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Publication Metadata only A communication theoretical modeling of single-layer graphene photodetectors and efficient multireceiver diversity combining(Ieee-Inst Electrical Electronics Engineers Inc, 2012) N/A; Department of Electrical and Electronics Engineering; Gülbahar, Burhan; Akan, Özgür Barış; PhD Student; Faculty Member; Department of Electrical and Electronics Engineering; Graduate School of Sciences and Engineering; College of Engineering; 234525; 6647Graphene with groundbreaking properties has tremendous impact on physical sciences as 2-D atomic layer carbon sheet. Its unique electronic and photonic properties lead to applications such as transistors, graphene photodetectors (GPDs), and electronic circuit components. Metal-graphene-metal (MGM) GPDs with single-or multilayer graphene sheets are promising for future nanoscale optical communication architectures because of wide range absorption from far infrared to visible spectrum, fast carrier velocity, and advanced production techniques due to planar geometry. In this paper, signal-to-noise ratio (SNR), bit-error rate (BER), and data rate performances of nanoscale single-layer symmetric MGM photodetectors are analyzed for intensity modulation and direct detection (IM/DD) modulation. Shot and thermal noise limited (NL) performances are analyzed emphasizing graphene layer width dependence and domination of thermal NL characteristics for practical power levels. Tens of Gbit/s data rates are shown to be achievable with very low BERs for single-receiver (SR) GPDs. Furthermore, multireceiver (MR) GPDs and parallel line-scan (PLS) network topology are defined improving the efficiency of symmetric GPDs. SNR performance of SR PLS channels are both improved and homogenized with MR devices having the same total graphene area by optimizing their positions with maxmin solutions and using maximal ratio and equal gain diversity combining techniques.Publication Metadata only A communication theoretical modeling of single-walled carbon nanotube optical nanoreceivers and broadcast power allocation(Ieee-Inst Electrical Electronics Engineers Inc, 2012) N/A; Department of Electrical and Electronics Engineering; Gülbahar, Burhan; Akan, Özgür Barış; PhD Student; Faculty Member; Department of Electrical and Electronics Engineering; Graduate School of Sciences and Engineering; College of Engineering; 234525; 6647Carbon nanotube (CNT) with its ground-breaking properties is a promising candidate for future nanoscale communication networks. CNTs can be used as on-chip optical antenna for wireless interconnects. Carbon nanotube field-effect transistors (CNTFETs) show significant performance as photodetectors due to wide spectral region and tunable bandgap. In this paper, CNTFETs composed of semiconducting single-walled carbon nanotube (SWNT) and metal contacts (M-SWNT-M) are used as photodiode receivers in nanoscale optical communication by theoretically modeling diameter-dependent characteristics for shot-, dark-, and thermal-noise-limited cases. Bit error rate (BER), cutoff bit rate, and signal-to-noise ratio performance are analyzed for intensity modulation and direct detection modulation. The multireceiver CNT nanoscale network topology is presented for information broadcast and the minimum SNR is maximized solving NP-hard max-min power allocation problem with semidefinite programming relaxation and branch and bound framework. The significant performance improvement is observed compared with uniform power allocation. Derived model is compared with existing experiments and hundreds of Mb/s data rate is achievable with very low BERs. Furthermore, optimization gain is highest for thermal-noise-limited case while the shot-noise-limited case gives the highest data rate.Publication Metadata only A magnetically actuated resonant mass sensor with integrated optical readout(Ieee-Inst Electrical Electronics Engineers Inc, 2008) N/A; N/A; Department of Electrical and Electronics Engineering; N/A; Department of Electrical and Electronics Engineering; Department of Chemical and Biological Engineering; Department of Mechanical Engineering; Öztürk, Alibey; Ocaklı, Hüseyin İlker; Özber, Natali; Ürey, Hakan; Kavaklı, İbrahim Halil; Alaca, Burhanettin Erdem; Master Student; Researcher; Master Student; Faculty Member; Faculty Member; Faculty Member; Department of Electrical and Electronics Engineering; Department of Chemical and Biological Engineering; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; College of Engineering; Graduate School of Sciences and Engineering; College of Engineering; College of Engineering; College of Engineering; N/A; N/A; N/A; 8579; 40319; 115108Nickel cantilevers with integrated diffraction gratings are used as resonant mass sensors with a resolution of 