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Permanent URI for this collectionhttps://hdl.handle.net/20.500.14288/3
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Publication Metadata only Modeling and characterization of comb-actuated resonant microscanners(Iop Publishing Ltd, 2006) N/A; Department of Electrical and Electronics Engineering; Ataman, Çağlar; Ürey, Hakan; PhD Student; Faculty Member; Department of Electrical and Electronics Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; 8579The dynamics of the out-of-plane comb-drive actuator used in a torsional resonant mode microscanner is discussed. The microscanner is fabricated using the standard SOI technology by Fraunhofer, IPMS and utilized in various display, barcode scanning, spectroscopy and other imaging applications. The device is a parametrically excited system and exhibits hysteretic frequency response, nonlinear transient response, subharmonic oscillations, multiple parametric resonances, and alternating-oscillation-frequency behavior. Analytical and numerical models are developed to predict the parametric system dynamics. The analytical model is based on the solution of the linear Mathieu equation and valid for small angular displacements. The numerical model is valid for both small and large deflection angles. The analytical and numerical models are validated with the experimental results under various ambient pressures and excitation schemes and successfully predict the dynamics of the parametric nature of the microscanner. As many as four parametric resonances are observed at 30 mTorr. The models developed in this paper can be used to optimize the structure and the actuator.Publication Metadata only On heat transfer at microscale with implications for microactuator design(Iop Publishing Ltd, 2009) Yalçınkaya, Arda D.; Zervas, Michalis; Leblebici, Yusuf; N/A; Department of Mechanical Engineering; N/A; Özsun, Özgür; Alaca, Burhanettin Erdem; Yılmaz, Mehmet; Master Student; Faculty Member; Master Student; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; College of Engineering; Graduate School of Sciences and Engineering; N/A; 115108; N/AThe dominance of conduction and the negligible effect of gravity, and hence free convection, are verified in the case of microscale heat sources surrounded by air at atmospheric pressure. A list of temperature-dependent heat transfer coefficients is provided. In contrast to previous approaches based on free convection, supplied coefficients converge with increasing temperature. Instead of creating a new external function for the definition of boundary conditions via conductive heat transfer, convective thin film coefficients already embedded in commercial finite element software are utilized under a constant heat flux condition. This facilitates direct implementation of coefficients, i. e. the list supplied in this work can directly be plugged into commercial software. Finally, the following four-step methodology is proposed for modeling: (i) determination of the thermal time constant of a specific microactuator, (ii) determination of the boundary layer size corresponding to this time constant, (iii) extraction of the appropriate heat transfer coefficients from a list provided and (iv) application of these coefficients as boundary conditions in thermomechanical finite element simulations. An experimental procedure is established for the determination of the thermal time constant, the first step of the proposed methodology. Based on conduction, the proposed method provides a physically sound solution to heat transfer issues encountered in the modeling of thermal microactuators.Publication Metadata only A deformation-based approach to tuning of magnetic micromechanical resonators(2018) Yalçınkaya, Arda D.; Department of Mechanical Engineering; N/A; Department of Mechanical Engineering; Biçer, Mahmut; Esfahani, Mohammad Nasr; Alaca, Burhanettin Erdem; Researcher; PhD Student; Faculty Member; Department of Mechanical Engineering; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); College of Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; 115108Resonance frequency tuning in magnetic micromechanical resonators remains a primary field of study for frequency reference applications. The use of magnetic micromechanical resonators for innovative timing, oscillator and sensing applications necessitates a platform for the precise control of the resonance frequency. The present work addresses a deformation based technique for tuning the resonance frequency of nickel micromechanical resonators. Frequency response is measured through magnetic actuation and optical readout. The tuning approach is based on a combination of flexural deformation and uniaxial strain. The bending deformation is achieved by using a DC current through the microbeam. This magnetomotive mechanism reduces the resonance frequency by about 13% for a maximum DC current of 80 mA. A substrate bending method is used for applying