Browsing by Author "Ertekin, Zeynep"

Now showing 1 - 12 of 12

Citation - Scopus: 1
A Broadband Lens Loaded Vivaldi Antenna for Sub-6 GHz/mm Wave 5G Applications and Wideband Nondestructive Material Characterization
(Institute of Electrical and Electronics Engineers Inc., 2024) Berker Colak; Zeynep Ertekin; Mustafa Seçmen; Colak, Berker; Ertekin, Zeynep; Secmen, Mustafa
This study presents a broadband and compact antipodal Vivaldi antenna design and production having an improved gain characteristic with the addition of a dielectric lens made of PLA. The proposed antenna has measured VSWR of less than 2.1 through the broadband frequency of 3.3-43.5 GHz and has more than 6.5 dBi measured gain above 8.5 GHz (up to 43.5 GHz). The antenna which can fit in a cube with just 4.8 cm edge has low-cost and easy manufacturing. It can meet the need of multiple antennas due to its broad frequency range (from S-band to Ka-band) which covers different applications such as wideband nondestructive material characterization and testing. Since the proposed antenna covers sub-6 GHz (3.3 GHz 5.8 GHz) and mmWave (26 38 41 GHz) 5G frequencies it can be also used in base stations with MIMO or array configuration. © 2024 Elsevier B.V. All rights reserved.
Analysis and Classification of Air Disc Brake Sounds in Time and Frequency Domain
(IEEE, 2018) Zeynep Ertekin; Nalan Ozkurt; Cem Yilmaz; Yilmaz, Cem; Ertekin, Zeynep; Ozkurt, Nalan
In this study analysis and classification of audio data collected from faulty air disc brakes has been carried out by Fourier Transform (FT). The sound data have been recorded by 2 identical Norsonic Type 1228 microphones in the laboratory of Ege Fren A.S. on a vehicle. The recorded data set which has been transferred into computer by a data acquisition board has been analyzed in Matlab. Number of zero crossings, mean variance entropy and spectral rolloff of Fourier coefficients have been used as features in order to distinguish normal and faulty brakes. These features have been classified with 10x10 crossvalidation by using kth nearest neighbour algorithm with a success rate of 96.23 %
Carbon nanostructures for automotive and aerospace applications
(Springer International Publishing, 2024) Mustafa Erol; Sibel Demiroğlu Mustafov; Salih Alper Akalin; Begum Uzunbayir; Erdem Tevfik Ozdemir; Berkay Coskun; Zeynep Ertekin; Ertekin, Zeynep; Özdemir, Erdem Tevfik; Erol, Mustafa; Uzunbayir, Begüm; Mustafov, Sibel Demiroglu; Akalin, Salih Alper; Coskun, Berkay
The carbon nanostructures which exhibited great potential for various applications have attracted tremendous attention from scientific and technological fields for more than two decades. It is anticipated that the potential applications of these advanced materials thanks to the desired motivation received from innovation and sustainability especially in automotive and aerospace applications will have a major impact on future vehicles. Besides functional carbon-based nanostructures have been widely exploited as filler materials over the past few years to enhance the efficiency of structural and nonstructural composites which are utilized in the manufacture of automobiles and aircraft. In this chapter exhaustive information about the recent applications of carbon nanostructures is presented under such titles covering the body components crucial systems etc. in the automotive and aerospace industry by considering their potential future applications as well. Research trends and innovations in carbon-based nanomaterials utilized in the aforementioned fields with functionalities such as sensing energy storage protective coatings and shielding are examined in terms of their present and future states. © 2025 Elsevier B.V. All rights reserved.
