141
Arşivlenen Tez
1
DOI Atanmış
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Departman Tezleri
Yarı rezonans yapı ve yayılmış tayf metodu ile indüksiyon ocak tasarımı ve deneysel sonuçları
This thesis presents an induction cooker design and its detailed experimental results. The design is based on Quasi Resonant Topology and is unique in terms of the particular Jitter Method it employs to drive the semiconductor switches (IGBTs).Most induction cookers are based on Half Bridge Topology. Although Quasi Resonant Topology offers a more cost effective implementation, it introduces more EMI problems. However, we solve these problems with our Jitter Method. Although there are other works in the literature that solve the EMI issues by some sort of jitter methods (i.e., spread spectrum methods), these methods do not address the high voltage stress created across the IGBTs. However, the Jitter Method proposed in this thesis also reduces collector-emitter voltage stress besides improving EMI. Note that jitter methods also prevent mechanical vibration (i.e., resonance), which cause audible noise.Another thing that makes this thesis unique in the literature is the rich set of experimental results it contains ? based on an experimental prototype we built with a power rating of 2300W. While the existing literature mostly contains theoretical treatment, we have produced detailed experimental results for Quasi Resonant Topology and show that the current harmonics (drawn from the utility) stay within the published standards (TS EN 61000-3-2). We also include experimental results for Delivered Power Detection, Pan Detection, and Protection Circuits.
ALTO servisli eş görevli ağlarda gerçek zamanlı ölçeklenebilir video akıtımı
It has been measured that, as high as 80% of the average Internet traffic is now from peer-to-peer (P2P) applications, and upwards of 90% during peak hours. These results tell us that a significant portion of the traffic that ISPs route is P2P traffic. However, since the typical P2P application overlay network model is network-oblivious, due to its nature, it causes inefficient network utilization, and low qualityof experience, from the perspective of the network providers and the end users, respectively. This inefficient resource utilization increases inter-ISP traffic, and leads to serious disruptions on ISP economics as well as lower QoE by the users.A significant portion of the P2P traffic on the Internet is for video applications. Furthermore, real networks are heterogeneous in link rates. Thus a live video streamingservice should support streams with different qualities for users using different data rates. A possible solution to this problem is achieved by creating a different video file for each quality level. However, this solution is inefficient due to data duplication.To improve ISP economics, improve network efficiency and achieve acceptable QoE performance, we implement a P2P Live Scalable Video Streaming Mechanism and Application Layer Traffic Optimization (ALTO) Server, by using different peer ranking algorithms in this thesis. The main objective of this thesis, to show that the ALTO protocol reduces the inter-ISP traffic significantly while maintaining the application performance. Results reveal that, placing an ALTO Server decreases the inter-ISP traffic dramatically while maintaining a satisfactory QoE performance for the streaming video application.
Kenar bulma algoritması ve regresyon ile dct-tabanlı referanssız bloklanma ölçüm metodu
This thesis presents a blocking artifact detection algorithm and consists of detailed experimental results. Blocking artifacts are a serious problem in low data rate transmission of such videos (or image sequences), which employ DCT-based compression algorithms. Too much compression due to bandwidth constraints can introduce blocking artifacts. Online quality measurement techniques for artifacts such as blockiness are required to for broadcasters and internet service providers to inspect their streaming systems. Blockiness measurement can be done through full-reference (FR), reduced-reference (RR), or no-reference (NR) methods. NR is the most efficient one as accessing reference content may not be always possible. NR methods also offer the possibility of real-time inspection. We propose a novel NR blockiness measurement method. The method is based on DCT and uses a model of the human visual system like some of the literature. However, it is unique as it uses Sobel edge detection algorithm to avoid miscalculations and also employs regression analysis to match mean opinion scores (MOS) of human observers. These unique features of our method let us achieve results that are more correlated to the MOS for LIVE dataset, which is used to train and test our algorithm. To measure how well our results match the MOS values in LIVE, we use Pearson and Spearman correlation formulations. The best Spearman correlation obtained in the literature for LIVE dataset is 94% while we get 95%. On the other hand, we get a Pearson correlation of 98% and surpass the best in the literature by 94%.