uniaxial strain to increase the resonance frequency by about 8%. A bidirectional frequency modulation is thus demonstrated by utilizing both deformation techniques. The interpretation of results is carried out by finite element analysis and electromechanical analogy in an equivalent circuit. Using deformation techniques, this study provides a rigorous approach to control the resonance frequency of magnetic micromechanical resonators.Publication Metadata only Dynamics of spacing adjustment and recovery mechanisms of ABAC-type growth pattern in ternary eutectic systems(Elsevier, 2017) N/A; N/A; Department of Mechanical Engineering; Mohagheghi, Samira; Şerefoğlu, Melis; PhD Student; Researcher; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; College of Engineering; 329277; 44888In directionally solidified 2D samples at ternary eutectic compositions, the stable three-phase pattern is established to be lamellar structure with ABAC stacking, where A, B, and C are crystalline phases. Beyond the stability limits of the ABAC pattern, the system uses various spacing adjustment mechanisms to revert to the stable regime. In this study, the dynamics of spacing adjustment and recovery mechanisms of isotropic ABAC patterns were investigated using three-phase In-Bi-Sn alloy. Unidirectional solidification experiments were performed on 23.0 and 62.7 mu m-thick samples, where solidification front was monitored in real-time from both sides of the sample using a particular microscopy system. At these thicknesses, the pattern was found to be 2D during steady-state growth, i.e. both top and bottom microstructures were the same. However, during spacing adjustment and recovery mechanisms, 3D features were observed. Dynamics of two major instabilities, lamellae branching and elimination, were quantified. After these instabilities, two key ABAC pattern recovery mechanisms, namely, phase invasion and phase exchange processes, were identified and analyzed. After elimination, ABAC pattern is recovered by either continuous eliminations of all phases or by phase exchange. After branching, the recovery mechanisms are established to be phase invasion and phase exchange.Publication Metadata only FR4 laser scanner with dynamic focus(IEEE-Inst Electrical Electronics Engineers Inc, 2009) Sprague, Randy B.; N/A; Department of Electrical and Electronics Engineering; Işıkman, Serhan Ömer; Ürey, Hakan; Master Student; Faculty Member; Department of Electrical and Electronics Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; 8579An electromagnetically actuated optical scanner made using standard printed circuit board technology with integrated dynamic focusing feature is presented. Dynamic focus is achieved with an independently controlled plunger machined on the flame retardant-4 (FR4) platform. Integration of a laser diode and lens, torsional scanner, and the plunger for dynamic focus adjustment on FIN platform greatly improves the form factor of the device for imaging applications. A peak-to-peak mechanical scan angle of 50 degrees is achieved. The dynamic focus control allows for shifting the beam waist location from 80 mm up to 650 mm.Publication Metadata only Analysis of the knight shift data on Li and Zn substituted YBa2Cu3O6+x(Elsevier, 2001) Department of Physics; Bulut, Nejat; Faculty Member; Department of Physics; College of Sciences; N/AThe Knight shift data on Li and Zn substituted YBa2Cu3O6+x are analyzed using an itinerant model with short-range antiferromagnetic correlations. The model parameters, which are determined by fitting the experimental data on the transverse nuclear relaxation rate T-2(-1) of pure YBa2Cu3O6+x, are used to calculate the Knight shifts for various nuclei around a nonmagnetic impurity located in the CuO2 planes. The calculations are carried out for Li and Zn impurities substituted into optimally doped and underdoped YBa2Cu3O6+x. The results are compared with the Li-7 and Y-89 Knight shift measurements on these materials. (C) 2001 Elsevier Science B.V. All rights reserved.Publication Metadata only Monolithic technology for silicon nanowires in high-topography architectures(Elsevier, 2017) Wollschlager, Nicole; Rangelow, Ivo W.; Leblebici, Yusuf; Department of Mechanical Engineering; Esfahani, Mohammad Nasr; Yılmaz, Mustafa Akın; Alaca, Burhanettin Erdem; PhD Student; PhD Student; Faculty Member; Department of Mechanical Engineering; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; 115108Integration of silicon nanowires (Si NWs) in three-dimensional (3D) devices including integrated circuits (ICs) and microelectromechanical systems (MEMS) leads to enhanced functionality and performance in diverse applications. The immediate challenge to the extensive use of Si NWs in modern electronic devices is their integration with the higher-order architecture. Topography-related limits of integrating Si NWs in the third dimension are addressed in this work. Utilizing a well-tuned combination of etching and protection