Graduate School of Engineering and Science

Permanent URI for this collectionhttps://hdl.handle.net/11693/115678

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Open Access
2-18 GHZ MMIC distributed amplifiers
(1994) Ergun, Sanlı
Using GaAs Monolithic Microwave Integrated Circuit (MMIC) technology three distributed amplifiers are realized. Two of these amplifiers employ single gate FETs and operate in the 2-18 GHz frequency range. They have 4.5 and 6.5 dB gain, respectively. The third amplifier utilizes cascode connected FETs. This amplifier operates in the 2-20 GHz range and has a gain of ~10 dB. All the three amplifiers have input and output return losses better than 10 dB. The isolation of the amplifiers with single gate FETs is better than 20 dB, whereas the cascode connection improves the isolation over 30 dB. The amplifiers are designed for a 50O-svstem. The simulations are made linearly, and the results match the theoretical work. In the design of these amplifiers a more detailed method is used in which the artificial transmission lines are investigated and optimized in their frequency behaviour. Besides, to realize these amplifiers, a new parametrized cell library for GEC-Marconi’s F20 foundry process is created and utilized.
Open Access
2-fold structures and homotopy theory
(2023-01) Haderi, Redi
It is well-known that correspondences between categories, also known as profunctors, serve in classifying functors. More precisely, every functor F : X → A straightens into a lax mapping χF : A → Catprof from A into a 2-category of categories and profunctors ([45]). We give a conceptual treatment of this fact from the lens of double category theory, contending the latter to be most natural environment to express this result. Then we venture into the world of simplicial sets and prove an analogous theorem. The notion of correspondence is easy to extend to simplicial sets, but a suitable double category may not be formed due to the lack of a natural tensor product. Nonetheless, we show that there is a natural simplicial category structure once we invoke higher correspondences. In proving our result we extend some notions from double category theory into the world of simplicial categories. As an application we obtain a realization of Lurie’s prediction that inner fibrations are classified by mappings into a higher category of correspondences between ∞-categories.
Open Access
3-dimensional median-based algorithms in image sequence processing
(1990) Alp, Münire Bilge
This thesis introduces new 3-dimensional median-based algorithms to be used in two of the main research areas in image sequence proc(',ssi,ng; image sequence enhancement and image sequence coding. Two new nonlinear filters are developed in the field of image sequence enhancement. The motion performances and the output statistics of these filters are evaluated. The simulations show that the filters improve the image quality to a large extent compared to other examples from the literature. The second field addressed is image sequence coding. A new 3-dimensional median-based coding and decoding method is developed for stationary images with the aim of good slow motion performance. All the algorithms developed are simulated on real image sequences using a video sequencer.
Open Access
33 Femtosecond Yb-doped optical frequency comb for frequency metrology applications
(2013) Şenel, Çağrı
Optical frequency combs have enabled many applications (high precision spectroscopy, table-top optical frequency metrology, optical atomic clocks, etc.), received considerable attention and a Nobel Prize. In this thesis, the development of a stabilized Yb-doped femtosecond optical frequency comb is presented. As a starting point in the development of the frequency comb, a new type of fiber laser has been designed using numerical simulations and realized experimentally. The developed laser is able to produce pulses that can be compressed to 33 fs without higher-order dispersion compensation. After realization of the laser, a new type of fiber amplifier has been developed to be used for supercontinuum generation. The amplifier produces 6.8 nJ pulses that can be compressed to 36 fs without higher-order dispersion compensation. The dynamics of supercontinuum generation have been studied by developing a separate simulation program which solves the generalized nonlinear Schr¨odinger equation. Using the simulation results, appropriate photonic crystal fiber was chosen and octave-spanning supercontinuum was generated. Carrier-envelope-offset frequency of the laser has been obtained by building an f-2f interferometer. Repetition rate and carrier-envelope offset frequency of the laser have been locked to Cs atomic clock using electronic feedback circuits, resulting in a fully stabilized optical frequency comb. The noise performance and stability of the system have been characterized. Absolute frequency measurement of an Nd:YAG laser, which was stabilized using iodine gas, has been performed using the developed optical frequency comb.
