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Publication Open Access A 2D MEMS stage for optical applications(Society of Photo-optical Instrumentation Engineers (SPIE), 2006) Ataman, Çağlar; Petremand, Yves; Noell, Wilfried; Epitaux, Marc; de Rooij, Nico F.; Department of Electrical and Electronics Engineering; Ürey, Hakan; Faculty Member; Department of Electrical and Electronics Engineering; College of Engineering; 8579A 2D MEMS platform for a microlens scanner application is reported. The platform is fabricated on an SOI wafer with 50/μm thick device layer. Entire device is defined with a single etching step on the same layer. Through four S-shaped beams, the device is capable of producing nonlinear 2D motion from linear ID translation of two pairs of comb actuator sets. The device has a clear aperture of 2mm by 2mm, which is hallowed from the backside for micro-optics assembly. In this paper, a numerical device model and its validation via experimental characterization results are presented. Integration of the micro-optical components with the stage is also discussed. Additionally, a new driving scheme to minimize the settling time of the device in DC operation is explored.Publication Open Access A cartridge based sensor array platform for multiple coagulation measurements from plasma(Royal Society of Chemistry (RSC), 2015) Bulut, Serpil; Yaralioglu, G. G.; Department of Electrical and Electronics Engineering; Department of Molecular Biology and Genetics; Department of Chemical and Biological Engineering; Çakmak, Onur; Ermek, Erhan; Kılınç, Necmettin; Barış, İbrahim; Kavaklı, İbrahim Halil; Ürey, Hakan; PhD Student; Other; Researcher; Teaching Faculty; Faculty Member; Department of Electrical and Electronics Engineering; Department of Molecular Biology and Genetics; Department of Chemical and Biological Engineering; College of Engineering; Graduate School of Sciences and Engineering; College of Sciences; N/A; 109991; N/A; 111629; 40319; 8579This paper proposes a MEMS-based sensor array enabling multiple clot-time tests for plasma in one disposable microfluidic cartridge. The versatile LoC (Lab-on-Chip) platform technology is demonstrated here for real-time coagulation tests (activated Partial Thromboplastin Time (aPTT) and Prothrombin Time (PT)). The system has a reader unit and a disposable cartridge. The reader has no electrical connections to the cartridge. This enables simple and low-cost cartridge designs and avoids reliability problems associated with electrical connections. The cartridge consists of microfluidic channels and MEMS microcantilevers placed in each channel. The microcantilevers are made of electroplated nickel. They are actuated remotely using an external electro-coil and the read-out is also conducted remotely using a laser. The phase difference between the cantilever oscillation and the coil drive is monitored in real time. During coagulation, the viscosity of the blood plasma increases resulting in a change in the phase read-out. The proposed assay was tested on human and control plasma samples for PT and aPTT measurements. PT and aPTT measurements from control plasma samples are comparable with the manufacturer's datasheet and the commercial reference device. The measurement system has an overall 7.28% and 6.33% CV for PT and aPTT, respectively. For further implementation, the microfluidic channels of the cartridge were functionalized for PT and aPTT tests by drying specific reagents in each channel. Since simultaneous PT and aPTT measurements are needed in order to properly evaluate the coagulation system, one of the most prominent features of the proposed assay is enabling parallel measurement of different coagulation parameters. Additionally, the design of the cartridge and the read-out system as well as the obtained reproducible results with 10 mu l of the plasma samples suggest an opportunity for a possible point-of-care application.Publication Open Access A deep learning approach for data driven vocal tract area function estimation(Institute of Electrical and Electronics Engineers (IEEE), 2018) Department of Computer Engineering; Department of Electrical and Electronics Engineering; Erzin, Engin; Asadiabadi, Sasan; Faculty Member; Department of Computer Engineering; Department of Electrical and Electronics Engineering; College of Sciences; Graduate School of Sciences and Engineering; 34503; N/AIn this paper we present a data driven vocal tract area function (VTAF) estimation using Deep Neural Networks (DNN). We approach the VTAF estimation problem based on sequence to sequence learning neural networks, where regression over a sliding window is used to learn arbitrary non-linear one-to-many mapping from the input feature sequence to the target articulatory sequence. We propose two schemes for efficient estimation of the VTAF; (1) a direct estimation of the area function values and (2) an indirect estimation via predicting the vocal tract boundaries. We consider acoustic