Fen Bilimleri Enstitüsü / Science Institutehttp://hdl.handle.net/11727/13922024-03-28T19:02:31Z2024-03-28T19:02:31ZEffects of Repair Techniques and Scarf Angles on Mechanical Performance of Composite MaterialsKaraduman, Beyza NazElaldi, Farukhttp://hdl.handle.net/11727/119572024-03-27T08:31:18Z2023-01-01T00:00:00ZEffects of Repair Techniques and Scarf Angles on Mechanical Performance of Composite Materials
Karaduman, Beyza Naz; Elaldi, Faruk
Today, composite materials, which have the advantage of strength and lightness ratio, have gained great importance especially in the aeronautical industry and automotive sector. With widespread use of composites, the repair of damages caused by external factors has also become an important research topic. In this study, the effects of different repair methods and scarf angles on the mechanical performance of the material were investigated. Scarf angles of 20 degrees, 30 degrees, and 45 degrees have been selected in order not to create too many scarf areas and to find a quick repair method. Also, a comparison of single scarf and double scarf repair was made to find a more robust solution. The samples were produced from carbon fiber prepreg and with the [45/0/90/0/45](2s) fiber orientation. Tensile, compression, and flexural (3-point bending) tests according to ASTM standards were applied to composite samples prepared with single scarf and double scarf repair configurations at different angles. The stress-strain curves obtained as a result of the tests showed that the specimens repaired at 20 degrees had the highest strength. In addition, it has been determined that the samples repaired with double scarf withstand higher forces compared to the samples repaired with single scarf at the same angle.
2023-01-01T00:00:00ZOmics in Oxidative Stress Tolerance in CropsKayihan, CeyhunEyidogan, Fusunhttp://hdl.handle.net/11727/104622023-08-29T10:36:07Z2019-01-01T00:00:00ZOmics in Oxidative Stress Tolerance in Crops
Kayihan, Ceyhun; Eyidogan, Fusun
2019-01-01T00:00:00ZComparison of Intelligent Classification Techniques by Practicing a Specific Technology AuditBerkol, A.Kara, G.Turk, A.http://hdl.handle.net/11727/96112023-06-15T06:55:03Z2016-01-01T00:00:00ZComparison of Intelligent Classification Techniques by Practicing a Specific Technology Audit
Berkol, A.; Kara, G.; Turk, A.
Technology audit activities arc carried out for assessment of firms' technological requirements, capacity or management capability. The aim of these assessments is to define the weaknesses of firms and develop actions in order to improve firms' technological capacity and/or technology management capability. Generally these activities are implemented with survey questionnaires. These questionnaires can be filled by managers of firms or can be implemented as an interview by independent experts. However, evaluating surveys and preparing useful comments related to results can consume lots of time and also contain lots of biases/subjectivity. In accordance to ease the decision making process and provide more verified/accurate results, we develop a methodology based on an Artificial Neural Network (ANN) algorithm which is aimed to behave like a decision maker. And in this study, we use a synthetic data set which is prepared for assessment of technology management capability of selected 70 Turkish firms.
2016-01-01T00:00:00ZX bant uygulmaları için GaN tabanlı düşük gürültülü yükselteç tasarımıTendürüs Çağlar, Gizemhttp://hdl.handle.net/11727/94682023-06-08T22:40:27Z2022-01-01T00:00:00ZX bant uygulmaları için GaN tabanlı düşük gürültülü yükselteç tasarımı
Tendürüs Çağlar, Gizem
Galyum Nitrür (GaN) tabanlı Yüksek Elektron Hareketli Transistörlerin (HEMT’ler) ortaya çıkışı, özellikle yüksek arıza gerilimleri ve üstün güç işleme yetenekleri nedeniyle dikkatleri üzerine çekmiştir. Bu özellikler, GaN tabanlı Monolitik Mikrodalga Devresi (MMIC) teknolojisi üzerinde çok yüksek verimliliğe sahip yüksek güçlü yükselteçler (HPA) tasarlama şansı verir. GaN HEMT'lere duyulan ihtiyaç, onu yalnızca HPA'lar için değil, aynı zamanda anahtarlar ve düşük gürültülü yükselteçler (LNA) için de giderek daha çekici hale getirdi. GaN HEMT monolitik teknolojisinin ortaya çıkmasıyla birlikte, düşük gürültü yükselteç tercihleri de değişti. GaN tabanlı düşük gürültülü yükselteçler, sisteme gürültü vererek çok düşük güçlü bir sinyali, sinyal-gürültü oranını önemli ölçüde düşürmeden yükselten, genel sistem gürültü katsayısını azaltacak şekilde, devreleri limitleyecek korumaya ihtiyaç duymadan ve hasar görmeden son derece yüksek giriş gücü seviyelerine dayanabilen alıcı aşamaları gerçekleştirmek için en iyi adaylardan biridir. Alıcı devrelerinde düşük gürültülü yükselteçler, antenden alınan sinyale düşük gürültü vererek sinyalin gürültülü kısmını düşürdüğünden iletişim sistemleri için önem arz eder.