Open Access
3D dynamic modeling of spherical wheeled self-balancing mobile robot
(2012) İnal, Ali Nail
In recent years, dynamically stable platforms that move on spherical wheels, also known as BallBots, gained popularity in the robotics literature as an alternative locomotion method to statically stable wheeled mobile robots. In contrast to wheeled platforms which do not have to explicitly be concerned about their balance, BallBot platforms must be informed about their dynamics and actively try to maintain balance. Up until now, such platforms have been approximated by simple planar models, with extensions to three dimensions through the combination of decoupled models in orthogonal sagittal planes. However, even though capturing certain aspects of the robot’s motion is possible with such decoupled models, they cannot represent inherently spatial aspects of motion such as yaw rotation or coupled inertial effects due to the motion of the rigid body. In this thesis, we introduce a novel, fully-coupled 3D model for such spherical wheeled balancing platforms. We show that our novel model captures important spatial aspects of motion that have previously not been captured by planar models. Moreover, our new model provides a better basis for controllers that are informed by more expressive system dynamics. In order to establish the expressivity and accuracy of this new model, we present simulation studies in dynamically rich situations. We use circular paths to reveal the advantages of the new model for fast maneuvers. Additionally, we introduce new inverse-dynamics controllers for a better attitude control and investigate within simulations the capability of sustaining dynamic behaviors. We study the relation between circular motions in attitude angles and associated motions in positional variables for BallBot locomotion.
Open Access
3D electron density estimation in the ionosphere by using IRI-Plas model and GPS measurements
(2016-05) Tuna, Hakan
Three dimensional imaging of the electron density distribution in the ionosphere is a crucial task for investigating the ionospheric effects. Dual-frequency Global Positioning System (GPS) satellite signals can be used to estimate the Slant Total Electron Content (STEC) along the propagation path between a GPS satellite and ground based receiver station. However, the estimated GPS-STEC are very sparse and highly non-uniformly distributed for obtaining reliable 3D electron density distributions derived from the measurements alone. Standard tomographic re- construction techniques are not accurate or reliable enough to represent the full complexity of variable ionosphere. On the other hand, model based electron density distributions are produced according to the general trends of the iono- sphere, and these distributions do not agree with measurements, especially for geomagnetically active hours. In this thesis, a novel regional 3D electron density distribution reconstruction technique, namely IONOLAB-CIT, is proposed to as- similate GPS-STEC into physical ionospheric models. The IONOLAB-CIT is based on an iterative optimization framework that tracks the deviations from the ionospheric model in terms of F2 layer critical frequency and maximum ionization height resulting from the comparison of International Reference Ionosphere ex- tended to Plasmasphere (IRI-Plas) model generated STEC and GPS-STEC. The IONOLAB-CIT is applied successfully for the reconstruction of electron den- sity distributions over Turkey, during calm and disturbed hours of ionosphere using Turkish National Permanent GPS Network (TNPGN-Active). Reconstruc- tions are also validated by predicting the STEC measurements that are left out in the reconstruction phase. The IONOLAB-CIT is compared with the real ionosonde measurements over Greece, and it is shown that the IONOLAB-CIT results are in good compliance with the ionosonde measurements. The results of the IONOLAB-CIT technique are also tracked and smoothed in time by using Kalman filtering methods for increasing the robustness of the results.
Open Access
A 3D garment design and simulation system
(2004) Durupınar, Funda
In this thesis study, a 3D graphics environment for virtual garment design and simulation is presented. The proposed system enables the three dimensional construction of a garment from its two dimensional cloth panels, for which the underlying structure is a mass-spring model. Construction of the garment is performed through cutting, boundary smoothing , seaming and scaling. Afterwards, it is possible to do fitting on virtual mannequins like in the real life as if in a tailor’s workshop. The behavior of cloth under different environmental conditions is implemented applying a physically-based approach. As well as the simulation of the draping of garments, efficient and realistic visualization of garments is an important issue in cloth modelling. There are various material types and reflectance properties for fabrics. We have implemented a number of material and rendering options such as knitwear, woven cloth and standard shading methods such as Gouraud shading. Performance results of the system are presented at the end.