speech and phone sequence as two possible input modalities for the DNN estimators. Experimental evaluations are performed over a large data comprising acoustic and phonetic features with parallel articulatory information from the USC-TIMIT database. Our results show that the proposed direct and indirect schemes perform the VTAF estimation with mean absolute error (MAE) rates lower than 1.65 mm, where the direct estimation scheme is observed to perform better than the indirect scheme.Publication Open Access A fast, accurate, and separable method for fitting a Gaussian function(Institute of Electrical and Electronics Engineers (IEEE), 2019) Al-Nahhal Ibrahim; Dobre Octavia A.; Moloney Cecilia; Ikki Salama; Department of Electrical and Electronics Engineering; Başar, Ertuğrul; Faculty Member; Department of Electrical and Electronics Engineering; College of Engineering; 149116Publication Open Access A generalization of multiple-mode OFDM with index modulation(Institute of Electrical and Electronics Engineers (IEEE), 2018) Wen, Miaowen; Li, Qiang; Zhang, Wensong; Department of Electrical and Electronics Engineering; Başar, Ertuğrul; Faculty Member; Department of Electrical and Electronics Engineering; College of Engineering; 149116In this paper, we propose the scheme of generalized multiple-mode orthogonal frequency division multiplexing with index modulation (GMM-OFDM-IM), which allows a different subcarrier to utilize a signal constellation of a different size while conveying the same number of IM hits. Considering phase shift keying (PSK) constellations, we present design guidelines for GMM-OFDM-IM to achieve the optimal error performance in the asymptotically high signal-to-noise ratio region. A computationally efficient and near-optimal detector based on the idea of sequential decoding is also tailored to GMM-OFDM-IM to avoid the detection of an illegimate constellation permutation. Monte Carlo simulations are conducted to examine GNIM-OFDM-IM, whose inherent properties and advantages are revealed by the simulation results.Publication Open Access A hybrid architecture for federated and centralized learning(Institute of Electrical and Electronics Engineers (IEEE), 2022) Elbir, Ahmet M.; Papazafeiropoulos, Anastasios K.; Kourtessis, Pandelis; Chatzinotas, Symeon; Department of Electrical and Electronics Engineering; Ergen, Sinem Çöleri; Faculty Member; Department of Electrical and Electronics Engineering; College of Engineering; 7211Many of the machine learning tasks rely on centralized learning (CL), which requires the transmission of local datasets from the clients to a parameter server (PS) entailing huge communication overhead. To overcome this, federated learning (FL) has been suggested as a promising tool, wherein the clients send only the model updates to the PS instead of the whole dataset. However, FL demands powerful computational resources from the clients. In practice, not all the clients have sufficient computational resources to participate in training. To address this common scenario, we propose a more efficient approach called hybrid federated and centralized learning (HFCL), wherein only the clients with sufficient resources employ FL, while the remaining ones send their datasets to the PS, which computes the model on behalf of them. Then, the model parameters are aggregated at the PS. To improve the efficiency of dataset transmission, we propose two different techniques: i) increased computation-per-client and ii) sequential data transmission. Notably, the HFCL frameworks outperform FL with up to 20% improvement in the learning accuracy when only half of the clients perform FL while having 50% less communication overhead than CL since all the clients collaborate on the learning process with their datasets.Publication Open Access A lightning discharge producing a beam of relativistic electrons into space(American Geophysical Union (AGU), 2010) Cohen, M. B.; Said, R. K.; Briggs, M. S.; Fishman, G. J.; Connaughton, V.; Cummer, S. A.; Department of Electrical and Electronics Engineering; İnan, Umran Savaş; Faculty Member; Department of Electrical and Electronics Engineering; College of Engineering; 177880Strong electric fields associated with lightning generate brief (similar to 1 ms) but intense Terrestrial Gamma-ray Flashes (TGFs), detected by spacecrafts. A few events are thought to be the signature of a relativistic electron beam escaping the atmosphere, which is distinguishable from a TGF since the lightning discharge is along the geomagnetic field line from the spacecraft, rather than below. We refer to this event herein as a 'Terrestrial Energetic-electron Flash' (TEF), and present the first TEF with associated discharge. The TEF was detected by the Gamma-ray Burst Monitor aboard the Fermi satellite, and is correlated with a lightning discharge detected by three Stanford University AWESOME ELF/VLF receivers, a Duke University ULF receiver, and by the GLD360 lightning geolocation network. The