Çok kullanıcılı optik kablosuz haberleşme sistemlerinin başarım analizi
Terrestrial Free Space Optical (FSO) communications involve using optical beams to carry information through atmospheric channels between two points. Unlike radio frequency (RF) communications, FSO systems are not burdened by spectrum licensing or interference to/from other systems. These systems are also easy-to-install and redeployable, therefore considered a powerful alternative to fiber optic or RF systems, particularly, for the purpose of "last mile" problem. In addition, the nature of point to point transmission by means of laser beam provides high immunity to interference and jamming from external sources. In the first chapter of the thesis, we provide an overview of FSO technology discussing the advantages and bottlenecks as well as mitigation techniques in FSO systems to overcome atmospheric turbulence induced fading problem. In the second chapter, we consider a multiuser FSO system over log-normal atmospheric turbulence channels. We investigate the outage probability of proposed system with various scheduling techniques including Round Robin, Opportunistic Round Robin, Select-Max and mth Best User Selection. We also verify the validity of the obtained closed-form expressions for outage probabilities through Monte Carlo simulations. In the third chapter, we extend the multiuser scenario to a parallel multihop (cooperative) FSO system and study its outage probability with the so-called mth Best Path Selection (m-BPS) protocol. Specifically, we consider an FSO communication system which employs M parallel relaying paths each of which consists of N decode-and-forward relays. In this protocol, data is transmitted through the mth (m ≥2) best path towards the destination since the best path (i.e., m=1) might not be available due to scheduling or load balancing issues. After expressing closed-form of outage capacity, we derive the diversity order of proposed system. In the last chapter, we derive outage capacity and throughput expressions for the multiuser FSO system under consideration. These expressions are obtained under the assumption of both independent identical and non-identical distributions assuming log-normal channel model and then confirmed through simulation results.
Dairesel cmut için çökme modu eşdeğer devre modeli
Capacitive micromachined ultrasonic transducer is a microelectromechanical device, which serves as an acoustic signal source or sensor, in a variety of applications including medical ultrasound imaging, ultrasound therapy, airborne applications. It has a suspended membrane with an electrode inside, and at the underlying substrate there is another electrode, so that the membrane can be deflected by the electrical field formed between the electrodes. Similarly, any mechanical disturbance on the membrane can be sensed as a change in the capacitance of the two electrodes. CMUT is a nonlinear device which has a distributed mechanical operation. Although, it is a mass-spring system basically, the nonlinear electrical force and the radiation force makes it impossible to solve CMUT through analytical equations. In order to predict its behavior, and design a CMUT towards the needs of a specific application, either finite element analysis or equivalent electrical circuit modeling should be utilized. Finite element analysis (FEA) can predict the distributed CMUT operation with high accuracy, but its usage is limited to designs employing low number of CMUTs because of the computation cost. Recently, advances in equivalent circuit modeling, made it possible to simulate arrays employing very high number of CMUTs, with high accuracy. These models assume uncollapsed mode operation and except collapsed mode operation as it is highly nonlinear. This thesis focuses on obtaining an accurate equivalent circuit model for a circular CMUT in collapsed mode. The outcome is a parametric circuit model, that can simulate a CMUT of any physical and material parameters, under an arbitrary electrical or mechanical excitation. In collapsed mode, the compliance of the membrane is no longer constant as in uncollapsed mode, and it increases with increasing contact radius. Similarly, the capacitance, the electrical force and the radiation impedance all have new behavior regarding the contact radius. As there is no analytical solution for those parameters, we perform numerical calculations and extract expressions for each of them. First, we calculate the collapsed membrane deflection, utilizing the exact electrical force distribution in the analytical formulation of membrane deflection. Then we use the deflection profile to calculate the capacitance, electrical force, and compliance. Performing a set of calculations for different CMUT dimensions, different pressure and voltage levels, we obtain dependencies of those parameters on rms deflection. Then we develop a lumped element model of collapsed membrane operation, expressing the parameters as functions of rms deflection. The radiation impedance for the collapsed mode is also included in the model. The model is then merged with the uncollapsed mode model to obtain a simulation tool that handles all CMUT behavior, in transmit or receive. Large- and small-signal operation of a single CMUT can be fully simulated for any excitation regime. The results are in good agreement with FEM simulations.
Kapasitif mikro-işlenmiş ultrasonik çeviricilerde düzgün olmayan zarlar
ABSTRACT NONUNIFORM MEMBRANES IN CAPACITIVE MICROMACHINED ULTRASONIC TRANSDUCERS Muhammed N. Şenlik M.S. in Electrical and Electronics Engineering Supervisor: Prof. Dr. Abdullah Atalar January 28, 2005 Capacitive micromachined ultrasonic transducers (cMUT) are used to receive and transmit ultrasonic signals. The device is constructed from many small, in the order of microns, circular membranes, which are connected in parallel. When they are immersed in water, the bandwidth of the cMUT is limited by the mem brane's second resonance frequency, which causes an increase in the mechanical impedance of the membrane. In this thesis, we propose a new membrane shape to shift the second resonance frequency to higher values, in addition to keeping the impedance of the membrane as small as possible. The structure consists of a very thin membrane with a rigid mass at the center. The stiffness of the central region moves the second resonance to a higher frequency. This membrane configuration is shown to work better compared to conventionally used uniform membranes during both reception and transmission. The improvement in the bandwidth is more than %30 with an increase in the gain. Keywords: Capacitive micromachined ultrasonic transducer, cMUT, nonuniform membrane. IV
Insansız hava araçları için eşanlı konumlandırma ve haritalama
Most mobile robot applications require the robot to be able to localize itself in anunknown environment without prior information so that the robot can navigate andaccomplish tasks. The robot must be able to build a map of the unknown environmentwhile simultaneously localizing itself in this environment. The Simultaneous Localizationand Mapping (SLAM) is the formulation of this problem which has drawn aconsiderable amount of interest in robotics research for the past two decades. Thiswork focuses on the SLAM problem for single and multiple agents equipped with visionsensors. We develop a vision-based 2-D SLAM algorithm for single and multipleUnmanned Aerial Vehicles (UAV) flying at constant altitude. Using the features ofimages obtained from an on-board camera to identify different landmarks, we applydifferent approaches based on the Extended Kalman Filter (EKF), the InformationFilter (IF) and the Particle Filter (PF) to the SLAM problem. We present some simulationresults and provide a comparison between the different implementations. Wefind Particle Filter implementations to perform better in estimations when comparedto EKF and IF, however EKF and IF present more consistent results.Keywords: UAV, SLAM, Extended Kalman Filter, Information Filter, Particle Filter,FastSLAM, SIFT, multi-agent systems.