Open Access
3D hair design and key frame animation in real time
(2008) Başarankut, Barkın
Computer generated animations of humans, animals and all other kinds of objects have been studied extensively during the last two decades. The key for creating good animations has been to correctly imitate the behaviors of real objects and reflect these into computer generated images. With the rapid development of computer technology, creating realistic simulations has become possible, and the most striking components of these realistic animations happen to be the most dynamic (moving) parts; hair, in the case of human animations. With the development of high quality hair animations, the concern is not only creating physically correct animations, but also controlling these animations. An implementation of a key frame hair animation creation system, supported by a hair design tool, helping to model and animate hair easily, and provide these functionalities in real time is the aim of the proposed system. This work reviews several hair animation and sketching techniques, and proposes a system that provides a complete level of control (capable of controlling even the individual hair strands) of key frame animation and hair design in real time.
Open Access
3D hair sketching for real-time hair modeling and dynamic simulations
(2008) Aras, Rıfat
Hair has been an active research area in computer graphics society for over a decade. Different approaches have been proposed for different aspects of hair research such as modeling, simulating, animating and rendering. In this thesis, we introduce a sketch-based tool making use of direct manipulation interfaces to create hair models and furthermore simulate the created hair models under physically based constraints in real-time. Throughout the thesis, the created tool will be analyzed with respect to different aspects of the problem such as hair modeling, hair simulation, hair sketching and hair rendering.
Open Access
3D mesh animation system targeted for multi-touch environments
(2009) Ceylan, Duygu
Fast developments in computer technology have given rise to different application areas such as multimedia, computer games, and Virtual Reality. All these application areas are based on animation of 3D models of real world objects. For this purpose, many tools have been developed to enable computer modeling and animation. Yet, most of these tools require a certain amount of experience about geometric modeling and animation principles, which creates a handicap for inexperienced users. This thesis introduces a solution to this problem by presenting a mesh animation system targeted specially for novice users. The main approach is based on one of the fundamental model representation concepts, Laplacian framework, which is successfully used in model editing applications. The solution presented perceives a model as a combination of smaller salient parts and uses the Laplacian framework to allow these parts to be manipulated simultaneously to produce a sense of movement. The interaction techniques developed enable users to carry manipulation and global transformation actions at the same time to create more pleasing results. Furthermore, the approach utilizes the multi-touch screen technology and direct manipulation principles to increase the usability of the system. The methods described are experimented by creating simple animations with several 3D models; which demonstrates the advantages of the proposed solution.
Open Access
3D model compression using image compression based methods
(2007) Köse, Kıvanç
A Connectivity-Guided AdaptiveWavelet Transform (CGAWT) based mesh compres- sion algorithm is proposed. On the contrary to previous work, the proposed method uses 2D image processing tools for compressing the mesh models. The 3D models are ¯rst transformed to 2D images on a regular grid structure by performing orthogonal projections onto the image plane. This operation is computationally simpler than pa- rameterization. The neighborhood concept in projection images is di®erent from 2D images because two connected vertex can be projected to isolated pixels. Connectiv- ity data of the 3D model de¯nes the interpixel correlations in the projection image. Thus the wavelet transforms used in image processing do not give good results on this representation. CGAWT is de¯ned to take advantage of interpixel correlations in the image-like representation. Using the proposed transform the pixels in the detail subbands are predicted from their connected neighbors in the low-pass subbands of the wavelet transform. The resulting wavelet data is encoded using either \Set Parti- tioning In Hierarchical Trees" (SPIHT) or JPEG2000. SPIHT approach is progressive because di®erent resolutions of the mesh can be reconstructed from di®erent partitions of SPIHT bitstream. On the other hand, JPEG2000 approach is a single rate coder. The quantization of the wavelet coe±cients determines the quality of the reconstructed model in JPEG2000 approach. Simulations using di®erent basis functions show that lazy wavelet basis gives better results. The results are improved using the CGAWT with lazy wavelet ¯lterbanks. SPIHT based algorithm is observed to be superior to JPEG2000 based mesh coder and MPEG-3DGC in rate-distortion.