GaN HEMT'lerin doğal sağlamlığı nedeniyle, bu cihazlar kullanılarak tasarlanan LNA'lar, koruma devresi olmadan sürekli çalışabilir.
Bu tezde, X bandında çalışan bir MMIC LNA, kaynak dejenerasyonu ile GaN HEMT kullanılarak tasarlanmıştır. Pasif devre elemanları, transistörler ve MMIC NANOTAM’da geliştirilen Silisyum Karbür (SiC) tabanlı 0,15 μm/0,2 μm AlGaN/GaN HEMT mikrofabrikasyon süreci ile üretilmiştir. Üretim iki aşamadan oluşmaktadır. Sırasıyla önyüz ve arkayüz adımlarını içermektedir.
Üretilen transistörlerin doğrusal akım (DC), küçük işaret, büyük işaret ve gürültü katsayısı ölçümleri yapılmıştır. LNA tasarımı için uygun HEMT seçilmiş ve tasarım süreci, kaynak dejenere HEMT kullanılarak tek kademeli yapıda gerçeklenmiştir. Kaynak dejenere HEMT topolojisi hem kolay giriş eşlemesi hemde kararlılık sağlamıştır. GaN tabanlı LNA MMIC tasarımı yapılmış üretim sonrasında wafer üzerinde oda sıcaklığında ölçümleri alınmış ve en iyi sonuçları aktarılmıştır. LNA tasarımı 8-11 GHz arasında 7 dB üzerinde küçük işaret kazancı, 8,5 dB’den iyi giriş ve çıkış kayıpları, 1,1 dB’den iyi gürültü katsayısı, 17,19 dBm çıkış gücü ve %12,64 akaç verimliliği sağlamaktadır.
The emergence of Gallium Nitride (GaN)-based High Electron Mobility Transistors (HEMTs) devices has attracted attention, especially due to their high breakdown voltages and superior power handling capabilities. These features give a chance to design very high-efficiency high power amplifiers (HPA) on GaN-based Monolithic Microwave Circuit (MMIC) technology. The need for GaN HEMTs has made it increasingly attractive for this and switches and low-noise amplifiers (LNAs). With the advent of GaN HEMT monolithic technology, low noise amplifier preferences have also changed. GaN-based low-noise amplifiers (LNAs) can deliver noise to the system, amplifying a very low-power signal without significantly reducing the signal-to-noise ratio, reducing the overall system noise coefficient, without the need for protection and damage to limit circuits, to extremely high input power levels. It is one of the best candidates to perform the receiving stages that can withstand. Low noise amplifiers in receiver circuits are important for communication systems as they reduce the signal received from the antenna by giving low noise.
Due to the inherent robustness of GaN HEMTs, LNAs designed using these devices can operate continuously without protection circuitry.
In this thesis, an X-band MMIC LNA is designed using GaN HEMT with source degeneration. Passive circuit elements, transistors, and Silicon Carbide (SiC) based 0,15 μm/0,2 μm AlGaN/GaN HEMT microfabrication process developed in MMIC NANOTAM. Production consists of two stages. It includes the front and back steps, respectively.
The produced transistors made the linear current (DC), small signal, and large-signal and noise coefficient measurements. The appropriate HEMT was selected for the LNA design and the design process was carried out in a single-stage structure using the source degenerate HEMT. The source degenerate HEMT topology provided both easy input mapping and stability. GaN-based LNA MMIC was designed, and after the production, measurements were taken on the wafer at room temperature and the best results were reported. LNA design provides a small signal gain of over 7 dB between 8-11 GHz, input and output losses better than 8,5 dB, noise coefficient better than 1,1 dB, the output power of 17,19 dBm and drain efficiency of 12,64%.
2022-01-01T00:00:00Z