Optik çoğuşma ağlarındaki TCP trafikleri için sıkışıklık penceresi tabanlı uyarlamalı çoğuşma oluşturma algoritması
Burst assembly is one of the key factors affecting the TCP performance in Optical Burst Switching (OBS) networks. Timer based burst assembly algorithm generates bursts independent of the rate of TCP flows. When TCP congestion window is small, the fixed-delay burst assembler waits unnecessarily long, which increases the end-to-end delay and decreases the TCP goodput. On the other hand, when TCP congestion window becomes larger, the fixed-delay burst assembler may unnecessarily generate a large number of small-sized bursts, which increases the overhead and decreases the correlation gain, resulting in a reduction in the TCP goodput. Using simulations, we show that the usage of the congestion window (cwnd) size of TCP flows in the burst assembly algorithm consistently improves the TCP goodput (by up to 38.4%) compared with the fixed-delay timer based assembly even when the timer based assembler uses the optimum assembly period threshold value. One limitation of this proposed method is the assumption that the exact value of the congestion window is available at the burst assembler. We then extend the adaptive burstification algorithm such that the burst assembler uses estimated values of the congestion window that are obtained via passive measurements at the ingress node. It is shown through simulations that even when estimated values are used, TCP goodput can achieve values close to the results obtained by using exact values of the congestion window.
Dairesel sonlu engel üzerinde geniş bant geniş hüzme açıklıklı piston tipi akustik dönüştürücü tasarımı
The design of a high power piezoelectric underwater transducer operating at frequency range 42 kHz-78 kHz with acoustic power capability in excess of 250W is described. The transducer consists of two back-to-back elements. Each element is formed by stacked PZT-4 ceramic rings, a matching and a steel backing layer, and placed in a finite rigid circular baffle. We investigate the dependence of bandwidth and beamwidth to the combination of piston and baffle radii, a and b, respectively. With ka of 2.45 (k is the wave number) at resonance and a b/a ratio of 2, the transducer resonates at 60kHz with 60% bandwidth and has a beamwidth of 60º at each half space. We show that when two transducers are placed at right angles spatially and driven in parallel, we can obtain an omnidirectional beam pattern in the lower frequency band. The beam pattern exhibits two dips in each quadrant at the higher end of the frequency band, which are within 8 dB. We also investigate power handling capability of the transducer from thermal point of view using finite element analysis. The input impedance measurements agree well with the numerical results within the pass band.
Gürbüz minimum-maksimum kestiricinin kalman filtresine uyarlanması
Kalman filtering is one of the most essential tools in estimating an unknown state of a dynamic system from measured data, where the measurements and the previous states have a known relation with the present state. It has generally two steps, prediction and update. This filtering method yields the minimum mean-square error when the noise in the system is Gaussian and the best linear estimate when the noise is arbitrary. But, Kalman filtering performance degrades significantly with the model uncertainty in the state dynamics or observations. In this thesis, we consider the problem of estimating an unknown vector x in a state-space model that may be subject to uncertainties. We assume that the model uncertainty has a known bound and we seek a robust linear estimator for x that minimizes the worst case mean-square error across all possible values of x and all possible values of the model matrix. Robust minimax estimation technique is derived and analyzed in this thesis, then applied to the state-space model and simulation results with different noise perturbation models are presented. Also, a radar tracking application assuming a linear state dynamics is also investigated.Modifications to the James-Stein estimator are made according to the scheme we develop in this thesis, so that some of its limitations are dealt with. In our scheme, James-Stein estimation can be applied even if the observation equation is perturbed and the number of observations are less than the number of states, still yielding robust estimations.