processes, Si NWs are batch-produced in bulk Si with an extreme trench depth of 40 gm, the highest trench depth obtained in a monolithic fashion within the same Si crystal so far. The implications of the technique for the thick silicon-on-insulator (S01) technology are investigated. The process is transferred to SOI wafers yielding Si NWs with a critical dimension of 100 nm along with a trench aspect ratio of 50. Electrical measurements verify the prospect of utilizing such suspended Si NWs spanning deep trenches as versatile active components in ICs and MEMS. Introducing a new monolithic approach to obtaining Si NWs and the surrounding higher-order architecture within the same SOI wafer, this work opens up new possibilities for modem sensors and power efficient ICs. (C) 2017 Elsevier B.V. All rights reserved.Publication Metadata only Bose-einstein condensate in a harmonic trap with an eccentric dimple potential(Institute of Physics (IOP) Publishing, 2008) Uncu, H.; Tarhan, D.; Demiralp, E.; Department of Physics; Müstecaplıoğlu, Özgür Esat; Faculty Member; Department of Physics; College of Sciences; 1674We investigate Bose-Einstein condensation of noninteracting gases in a harmonic trap with an offcenter dimple potential. We specifically consider the case of a tight and deep dimple potential, which is modeled by a point interaction. This point interaction is represented by a Dirac delta function. The atomic density, chemical potential, critical temperature and condensate fraction, and the role of the relative depth and the position of the dimple potential are analyzed by performing numerical calculations.Publication Metadata only Dynamic modeling of soft magnetic film actuated scanners(IEEE-Inst Electrical Electronics Engineers Inc, 2009) N/A; N/A; Department of Electrical and Electronics Engineering; Işıkman, Serhan Ömer; Ürey, Hakan; Master Student; Faculty Member; Department of Electrical and Electronics Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; 8579Dynamic behavior of magnetic thin film actuators is investigated in detail and applied to various laser scanning applications. Magnetic hysteresis effects are incorporated into the model developed in the prior work, which assumes linear magnetization as a function of magnetic field and is based on the distributed point-by-point calculation of the magnetostatic moments and forces across the film surface. A simple functional form is used to model the major B-H loop of ferromagnetic films. The model is validated with permalloy (Ni-Fe) plated polymer actuators. The actuators are excited using an external electro-coil and the structures deflect due to magnetic anisotropy torque. The ac deflection of the actuators is modeled by calculating the point-by-point moments on the magnetic film and the solution can handle nonuniform external field and unsaturated magnetic film cases. A 25 degrees optical scan angle is demonstrated for laser scanning display and imaging applications with a nonoptimum coil. Scaling the model to MEMS devices is also discussed.Publication Metadata only Piezoresistive silicon nanowire resonators as embedded building blocks in thick SOI(Iop Publishing Ltd, 2018) Karakan, M. Çağatay; Orhan, Ezgi; Hanay, M. Selim; Leblebici, Yusuf; N/A; N/A; Department of Mechanical Engineering; Esfahani, Mohammad Nasr; Kılınç, Yasin; Alaca, Burhanettin Erdem; PhD Student; PhD Student; Faculty Member; Department of Mechanical Engineering; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Graduate School of Sciences and Engineering; College of Engineering; College of Engineering; N/A; N/A; 115108The use of silicon nanowire resonators in nanoelectromechanical systems for new-generation sensing and communication devices faces integration challenges with higher-order structures. Monolithic and deterministic integration of such nanowires with the surrounding microscale architecture within the same thick crystal is a critical aspect for the improvement of throughput, reliability and device functionality. A monolithic and IC-compatible technology based on a tuned combination of etching and protection processes was recently introduced yielding silicon nanowires within a 10 mu m-thick device layer. Motivated by its success, the implications of the technology regarding the electromechanical resonance are studied within a particular setting, where the resonator is co-fabricated with all terminals and tuning electrodes. Frequency response is measured via piezoresistive readout with frequency down-mixing. Measurements indicate mechanical resonance with frequencies as high as 100 MHz exhibiting a Lorentzian behavior with proper transition to nonlinearity, while Allan deviation on the order of 3-8 ppm is achieved. Enabling the fabrication of silicon nanowires in thick silicon crystals using conventional semiconductor manufacturing, the present study thus demonstrates an alternative pathway to bottom-up and thin silicon-on-insulator approaches for silicon nanowire resonators.