500 femtograms. Their applicability to biosensing is demonstrated with human opioid receptors. The device is fabricated through a single-mask lithographic process. The microoptical readout provides a simple measurement platform with one external photodiode. Thanks to its ac operation principle, the device is immune to environmental noise and entails a high tolerance to fabrication defects. Obtained signal-to-noise ratio is comparable to that of a high-end Doppler vibrometer. The device with these aspects for systems integration and microarray technology is a candidate for low-cost portable sensors.Publication Metadata only An efficient and low-latency deep inertial odometer for smartphone positioning(IEEE-Inst Electrical Electronics Engineers Inc, 2021) Abdel-Qader, A.; N/A; Department of Electrical and Electronics Engineering; Soyer, Muhammet Serhat; Onbaşlı, Mehmet Cengiz; Master Student; Faculty Member; Department of Electrical and Electronics Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; 258783The Global Positioning System (GPS) is not an effective solution for pedestrian indoor navigation using embedded devices because of poor signal penetration and high power requirements. Indoor positioning based purely on commercial-grade inertial measurement units (IMUs) may provide a good alternative but their significant noise and random bias must be eliminated. Although Kalman filters and pedestrian dead reckoning helped reduce the errors using IMUs, these methods cannot prevent the divergence of estimated position error. Deep learning was proposed for accurate position estimation with IMUs. Despite the progress, robust position estimation in mobile embedded devices using deep learning has not been established yet because of memory requirements, latency and inaccurate position estimation especially for stationary pedestrians. In this study, we present an efficient embedded deep learning approach for robust, real-time and accurate pedestrian position estimation using commercial Android smartphone IMUs. We first extended a publicly available deep inertial navigation dataset (OxIOD) with stationary data to enhance the positioning accuracy for both steady state and motion. Next, we trained and tested a deep learning architecture that yields a higher positioning accuracy with 50% lower network latency and 31% lower network size compared with earlier deep positioning networks such as IONet. Our real-time tests of the model in an Android smartphone indicated that the extension for the dataset reduces the position shift when the smartphone is stationary. Since our embedded deep learning solution simultaneously decreases the positioning error, latency and memory requirements, the solution paves the way for numerous practical indoor navigation applications.Publication Open Access Band alignment engineers faradaic and capacitive photostimulation of neurons without surface modification(American Physical Society (APS), 2019) Department of Electrical and Electronics Engineering; N/A; Department of Chemical and Biological Engineering; Department of Molecular Biology and Genetics; Srivastava, Shashi Bhushan; Melikov, Rustamzhon; Aria, Mohammad Mohammadi; Dikbaş, Uğur Meriç; Kavaklı, İbrahim Halil; Nizamoğlu, Sedat; Researcher; PhD Student; Master Student; Faculty Member; Faculty Member; Department of Electrical and Electronics Engineering; Department of Chemical and Biological Engineering; Department of Molecular Biology and Genetics; College of Engineering; Graduate School of Sciences and Engineering; College of Sciences; N/A; N/A; N/A; N/A; 40319; 130295Photovoltaic substrates have attracted significant attention for neural photostimulation. The control of the Faradaic and capacitive (non-Faradaic) charge transfer mechanisms by these substrates are critical for safe and effective neural photostimulation. We demonstrate that the intermediate layer can directly control the strength of the capacitive and Faradaic processes under physiological conditions. To resolve the Faradaic and capacitive stimulations, we enhance photogenerated charge density levels by incorporating PbS quantum dots into a poly(3-hexylthiophene-2,5-diyl):([6,6]-Phenyl-C61-butyric acid methyl ester (P3HT:PCBM) blend. This enhancement stems from the simultaneous increase of absorption, well matched band alignment of PbS quantum dots with P3HT:PCBM, and smaller intermixed phase-separated domains with better homogeneity and roughness of the blend. These improvements lead to the photostimulation of neurons at a low light intensity level of 1 mW cm(-2), which is within the retinal irradiance level. These findings open up an alternative approach toward superior neural prosthesis.Publication Open Access Biocompatible quantum funnels for neural photostimulation(American Chemical Society (ACS), 2019) N/A; Department