discharge, nearly simultaneous with the generated electrons, was of intense peak current and of positive polarity, and with a modest total charge transfer, similar to TGF-associated discharges.Publication Open Access A low-SWaP, low-Cost transceiver for physically secure UAV communication with visible light(Springer, 2020) Department of Electrical and Electronics Engineering; Ergen, Sinem Çöleri; Soner, Burak; Faculty Member; Department of Electrical and Electronics Engineering; College of Engineering; Graduate School of Sciences and Engineering; 7211; N/AUnmanned aerial vehicles (UAV) are expected to utilize optical wireless technologies alongside radio frequency technologies for reliable, secure and high bandwidth communications. While terrestrial and atmospheric laser-based solutions in the past have achieved physically secure communication with very complex beam tracking/pointing mechanisms with large and costly telescopes, such systems are neither suitable nor necessary for medium-range (<100 m) commercial UAV communications. With the proliferation of low-cost solid-state lighting equipment and visible band photodetectors, visible light communications (VLC) offer a low-size-weight-and-power (SWaP) and low-cost solution. This paper presents a novel low-SWaP and low-cost transceiver for physically secure VLC in medium-range commercial UAV applications. Full implementation details for a proof-of-concept prototype built completely with off-the-shelf components are also reported.Publication Open Access A MEMS based visible-NIR Fourier transform microspectrometer - art. no. 61860C(Society of Photo-optical Instrumentation Engineers (SPIE), 2006) Wolter, A.; Department of Electrical and Electronics Engineering; Ataman, Çağlar; Ürey, Hakan; Işıkman, Serhan Ömer; PhD Student; Faculty Member; Department of Electrical and Electronics Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; 8579; N/ADesign, fabrication and characterization of a novel out-of-plane vertical comb-drive actuator based Fourier transform microspectrometer (FTS) is presented. The spectrometer utilizes resonant mode vertical comb actuators as a variable-depth diffraction grating and a single photodetector to monitor the 0th order of the diffraction pattern. The spectrum of the source illuminating the gratings is computed by Fourier transforming the 0th order intensity as a function of the optical path difference. The vertical comb actuators have a travel range of 100 mu m under atmospheric pressure with 28V excitation, which yields a theoretical spectral resolution of 0.5nm in the visible and better than 5nm in the telecom wavelengths.Publication Open Access A new RIS architecture with a single power amplifier: energy efficiency and error performance analysis(Institute of Electrical and Electronics Engineers (IEEE), 2022) Alexandropoulos, George C.; Department of Electrical and Electronics Engineering; Başar, Ertuğrul; Taşçı, Recep Akif; Kılınç, Fatih; Faculty Member; Master Student; Researcher; Department of Electrical and Electronics Engineering; Graduate School of Sciences and Engineering; College of Engineering; 149116; N/A; N/AMany electrochemical devices are based on the fundamental process of ion migration and accumulation on surfaces. Complex interplay of molecular properties of ions and device dimensions control the entire process and define the overall dynamics of the system. Particularly, for ionic liquid-based electrolytes it is often not clear which property, and to what extent, contributes to the overall performance of the device. Herein we use X-ray photoelectron spectroscopy (XPS) while the device is under electrical bias. Such a procedure reveals localized electrical potential developments, through binding energy shifts of the atomic core levels, in a chemically specific fashion. Combining it with square-wave AC modulation, the information can also be extended to time domain, and we investigate devices configured as a coplanar capacitor, with an ionic liquid as the electrolyte, in macro-dimensions. Our analysis reveals that a nonlinear voltage profile across the device emerges from spatially non-uniform electrical double layer formation on electrode surfaces. Interestingly the coplanar capacitor has an extremely slow time response which is particularly controlled by IL film thickness. XPS measurements can capture the ion dynamics in the tens of seconds to microseconds range, and reveal that ionic motion is all over the device, including on metallic electrode regions. This behavior can only be attributed to motion in more than one dimension. The ion dynamics can also be faithfully simulated by using a modified PNP equation, taking into account steric effects, and device dimensions. XPS measurements on two devices with different dimensions corroborated and validated the simulation results. The present results propose a new experimental approach and provide new insights into the dynamics of ions across electrochemical devices.