Open Access
3D reconstruction of point clouds using multi-view orthographic projections
(2006) Topçu, Osman
A method to reconstruct 3D point clouds using multi-view orthographic projections is examined. Point clouds are generated by means of a stochastic process. This stochastic process is designed to generate point clouds that mimic microcalcification formation in breast tissue. Point clouds are generated using a Gibbs sampler algorithm. Orthographic projections of point clouds from any desired orientation are generated. Volumetric intersection method is employed to perform the reconstruction from these orthographic projections. The reconstruction may yield erroneous reconstructed points. The types of these erroneous points are analyzed along with their causes and a performance measure based on linear combination is devised. Experiments have been designed to investigate the effect of the number of projections and the number of points to the performance of reconstruction. Increasing the number of projections and decreasing the number of points resulted in better reconstructions that are more similar to the original point clouds. However, it is observed that reconstructions do not improve considerably upon increasing the number of projections after some number. This method of reconstruction serves well to find locations of original points.
Open Access
5G PDSCH: performance analysis of DMRS and PTRS designs for channel and phase noise estimation in MM-WAVE
(2021-08) Pekcan, Doğan Kutay
The mm-Wave is one of the main enablers for the performance requirements of 5G. Although it provides communication systems with huge bandwidth and data rates, it also has some disadvantages as the carrier frequencies can significantly exceed 6 GHz and go up to 300 GHz. For example, there are significant challenges such as propagation loss and severe phase noise (PN). The PN can be observed in two parts: common phase error (CPE) and inter-carrier interference (ICI). In the literature, there are algorithms for the estimation and compensation of PN for OFDM-based systems. We apply both CPE and ICI compensation algorithms for 5G PDSCH at the carrier frequency of 70 GHz. Detailed performance analysis is performed for demodulation reference signal (DMRS) based channel estimation and phase-tracking reference signal (PTRS) based PN estimation. We observe the effects of different reference signal parameters in 5G for each PN compensation algorithm. For this purpose, we use up-to-date power spectral density (PSD) models for PN modeling and show uncoded bit error rate (BER) graphs obtained via extensive simulations for MATLAB's tapped delay line (TDL) channels. We also analyze the system performance under very high Doppler, where PTRS based channel estimation is compared with DMRS based channel estimation.
Open Access
A 600W on-coil Class-E RF power amplifier array with dynamic phase control for 3T MRI
(2022-09) Arslan, Abdullah Erkam
Due to their size and cooling constraints, conventional Magnetic Resonance Imaging (MRI) places radio frequency (RF) amplifiers away from the scanner. These RF amplifiers have relatively low efficiency due to the matching of 50Ω output impedance for means of transmission with cables. Switching Class-E amplifiers on the other hand, by default need a bare RLC network as their load and thus can be directly integrated with the bare unmatched coils and reduce the cost and power losses significantly. This thesis aims to build up on the previous theses’ line of work including [1, 2, 3, 4, 5]. Instead of mitigating the symptoms, chronic problems of artifacts have been fixed by focusing on their root causes in the FPGA side of the updated design.The driver has been updated, timing problems have been resolved. FPGA design is also extended to support multichannel phase control. A dual channel imaging configuration of on-coil Class-E amplifiers with on-the-fly digital fine phase control is presented for 3T MRI. The system can control the phase with less than 2° granularity (this setting can be fine-tuned down to 0.15°). Without any mechanical intervention with the coil setup, using merely phase control, illuminated slice depth is modulated to three times its base-size during scantime. B1 field maps are also extracted for another setup. Periodically linear switching (PLS) circuit model of the Class-E amplifier is derived and computed, yielding a simulator with fast and customizable optimization capability. The PLS model is also verified by SPICE and theoretical analysis.
