Browsing by Author "Tuncer, Ahmet Turgut"

Now showing 1 - 3 of 3

Kalkanlama sonlandırma metotlarının yıldırımın uçaklar üzerindeki dolaylı etkilerine karşı başarımının incelenmesi
(Başkent Üniversitesi Fen Bilimler Enstitüsü, 2023) Atalay, Emre; Tuncer, Ahmet Turgut
Yıldırım yüksek akım ve yüksek voltajın ani olarak boşaldığı bir doğa olayıdır. Bu doğa olayı bulutlar arasında, bulut içinde ya da bulut ile yeryüzü arasında olacak şekilde meydana gelebilmektedir. Hava araçlarına da yıldırım çarpma riski vardır. Günümüzde yıldırım çarpmasını önleyici bir sistem mevcut değildir. Bunun için yıldırımın etkileri azaltılmaya çalışılmaktadır. Uçaklarda kullanılan metalik malzemeler Faraday kafesi etkisi göstererek yıldırımdan kaynaklanan elektromanyetik alanların uçak içerisine girişine izin vermemektedir fakat günümüzde daha sık kullanılmaya başlayan kompozit yapılar bu konuda metallere kıyasla daha kötü performans göstermektedir. Ayrıca uçak üzerinde bulunan pencere, kapı gibi süreksizlikler Faraday kafesi üzerinde boşluklar yaratmakta ve elektromanyetik alanların uçak içerisine girişine olanak sağlamaktadır. Bu sebeple uçak üzerinde kullanılan ekipmanların yıldırımın dolaylı etkilerine karşı kalifiye olması gerekmektedir. Ekipmanları yıldırımın dolaylı etkilerine karşı korumada en sık tercih edilen metot kabloların kalkanlanmasıdır. Kalkanın koruma etkisini ve sonlandırma metotlarının bu korumaya katkısını anlamak oldukça önemlidir. Bu çalışmada, yıldırımın dolaylı etkisine karşı çeşitli kalkan sonlandırma teknikleri hem deneysel metotlarla hem de EMA3D programında yapılan benzetim çalışmaları ile incelenmiş ve 360˚ arka kabuk sonlandırma tekniğinin kullanılmasının yaklaşık 3 dB koruma sağlayarak oldukça etkili olduğu bulunmuştur. Deneylerden elde edilen sonuçlar benzetim sonuçları ve önceki çalışmalar ile karşılaştırılmış ve elde edilen sonuçların birbiri ile tutarlı olduğu görülmüştür. Lightning is a natural phenomenon where high voltages and currents suddenly discharge. It can be caused by clouds themselves, clouds between them, or clouds near the earth. Aircraft are also at risk of being struck by lightning and there is currently no way to prevent this from happening. Instead, efforts are being made to protect by reducing the effects of lightning. Metal structures in aircraft form a Faraday cage which helps in preventing lightning currents from entering the aircraft. However, composite structures, which are becoming more prevalent in the aviation sector, are less efficient in doing so compared to metals. Additionally, openings such as windows in the aircraft can break the Faraday cage and allow strong electromagnetic fields to penetrate. Hence, all equipment used on board the aircraft must be adequately qualified and lightning-proof. The most popular technique used to reduce the indirect effects of lightning on electronics is cable shielding. In this study, various shield termination techniques against the indirect effect of lightning were examined both by experimental methods and by simulation studies in the EMA3D program, and it was found that the use of 360˚ back shell termination technique was very effective by providing about 3 dB of protection. The results obtained from the experiments are compared with simulation results and previous studies and it has been observed that the obtained results are consistent with each other.
An OFDM throughput analysis for cognitive radio application in contiguous or noncontiguous TV white spaces
(2015) Ciftlikli, Cebrail; Tuncer, Ahmet Turgut; Ozturk, Yusuf
Radio frequency spectrum is a finite and scarce resource. Efficient use of the radio frequency spectrum is a fundamental research issue. Since a large portion of the assigned radio frequency spectrum is used only sporadically, the bands currently allocated to TV services can be opportunistically reassigned to support broadband networking services while continuing to provide broadcast TV. The fragmented and unused TV channels named white spaces have a considerable amount of bandwidth potential and long transmission ranges. Bandwidth scalability can be supported by bonding multiple contiguous or noncontiguous consecutive channels using orthogonal frequency division multiplexing (OFDM)-based cognitive radio. In this paper, an in-depth throughput analysis of OFDM fixed carrier spacing and fixed carrier number approaches has been done for various modulation schemes in TV white spaces. Signal propagation delay is studied under various channel conditions. An analytical model-based estimation of the throughput by taking into account channel bonding is presented.
A viable snore detection system: hardware and software implementations
(2020) Tuncer, Ahmet Turgut; Bilgen, Mehmet
A stand-alone, custom-made biomedical system was introduced for long-term monitoring of sleep and detection of snoring events. Commercially available electronic components were assembled for recording audio, pulse, and respiration signals. Its software was implemented for off-line processing of the acquired signals in C++ and MATLAB environments. The linear and nonlinear features of the signals were extracted and characterized using spectral energy distribution, entropy, and largest Lyapunov exponent (LLE). The performance of the system was evaluated with real physiological data gathered from 14 chronic snorers. Analysis of the cases indicated that the system identified the snoring events with an accuracy of 88.22%, sensitivity of 94.91%, and positive predictive value of 90.95%. This high level of validation confirmed the reliability and utility of the system in detecting snoring.