of Chemical and Biological Engineering; N/A; Department of Electrical and Electronics Engineering; Department of Molecular Biology and Genetics; N/A; Jalali, Houman Bahmani; Doğru-Yüksel, Itır Bakış; Eren, Güncem Özgün; Nizamoğlu, Sedat; Karatüm, Onuralp; Melikov, Rustamzhon; Dikbaş, Uğur Meriç; Kavaklı, İbrahim Halil; Sadeghi, Sadra; Yıldız, Erdost; Ergün, Çağla; Şahin, Afsun; PhD Student; Faculty Member; PhD Student; Master Student; Faculty Member; PhD Student; PhD Student; Faculty Member; Department of Chemical and Biological Engineering; Department of Electrical and Electronics Engineering; Department of Molecular Biology and Genetics; Koç University Research Center for Translational Medicine (KUTTAM) / Koç Üniversitesi Translasyonel Tıp Araştırma Merkezi (KUTTAM); Graduate School of Sciences and Engineering; College of Engineering; College of Sciences; School of Medicine; N/A; N/A; N/A; 130295; N/A; N/A; N/A; 40319; N/A; N/A; N/A; 171267Neural photostimulation has high potential to understand the working principles of complex neural networks and develop novel therapeutic methods for neurological disorders. A key issue in the light-induced cell stimulation is the efficient conversion of light to bioelectrical stimuli. In photosynthetic systems developed in millions of years by nature, the absorbed energy by the photoabsorbers is transported via nonradiative energy transfer to the reaction centers. Inspired by these systems, neural interfaces based on biocompatible quantum funnels are developed that direct the photogenerated charge carriers toward the bionanojunction for effective photostimulation. Funnels are constructed with indium-based rainbow quantum dots that are assembled in a graded energy profile. Implementation of a quantum funnel enhances the generated photoelectrochemical current 215% per unit absorbance in comparison with ungraded energy profile in a wireless and free-standing mode and facilitates optical neuromodulation of a single cell. This study indicates that the control of charge transport at nanoscale can lead to unconventional and effective neural interfaces.Publication Open Access Broadband longwave radio remote sensing instrumentation(American Institute of Physics (AIP) Publishing, 2018) Cohen, Morris B.; Said, Ryan K.; McCormick, Jackson C.; Gross, Nicholas C.; Thompson, Lee; Higginson-Rollins, Marc; Chang, Jeffrey; Department of Electrical and Electronics Engineering; İnan, Umran Savaş; Faculty Member; Department of Electrical and Electronics Engineering; College of Engineering; 177880We present the performance characteristics of a high-sensitivity radio receiver for the frequency band 0.5-470 kHz, known as the Low Frequency Atmospheric Weather Electromagnetic System for Observation, Modeling, and Education, or LF AWESOME. The receiver is an upgraded version of the VLF AWESOME, completed in 2004, which provided high sensitivity broadband radio measurements of natural lightning emissions, transmitting beacons, and radio emissions from the near-Earth space environment. It has been deployed at many locations worldwide and used as the basis for dozens of scientific studies. We present here a significant upgrade to the AWESOME, in which the frequency range has been extended to include the LF and part of the medium frequency (MF) bands, the sensitivity improved by 10-25 dB to be as low as 0.03 fT/root Hz, depending on the frequency, and timing error reduced to 15-20 ns range. The expanded capabilities allow detection of radio atmospherics from lightning strokes at global distances and multiple traverses around the world. It also allows monitoring of transmitting beacons in the LF/MF band at thousands of km distance. We detail the specification of the LF AWESOME and demonstrate a number of scientific applications. We also describe and characterize a new algorithm for minimum shift keying demodulation for VLF/LF transmitters for ionospheric remote sensing applications.Publication Open Access Bulk-heterojunction photocapacitors with high open-circuit voltage for low light intensity photostimulation of neurons(Royal Society of Chemistry (RSC), 2021) Department of Electrical and Electronics Engineering; Department of Molecular Biology and Genetics; N/A; Department of Chemical and Biological Engineering; N/A; Srivastava, Shashi Bhushan; Melikov, Rustamzhon; Yıldız, Erdost; Dikbaş, Uğur Meriç; Sadeghi, Sadra; Kavaklı, İbrahim Halil; Şahin, Afsun; Nizamoğlu, Sedat; Researcher; PhD Student; PhD Student; Master Student; PhD Student; Faculty Member; Faculty Member; Faculty Member; Department of Electrical and Electronics Engineering; Department of Molecular Biology and Genetics; Department of Chemical and Biological Engineering; Koç University Research Center for Translational Medicine (KUTTAM) / Koç Üniversitesi Translasyonel Tıp Araştırma