Disk Fren Sistemlerinde Dalgacık Tepeleri Yöntemi ile Ses Analizi
(2017) NALAN ÖZKURT; ZEYNEP ERTEKİN; cem yılmaz; Yılmaz, Cem; Ertekin, Zeynep; Özkurt, Nalan
Bu çalışmada hatalı disk fren sistemlerinden gelen seslerin dalgacık tepeleri yaklaşımı ile analizi gerçekleştirilmiştir. Bu sesler iki adet Norsonic Type 1228 mikrofon ile laboratuvar ortamında ve araç üzerinde kaydedilmiştir. Bir veri toplama kartı aracılığı ile bilgisayara aktarılan ses kayıtları Matlab ile analiz edilmiş normal fren sesleri ile istenmeyen sesleri ayırt etmek için Dalgacık Tepeleri yaklaşımı kullanılmıştır ve fren seslerinin dalgacık tepesi matrisleri için entropi değerleri bulunmuştur. İnceleme sonucunda hatalı frenlerden gelen sinyallerden hesaplanan entropilerinin daha yüksek olduğu ve bu değerlerin ayırıcı bir öznitelik olarak hata analizinde kullanılabileceği tespit edilmiştir
Citation - WoS: 1
Electromagnetic Interference Shielding Effectiveness Performances of Screen Printing Ink and Expanded Graphite Based Composite at X and Ku Bands
(IEEE, 2023) Zeynep Ertekin; Mustafa Secmen; Mustafa Erol; Erol, Mustafa; Ertekin, Zeynep; Secmen, Mustafa
In this study electromagnetic shielding effectiveness and microwave properties (permittivity and permeability) of the expanded graphite (eGR) embedded in screen printing ink (SPI) were investigated. The experimentally measured scattering parameters were utilized within the Nicolson-Ross-Weir (NRW) algorithm to obtain the intrinsic properties at microwave frequencies. Then these parameters were fed into CST Microwave Studio to check the homogeneity behavior of the proposed sample. Initially a composite containing 7.9 wt% eGR was chosen and all the measurements in experimental setup (solely in waveguide environment) and CST simulations (waveguide and free-space) were performed for the proposed material. About 10 dB/mm shielding efficiency values were satisfied at X and Ku bands (8-18.4 GHz) and homogenous distribution was observed. Afterwards a superior composite containing higher eGR concentration was searched with a trade-off the thickness and the concentration/cost. At least 57 dB and at most 77 dB shielding effectiveness values were measured for a 2 mm thickness sample having 16 wt% eGR which results in more than 25 dB/mm shielding effectiveness at X and Ku bands.
Citation - WoS: 4
Citation - Scopus: 5
Electromagnetic Interference Shielding Performance of Ionic Liquid Modified Carbon Black and Graphite in Polyvinylidene fluoride at Ku-Band
(IEEE, 2019) Zeynep Ertekin; Mustafa Secmen; Mustafa Erol; Erol, Mustafa; Ertekin, Zeynep; Secmen, Mustafa
In this study carbon black and/or graphite incorporated with polyvinylidene difluoride (PVDF) composites giving sufficiently high electromagnetic shielding properties at microwave frequencies are synthesized. Micro-scale carbon black and graphite particles are modified by ionic liquid to improve interference shielding properties of PVDF based composites. The negatively charged carbon black and graphite particles are interacted by positively charged imidazolium ring to form ion pairs being embedded in PVDF. The effects of nanoscale hematite magnetite maghemite and silver nanoparticles (AgNps) on carbon black incorporated PVDF graphite incorporated PVDF and performances of carbon black-PVDF/graphite-PVDF double-layer composites are investigated for the frequency range of 12-18.4 CHz at Ku-band. Among all the composite samples each having 4 mm thickness double-layer samples exhibit the strongest EMI shielding effectiveness by giving up to 35 dB at minimum in the given frequency range.
Citation - WoS: 15
Citation - Scopus: 14
Electromagnetic shielding effectiveness and microwave properties of expanded graphite-ionic liquid co-doped PVDF
(Springer, 2023) Zeynep Ertekin; Mustafa Seçmen; Mustafa Erol; Erol, Mustafa; Ertekin, Zeynep; Secmen, Mustafa
Polymer-based dielectric materials exhibiting high permittivity and high dielectric loss can be preferred in electromagnetic interference shielding due to providing lightweight and better corrosion characteristics as compared to heavy metals. In this work modified carbon black (CB) graphite (GR) and expanded graphite (e-GR) are incorporated with an ionic liquid, 1-Butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF4) in a polyvinylidene fluoride (PVDF) matrix in form of their binary alloys. Electromagnetic shielding effectiveness (SE) and complex permittivity/permeability characteristics of synthesized materials are investigated and measured both in X and Ku band waveguides. The addition of the [BMIM]BF4 into material is observed to enhance ionic conductivity as well as polarizability of the designed composites. The ionic liquid (IL) comprising and IL-free e-GR based composites are measured to give minimum 32.7 dB and 28.1 dB shielding effectiveness along X-band and minimum 39.5 dB and 35.5 dB shielding effectiveness along Ku-band frequency ranges for materials having 3.00 mm sample thicknesses respectively. In comparison with the modified CB and GR the e-GR exhibits better dispersion and superior SE values in the PVDF matrix. In addition to homogeneity observations obtained from scanning electron microscope (SEM) an electromagnetic approach to check homogeneity of the synthesized composites is proposed to the literature which compares shielding effectiveness values per unit thickness (dB/mm) calculated from S-parameter measurements with vector network analyzer (VNA) and calculated from permittivity/permeability values being extracted with Nicolson-Ross-Weir (NRW) algorithm. The homogeneity of composites is found sufficient and more than 9.5 dB/mm and 11.5 dB/mm shielding effectiveness for IL e-GR composite are obtained at X and Ku-bands respectively. © 2023 Elsevier B.V. All rights reserved.