Open Access
A 94-GHz phase inverter-variable gain amplifier in SiGe BiCMOS
(2017-07) Aydoğan, Yiğit
Phased array radar systems are capable of steering the beam of radio waves electronically by adjusting the gain and phase of each antenna element as desired. In order to achieve that, each element has to have gain/phase control and these parameters have to be controlled separately. In W-Band designs, constant gain- 360 phase control is di cult to achieve due to parasitic e ects of high frequencies which may quickly di er across di erent settings. Dividing the phase control task into di erent blocks in system eases the design di culties. A well developed WBand technology SiGe BiCMOS is also crucial to achieve high frequencies and system control. In this thesis, a 94-GHz SiGe BiCMOS phase inverter with variable gain ampli- er is developed. Single bit-180 phase inversion enables to use multiple bit-180 phase shifter which is easier to design in W-Band. In addition to that, variable gain ampli er allows to use this circuit in phased array systems for amplitude tapering to achieve desired beam forming.
Open Access
A bacterial living therapeutics with engineered protein secretion circuits to eliminate breast cancer cells
(2024-01) Binte Shahid, Gozeel
Cancer therapy often faces limitations due to potential side effects, prompting scientific interest in bacteria-based living cancer treatments. Yet, the complete utilization of bacteria in therapeutic applications confronts engineering hurdles. This thesis focuses on introducing a novel bacterial mechanism specifically intended to target and eliminate breast cancer cells. Our innovative approach involves modifying Escherichia coli (E. coli) to secrete a Shiga toxin called HlyE, a pore-forming protein that binds to HER2 receptors found on breast cancer cells. This binding process is facilitated by a nanobody expressed on the bacterial surface through the Ag43 autotransporter protein system. Our research demonstrates the effective binding of the nanobody to HER2+ cells in laboratory conditions (in vitro). Utilizing the YebF secretion system, we successfully leverage the secretion of HlyE, leading to the eradication of the targeted cancer cells. These outcomes emphasize the significant potential of our engineered bacteria as an innovative and promising strategy for breast cancer treatment. This pioneering approach represents a groundbreaking development in the field of cancer therapeutics. By harnessing the unique properties of bacteria and utilizing advanced engineering techniques, we've succeeded in creating a targeted and potent system capable of attacking breast cancer cells specifically marked by the HER2 receptor. Our study lays a robust foundation for future exploration and development in the realm of bacterial-based cancer therapies, offering potential solutions to the challenges encountered in traditional cancer treatment methods.
Open Access
A car following model with an attention-based cognitive framework: theory, application, and statistical analysis
(2024-08) Habboush, Seymanur Al
Traffic simulators are essential for testing autonomous driving algorithms, and they require driver models that accurately emulate human behavior to reflect real traffic conditions. This thesis focuses on developing human driver models to be used in these simulators. The limitations of fixed driver models, which do not adapt to new information, are addressed by introducing an attention-based learning mechanism inspired by human memory. This mechanism is integrated into a multi-type car-following model developed in this study. Unlike existing models, this approach allows the ego driver’s decisions to be influenced by both the vehicle in front and the driver behind them. The predictive capabilities of the proposed model is demonstrated using human driving data and a comprehensive statistical analysis of the model parameter distributions is provided. This analysis shows how the model captures general behavioral tendencies across different data sets, enhancing the understanding of interactions between human drivers and providing more realistic simulations for testing purposes. Finally, a step by step guide for using the model in the development of high-fidelity traffic models is presented.