Merkezi (KUTTAM); Graduate School of Sciences and Engineering; College of Engineering; College of Sciences; School of Medicine; N/A; N/A; N/A; N/A; N/A; 40319; 171267; 130295High-level transduction control of light to bioelectricity is an important goal for the realization of superior neuron-device interfaces that can be used for regulating fundamental cellular processes to cure neurological disorders. In this study, a single-junction, wireless, and capacitive-charge-injecting optoelectronic biointerface with negligible faradaic reactions by using a high open-circuit voltage (0.75 V) bulk heterojunction of PTB7-Th:PC71BM is designed and demonstrated. The biointerface generates a 2-fold higher photocurrent in comparison with P3HT:PC61BM having an open-circuit voltage of 0.55 V. Furthermore, we observed that light intensity is logarithmically correlated with the open-circuit voltage of solar cells, and the photovoltage of the biointerfaces varies the switching speed of capacitive charge-transfer. Finally, pulse trains of capacitive stimuli at a low light intensity of 20 mW cm−2elicit action potential generation in primary hippocampal neurons extracted from E15-E17 Wistar Albino rats. These findings show the great promise of high open-circuit voltage bulk heterojunction biointerfaces for non-genetic, all-optical and safe modulation of neurons.Publication Open Access Cascadable direct current driven skyrmion logic inverter gate(American Physical Society (APS), 2022) Katmış, Ferhat; Department of Electrical and Electronics Engineering; Onbaşlı, Mehmet Cengiz; Cheghabouri, Arash Mousavi; Faculty Member; Department of Electrical and Electronics Engineering; College of Engineering; Graduate School of Sciences and Engineering; 258783; N/ANanoscale skyrmions enable ultralow-power nonvolatile logic gate designs due to their current-driven motion and topological protection. A key building block in skyrmion-based digital spintronics is the logic inverter (NOT) gate. Despite recent computational and practical demonstrations, a skyrmion-based low-power, wideband, and cascadable inverter gate is still a long way off. For skyrmion-based logic circuits, a systematic design and analysis of an inverter gate is essential. Here we present a skyrmion logic inverter design and analyze its full operation using micromagnetic modeling. Because of the substrate thermal conductivity, our investigations reveal that the all-metallic inverter gate can function with direct current drive, wide bandwidth, submicron footprint, no or low external magnetic field, cascadability, and with room-temperature thermal stability despite Joule heating. Using magnetic insulators for eliminating Joule heating and lowering the exchange stiffness, magnetic moment and other factors might further assist in reducing power consumption by more than four orders of magnitude.Publication Metadata only Comb-actuated resonant torsional microscanner with mechanical amplification(IEEE-Inst Electrical Electronics Engineers Inc, 2010) Brown, Dean; Davis, Wyatt O.; Department of Electrical and Electronics Engineering; Department of Electrical and Electronics Engineering; N/A; Department of Electrical and Electronics Engineering; Arslan, Aslıhan; Holmstrom, Sven; Gökçe, Sertan Kutal; Ürey, Hakan; Researcher; Researcher; Master Student; Faculty Member; Department of Electrical and Electronics Engineering; College of Engineering; College of Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; N/A; 8579A comb-actuated torsional microscanner is developed for high-resolution laser-scanning display systems. Typical torsional comb-drive scanners have fingers placed around the perimeter of the scanning mirror. In contrast, the structure in this paper uses cascaded frames, where the comb fingers are placed on an outer drive frame, and the motion is transferred to the inner mirror frame with a mechanical gain. The structure works only in resonant mode without requiring any offset in the comb fingers, keeping the silicon-on-insulator-based process quite simple. The design intent is to improve actuator efficiency by removing the high-drag fingers from the high-velocity scanning mirror. Placing them on the lower velocity drive frame reduces their contribution to the damping torque. Furthermore, placement on the drive frame allows an increase of the number of fingers and their capacity to impart torque. The microscanner exhibits a parametric response, and as such, the maximum deflection is found when actuated at twice its natural frequency. Analytical formulas are given for the coupled-mode equations and frame deflections. A simple formula is derived for the mechanical-gain factor. For a 1-mm x 1.5-mm oblong scanning mirror, a 76. total optical scan angle is achieved at 21.8 kHz with 196-V peak-to-peak excitation voltages. [2009-0304]