Citation - WoS: 3
Citation - Scopus: 3
Enhancing electromagnetic interference shielding performance of polyester fabrics through composite polymer coating with metal oxides and expanded graphite
(SPRINGER, 2024) Erdem Tevfik Ozdemir; Zeynep Ertekin; Sukran Kara; Mustafa Erol; Mustafa Secmen; Erol, Mustafa; Ertekin, Zeynep; Ozdemir, Erdem Tevfik; Kara, Sukran; Secmen, Mustafa
Radio frequency (RF) devices in which use of high frequency electromagnetic waves may cause electromagnetic interference (EMI) have been an essential part of the human being due to their large area applications especially as transmitters receivers computers televisions and mobile phones. However the pollution caused by RF and/or EMI should not be underestimated. For this reason studies have been carried out to develop shielding properties against EMI of various products in particular of wearable fabrics. With this manner in this study composite polymer coated textiles were designed and produced by utilizing polyester base fabric polyvinylidene fluoride coating polymer (matrix) and some additives (fillers) such as expanded graphite (E-GR) bismuth oxide (Bi2O3) and copper oxide micro/nano-particles. The experimental design on the preparation of the samples based on the unary binary and ternary combinations of the additives was created to investigate their combined effects on the EMI shielding performances. Samples were characterized by scanning electron microscopy energy dispersive spectroscopy fourier-transform infrared spectroscopy and vector network analyzer. According to the results it can be inferred that the fillers are homogeneously distributed along the all surface without a chemical interaction with the matrix of continuous and compact composite coatings. Among the samples the highest EMI performance with 19 dB shielding effectiveness was recorded for the sample containing E-GR and Bi2O3 in which of the 98.74% electromagnetic signals were blocked along 8-12 GHz frequency range.
Citation - WoS: 9
Citation - Scopus: 11
La:ZnO nanoparticles: an investigation on structural- optical- and microwave properties
(SPRINGER, 2024) Neslihan Sakar; Zeynep Ertekin; Sibel Oguzlar; Mustafa Erol; Oguzlar, Sibel; Erol, Mustafa; Ertekin, Zeynep; Sakar, Neslihan
This paper presents the utilization of ethylene glycol monomethyl ether (EGME) during the synthesis of ZnO and La:ZnO with two tasks as a solvent and a fuel source within the gel combustion technique. The use of EGME for this purpose provides one-step production of the nanoparticles (NPs) and saves a considerable amount of time. The detailed characterization of the nanoparticles was carried out by X-ray diffractometer (XRD) scanning electron microscope (SEM) particle size analyzer Fourier transform infrared spectroscopy (FTIR) X-ray photoelectron spectroscopy (XPS) photoluminescence (PL) and Vector Network Analyzer (VNA) measurements respectively. The NPs exhibited a hexagonal wurtzite structure with good crystallinity and a porous spongy morphology. The photoluminescence emission maxima of the synthesized NPs appeared at 500 560 and 676 nm upon excitation by the 372 nm of excitation. La:ZnO NPs showed significantly better photoluminescent characteristics than La-free ZnO forms. When excited at the same wavelength La-free ZnO 3% and 7% La:ZnO exhibited 92 45 and 35 mu s average decay times respectively. Finally the microwave properties of the relative complex permittivity and permeability characteristics were also investigated and discussed in detail which were derived from the scattering parameters of S11 and S21 in the X band regime.
