mehmet

A microwave method has been proposed for constitutive parameters' extraction of samples on a known substrate. The advantage of this method is that it relies on noniterative reflection-only (air-and metal-backed) scattering (S-) parameters so that it is a good candidate for the characterization of samples when only one-port measurements are available. It is validated by the X-band (8.2-12.4 GHz) waveguide S-parameter measurements. A sensitivity analysis is followed to evaluate and improve the performance of our method.

AtıfScopus5·WoS5·OpenAlex3

İncele

Hasar, Hafize; Hasar, Ugur Cem; Kaya, Yunus; Ozturk, Hamdullah; Izginli, Mucahit; Ozbek, Ibrahim Yucel; Oztas, Taskin; Canbolat, Mustafa Yildirim; Ertugrul, Mehmet

An efficient de-embedding air-line microwave method has been proposed for accurate relative complex permittivity, εr=εr′−iεr′′, measurement of water-adulteration level within honey. It could be effectively applied to eliminate the errors arising from usage of imperfect calibration standards because it bypasses the requirement of these standards. Its accuracy is improved by utilizing the unitary and similarity properties of a passive two-port network, and then is compared with the accuracy of a calibration-dependent method present in the literature by using normalized root-mean-square-error (N-RMSE) values of εr′ and εr′′ of distilled water, in reference to the Debye value. From this comparison, it is observed that N-RMSE values calculated for εr′ (and εr′′) by using this calibration-dependent method and the (improved) proposed method are, respectively, around 0.1955 (0.1002) and 0.1962 (1.1067), indicating a good agreement between them. After validation the proposed de-embedding method using distilled water measurements, tested pure honey was adulterated with distilled water by different percentage values δ ranging from 1% to 10% in 1% increments. It is observed that the maximum distance between extracted εr′ (or εr′′) values of adulterated honey by the applied calibration-dependent method and the proposed method is less than 2%. Afterward, an empirical formula was devised to fit εr′ and εr′′ values from measured εr of water-adulterated honey with various δ levels. It is noted that extracted εr′ is much more better fitted than extracted εr′′, especially for δ≤4. Next, an optimization process is followed to evaluate the frequency for optimum prediction of adulteration levels using the empirical formula based on εr′ or εr′′. It is noticed that optimized δ values using the empirical formula based on εr′ (with an average prediction error of around 0.071 at 4.5 GHz) are superior to optimized δ values using the empirical formula based on εr′′ (with an average prediction error of around 0.085 at 4.2 GHz) for prediction of previously known δ values. Sensitivity and uncertainty analyses were performed to assess and improve the accuracy of the proposed method.

AtıfScopus24·WoS23·OpenAlex24

İncele

Hasar, Ugur Cem; Kaya, Yunus; Ozturk, Gokhan; Ertugrul, Mehmet

An analysis was performed for examining the consequences of sample deformation in longitudinal axis in the sample-loaded non-resonant waveguide techniques. Vertical and horizontal deformations were first simulated to understand the change in field distributions and corresponding scattering parameters. Then, effects of sample length, dielectric constant, and loss factor for these deformations on extracted electromagnetic properties were analyzed using simulated results. Finally, S-parameter measurements were carried out to understand the effect of vertical deformation on permittivity results and to examine any improper sample preparation by hand-made and machine-made samples by applying a statistical model based on mean, standard deviation, coefficient of variation, and confidence interval. It was noted that extracted dielectric constants of each tested dielectric sample (polyethylene, polypropylene, polyvinyl-chloride) were within the confidence interval range of 90% while their retrieved loss factors were within the confidence interval range of 90%, 95%, or 98%.

AtıfScopus3·WoS3·OpenAlex3

İncele

Hasar, Ugur C.; Ozturk, Gokhan; Barroso, Joaquim J.; Gurbuz, Tolga U.; Kaya, Yunus; Ertugrul, Mehmet

A graphical method is extended to and applied for visual inspection of solution patterns (region of complex natural frequencies sₙ) in the complexs-plane for dispersive materials characterized by the Debye and Lorentz models. These patterns are in the form of exponential decay and C-shaped profiles for the Debye and Lorentz models, respectively. Their forms are observed to be affected (e.g., moving left/right) in different manners with a variation of dispersion parameters. This method, thanks to its visual inspection capability, can help in analyzing/synthesizing filters and frequency-selective surfaces.

AtıfScopus6·WoS6·OpenAlex7

İncele