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Permanent URI for this communityhttps://hdl.handle.net/20.500.14288/2
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Publication Metadata only Discrete and continuous mathematical models for torsional vibration of micromechanical scanners(Springer, 2007) Department of Electrical and Electronics Engineering; N/A; Department of Electrical and Electronics Engineering; Ürey, Hakan; Faculty Member; N/A; College of Engineering; N/A; 8579; N/AMicromechanical scanners are used in various industrial scanning applications like. display and imaging technologies. The desired vibration mode is often the torsional mode, so derivation of an accurate mathematical model for calculation of torsional mode frequency has great importance. In this work, discrete and continuous mathematical models are given for free torsional vibration of a box shaped scanner suspended with two beams. Numerical calculation of torsional rigidity using energy methods is shown. The derivations are extendible to scanners that have non-rectangular beam cross-sections, orthotropic material anisotropy, and different mirror geometries. Analytical formulas are compared with three-dimensional FEM simulations using ANSYS commercial software. The FEM simulations and analytical formulas are verified with experimental results. FEM simulations and experimental results showed that simple discrete models can be used for a wide range of beam dimensions except for the cases where beam inertia is comparable to mirror inertia.Publication Metadata only Measurement and characteristic analysis of ris-assisted wireless communication channels in sub-6 ghz outdoor scenarios(IEEE, 2023) Lan, Jifeng; Sang, Jian; Zhou, Mingyong; Gao, Boning; Meng, Shengguo; Li, Xiao; Tang, Wankai; Jin, Shi; Cheng, Qiang; Cuit, Tie Jun; Department of Electrical and Electronics Engineering; Department of Electrical and Electronics Engineering; Başar, Ertuğrul; College of EngineeringReconfigurable intelligent surface (RIS)-empowered communication has recently drawn significant attention due to its superior capability in manipulating the wireless propagation environment. However, the channel modeling and measurement of RIS-assisted wireless communication systems in real environment has not been adequately studied. In this paper, we construct a channel measurement system using vector network analyzer (VNA) is used to investigate RIS-assisted wireless communication channel in outdoor scenarios at 2.6 GHz. New path loss (PL) models including angle domain information are proposed by refining the traditional close-in (CI) and floating-intercept (FI) models. In the proposed models, both influences of the distance from transmitter (TX) to RIS and the distance from receiver (RX) to RIS on the PL, are taken into account. In addition, the value of root mean square (RMS) delay spread of RIS-assisted wireless communication is found to be much smaller than that of the traditional non line-of-sight (NLOS) case, implying that RIS provides a virtual line-of-sight (LOS) link.Publication Metadata only Measurement-based characterization of physical layer security for ris-assisted wireless systems(IEEE, 2023) Kesir, Samed; Wikelek, Ibrahim; Pusane, Ali Emre; Gorcin, Ali; Department of Electrical and Electronics Engineering; Department of Electrical and Electronics Engineering; Kayraklık, Sefa; Başar, Ertuğrul; CoreLab; Graduate School of Sciences and Engineering; College of EngineeringThere have been recently many studies demonstrating that the performance of wireless communication systems can be significantly improved by a reconfigurable intelligent surface (RIS), which is an attractive technology due to its low power requirement and low complexity. This paper presents a measurement-based characterization of RISs for providing physical layer security, where the transmitter (Alice), the intended user (Bob), and the eavesdropper (Eve) are deployed in an indoor environment. Each user is equipped with a software-defined radio connected to a horn antenna. The phase shifts of reflecting elements are software controlled to collaboratively determine the amount of received signal power at the locations of Bob and Eve in such a way that the secrecy capacity is aimed to be maximized. An iterative method is utilized to configure a Greenerwave RIS prototype consisting of 76 passive reflecting elements. Computer simulation and measurement results demonstrate that an RIS can be an effective tool to significantly increase the secrecy capacity between Bob and Eve.Publication Open Access MEMS scanners for display and imaging applications(Society of Photo-optical Instrumentation Engineers (SPIE), 2004) Department of Electrical and Electronics Engineering; Department of Electrical and Electronics Engineering; Ürey, Hakan; Faculty Member; College of Engineering; 8579Dynamic display and imaging applications demand high performance scanners, which has high frequency (exceeding 10KHz), large scan-angle-mirror-size product (>+/-10deg.mm), good optical surface quality (<lambda/20 static and dynamic flatness), high sensitivity position sensors, and high-torque actuators that are compact and low power. This paper discusses the resolution and other optical performance requirements for diffraction-limited and non-diffraction-limited light sources in a scanning system. A set of analytical formulas is presented for calculating the torsion and other four fundamental oscillation mode vibration frequencies. The formulas include the effects of material anisotropy in orthotropic materials, such as Silicon and effective mass and inertia of the flexures. The validity range of formulas are extended by introducing a correction factor based on flexure width and flexure length ratios. The formulas are very efficient for performance trades and optimization. For scanner actuation, we present two compact scanner actuation mechanisms: out-of-plane comb actuator and novel two-coil electromagnetic actuator.Publication Open Access Nonlinear frequency response of comb-driven microscanners(Society of Photo-optical Instrumentation Engineers (SPIE), 2004) Department of Electrical and Electronics Engineering; Department of Electrical and Electronics Engineering; Ataman, Çağlar; Ürey, Hakan; PhD Student; Faculty Member; Graduate School of Sciences and Engineering; College of Engineering; N/A; 8579Accurate prediction of the dynamic behavior of comb-driven MEMS microscanners is important to optimize the actuator and structure design. In this paper, a numerical and an analytical model for the dynamic analysis of comb-driven microscanners under different excitation schemes are presented. The numerical model is based on a second order nonlinear differential equation. Due to the nature of the torque function, this governing equation of motion is a parametric nonlinear ODE, which exhibits hysteretic frequency domain behavior and subharmonic oscillations. Experimental results and approximate analytical expressions for this nonlinear torque function of the comb-drive are presented. Amplitude and phase relationship between the excitation signal and the resultant oscillations at different excitation frequencies are measured and we show that they are in close agreement with the numerical simulations. Analytical model uses perturbation methods to reach approximate close-form expressions for the dynamic behavior of the device in the first parametric resonance region. It is also utilized to predict the stability regions on the frequency-excitation voltage plane, where the device exhibit hysterical characteristics. Analytical and numerical modeling approaches proposed in this paper provides a simple yet powerful way to analyze the nonlinear frequency response of comb-driven actuators and simplify the design process for a microscanner based system.Publication Metadata only Route to batch-compatible fabrication of nanotweezers by guided self-assembly(IEEE, 2007) Bøggild, Peter; Tang, P. Torben; Hansen, Ole; N/A; Department of Mechanical Engineering; Department of Electrical and Electronics Engineering; Department of Mechanical Engineering; Department of Electrical and Electronics Engineering; Şardan, Özlem; Alaca, Burhanettin Erdem; Yalçınkaya, Arda Deniz; Master Student; Faculty Member; Researcher; Graduate School of Sciences and Engineering; College of Engineering; College of Engineering; N/A; 115108; 144523Fabrication of integrated micro and nanoscale components in a single batch is one of the biggest challenges for nanosystems developement. A self-assembly technique that enables "batch-compatible" integration of micro electro mechanical systems with nanoribbons is presented by demonstrating electrostatically actuated combdrive microgrippers with nanoribbon end-effectors. Preliminary fabrication results demonstrate the possibility of obtaining well defined spatial density and orientation of nanoribbons matching the precision of top-down techniques and at the same time allowing complete alignment and registry with subsequent lithography steps.