Citation - Scopus: 2
Low-Cost Carbon-Based Electromagnetic Shielding Material Design at X and Ku Bands for Electronics Fabric and Wearable Equipment
(Institute of Electrical and Electronics Engineers Inc., 2021) Zeynep Ertekin; Mustafa Seçmen; Mustafa Erol; Erol, Mustafa; Ertekin, Zeynep; Secmen, Mustafa
In this study micro scale carbon black and graphite particles are utilized in a water based and robust polymeric matrix to provide an effective electromagnetic interference (EMI) shielding material along X and Ku bands. The particles are embedded into screen printing ink (SPI) in order to gain conductivity which results in low-cost and eco-friendly composite. Scattering parameters of synthesized materials are measured by a Vector Network Analyzer and these data are used in Weir's algorithm to compute relative complex permittivity and permeability of the composites. The offered SPI based composite gives approximately 30 dB EMI shielding at X and Ku band for a 3 mm thickness. It can be used in the coating of devices instruments systems or even walls if required. It is also highly compatible with many kinds of fabric which makes it a good candidate for wearable electronics and occupational health and safety equipment. © 2024 Elsevier B.V. All rights reserved.
Mı̇krodalga frekanslarında karbon bazlı elektromanyetı̇k gı̇rı̇şı̇m kalkanlama malzemeleri tasarımı ve gerçekleştirilmesi
(2024) Ertekin, Zeynep; Seçmen, Mustafa
The exchange of electromagnetic signals is fundamental to personal devices such as computers and telephones, as well as more complex systems such as antennas and radars used in applications such as weather forecasting, satellite communications, navigation and national security. It is essential that these devices operate within the limits of electromagnetic compatibility (EMC). This prevents them from interfering with or damaging each other. However, interference and interaction can sometimes occur when electromagnetic signals are exchanged at close frequencies. These disturbances can be the cause of equipment or system malfunction or data corruption or loss. This is why protecting equipment which uses electromagnetic signals is vital. This thesis investigates the development, optimisation and implementation of two novel electromagnetic shielding composites, both of which use expanded graphite as a conductive filler in polymer matrices to provide effective shielding against electromagnetic interference (EMI). The focus of the research is on the actual EMI shielding performance of the composites rather than ideal conditions. Scattering data were collected using a vector network analyser, microwave parameters calculated using the Nicolson-Ross-Weir algorithm and simulations performed in CST to reduce experimental material costs and improve accuracy and efficiency of the proposed composite. The first of these composites, composed of ionic liquid and expanded graphite co-doped PVDF (Poly(vinylidene difluoride)), demonstrated sufficient electromagnetic shielding success in the 8-18 GHz range. However, it was discarded due to its high cost. The second composite, a structure containing 11 wt.% expanded graphite embedded in screen printing ink, proved to be both cost-effective and successful in broadband applications, providing effective electromagnetic shielding as confirmed by both simulation and experimental methods. Electromagnetic analyses were carried out under both ideal conditions (waveguide) and realistic lossy conditions (free space). A total of seven different methods were used - three experimental and four simulation techniques. As a contribution to the literature, the electromagnetic homogeneity of the novel composite material was evaluated for the first time using two different methods. Homogeneity percentages were obtained over a broadband frequency range (2-30 GHz). For a real-world application, a cube made from the designed composite structure was tested in both experimental and simulation environments. Several antennas operating in different frequency regimes were placed inside the cube to assess its protection from electromagnetic signals. The extent to which these antennas were affected by external electromagnetic signals was investigated. This cube application is a contribution to the literature by demonstrating its use in both electromagnetic shielding and absorption test applications. The material characterisation of this composite structure, presented for the first time in the literature, has also been carried out, underlining its potential effectiveness and practical application.
Otomotiv fren sistemleri için ses analizi
(2018) Ertekin, Zeynep; Özkurt, Nalan
In this thesis, air disc brakes are investigated in terms of noise using signal processing tools. Inspired by the literature view, sound and vibration data are used in order to detect faults, moreover; many algorithms are proposed to classify the type of the dysfunction. Sounds recorded from a noiseless, a less noisy and a noisy brake by a data acquisition board, are analyzed in time domain, in frequency domain and in time-frequency domain, respectively. The mean, variance, number of zero crossings, maximum, minimum, and entropy of time windows are calculated and the brakes are classified as noisy and less noisy using k nearest neighbor classification algorithm. The same procedure is repeated for frequency domain considering features mean, variance, spectral roll-off, maximum and entropy. Since time-frequency domain analysis will reveal the characteristics of the sound signals better, qualitative and quantitative analysis has been accomplished by using continuous and discrete wavelet transform. It has been shown that the discrimination between the noisy and less noisy brakes signals can be observed in time-frequency domain clearly. Key Words: Disc brake systems, noise, wavelet transform, frequency domain, k nearest neighbor (k-NN algorithm)