Embargo
A coherent coupling between graphene plasmon and molecular vibration in strong coupling regime
(2024-08) Hossain, Md Faysal
Manipulating the energy states of atoms or molecules is of great interest due to its unlimited potential in spectroscopy, analytical chemistry, atomic structural analysis, imaging, chemical and biological sensing, and many other fields of micro-nanotechnology. Various ways of atomic or molecular energy modulation have been employed to date, such as electric or magnetic field excitation, molecular vibrational or rotational excitation, quantum tunneling, and laser excitation. When electromagnetic wave interacts with materials, it may fall into either a weak, i.e., Fano resonance and Purcell effect, or strong coupling regime depending on the coupling strength. The formation of hybridized polaritonic states in the strong coupling regime opens up a new way to modify materials' physical and chemical properties by altering energy levels of the material excitation. While the formation of polaritonic states has been demonstrated for excitonic transitions, the same phenomenon can also take place with molecular vibrations. In general, a Fabry-Pérot (FP) cavity having two parallel metal or dielectric mirrors is used to induce strong coupling as a cavity optical mode interacts with molecular vibrations of a material placed in the cavity. However, a planar optical cavity has a limited spatial resolution for monitoring polaritonic states. Moreover, strong coupling in the FP cavity represents an ensemble-average due to spatially-varied optical fields inside the FP cavity. To address some of the limitations of the FP cavity, I used a deep metal grating as a new optical resonator to demonstrate vibrational strong coupling (VSC). First, I simulated the optical properties of the deep metal grating and found that the hybridization between localized surface plasmon resonances and magnetic polaritons is responsible for generating strong mid-infrared optical resonances. When single-layer graphene was integrated into the grating, the grating resonances showed Fano line shapes as a result of a weak coupling between discrete graphene plasmon modes and continuum grating resonances. In addition, with the addition of a molecular absorber to the deep metal grating, VSC was achieved with tunability in polaritonic energy states by changing the system parameters including the grating height and widths, as well as the chemical potential applied to the graphene. In parallel with simulations, I generated a large area of double-layer graphene by chemical vapor deposition and fabricated deep metal grating structures by electron-beam lithography and inductively-coupled plasma etching.
Open Access
A comprehensive analysis of GaN HEMTs: electro-mechanical behavior, defect generation, and drain LAG reduction with HfO2 layers
(2023-07) Güneş, Burak
Gallium Nitride High Electron Mobility Transistors (GaN HEMTs) have rapidly emerged as a transformative technology, owing to the unique properties of the substrate material. They are poised to become a revolutionary advancement in RF amplifier applications, primarily due to their capability to operate at high frequencies and power levels with superior efficiency compared to conventional devices. Despite the rapid progressions, a noticeable gap persists in the literature regarding the relation-ship between mechanical stresses, defect generation, and their subsequent impact on the electrical characteristics of AlGaN/GaN HEMTs. Moreover, current dispersion effects, which are trapping induced reductions in output power, continues to remain a pressing issue. To address these limitations, this study first adopts a multifaceted approach and integrates mechanical simulations and Raman spectroscopy, in order to resolve fine details of stress distributions that a diffraction-limited Raman probe cannot resolve. This enables an extensive modeling of stresses in a typical HEMT structure and helps elucidate the underlying dynamics of defect generation, with the ultimate goal of informing and guiding the development of advanced fabrication techniques. In a second study, an ultrathin blanket dielectric deposition approach was devised to alleviate surface trapping, and consequently, mitigate current dispersion. The proposed streamlined fabrication process yielded a substantial improvement in device performance without compromising the transistor transfer characteristics.
Embargo
A decomposable branch-and-price formulation for optimal classification trees
(2024-07) Yöner, Elif Rana
Construction of Optimal Classification Trees (OCTs) using mixed-integer programs, is a promising approach as it returns a tree with minimum classification error. Yet solving integer programs to optimality is known to be computationally costly, especially as the size of the instance and the depth of the tree grow, calling for efficient solution methods. Our research presents a new, decomposable model which lends itself to efficient solution algorithms such as Branch-and-Price. We model the classification tree using a “patternbased” formulation, deciding which feature should be used to split data at each branching node of each leaf. Our results are promising, illustrating the potential of decomposition in the domain of binary OCTs.