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Permanent URI for this collectionhttps://hdl.handle.net/20.500.14288/3
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Publication Metadata only IDE-integrated microneedle arrays as fully biodegradable platforms for wearable/implantable capacitive biosensing(Institute of Electrical and Electronics Engineers Inc., 2023) Department of Electrical and Electronics Engineering; Ürey, Hakan; Mirzajani, Hadi; Department of Electrical and Electronics Engineering; Koç University Research Center for Translational Medicine (KUTTAM) / Koç Üniversitesi Translasyonel Tıp Araştırma Merkezi (KUTTAM); College of EngineeringMicroneedle biosensors have emerged as a promising tool for in situ biomarker detection due to their minimally invasive nature and ability to interface with interstitial fluid (ISF). However, most previously demonstrated ones are limited to in situ detection of small molecules and ions, employing amperometry or potentiometry measurement techniques with electrical current or voltage output metrics, respectively, which may not be suitable for detecting large molecules, such as proteins. This letter presents an innovative approach utilizing a microneedle array integrated with an interdigitated electrode (MAIDE), enabling in situ capacitive detection and quantification of protein biomarkers. Following microneedle penetration, the interdigitated electrode array establishes direct contact with the solution, enabling real-time monitoring of interfacial capacitance modulations as the result of the binding reaction, leading to the acquisition of rich molecular data. Equivalent circuit model extraction followed by impedance spectroscopy for different concentrations of bovine serum albumin (BSA) indicated the suitability of the proposed platform in tracking the interfacial capacitance variations with respect to different BSA concentrations of 100, 10, and 1 μg/mL with a detection limit of 21 ng/mL. Furthermore, the device showed satisfactory results for biodegradability experiments where it disintegrated for a duration of 10 h. In addition, in vivo experiments show stable capacitance readings with (dC/C)% deviations less than 0.5%, indicating its potential for biodegradable wearable/implantable capacitive biosensing applicationsPublication Metadata only Machine learning-based PHY-authentication without prior attacker information for wireless multiple access channels(Springer, 2024) Department of Electrical and Electronics Engineering; Altun, Ufuk; Başar, Ertuğrul; Department of Electrical and Electronics Engineering; Graduate School of Sciences and Engineering; College of EngineeringPhysical layer (PHY) authentication methods provide spatial security by exploiting the unique channel between two users. In recent years, many studies focused on substituting traditional threshold-based detection mechanisms with machine/deep learning classifiers to solve the threshold selection problem and obtain better detection accuracy. However, these studies assume that receivers have access to spoofer's channel information at the training of the classifier, which is unrealistic for real-time scenarios. In this study, we propose a PHY-authentication architecture for wireless multiple access channels (W-MACs) that removes this assumption and works without any prior information about the spoofer. The proposed method is designed for multi-user systems and is suitable for any classifier model or communication protocol. The feasibility and the performance of the proposed method are investigated via computer simulations and compared with a benchmark model. The results proved the feasibility of the proposed method as it can detect spoofers successfully without requiring spoofers' channel information.Publication Metadata only On the performance of OFDM-IM systems in the presence of CFO effects(Elsevier Inc., 2024) Besseghier, Mokhtar; Ghouali, Samir; Djebbar, Ahmed Bouzidi; Department of Electrical and Electronics Engineering; Başar, Ertuğrul; Department of Electrical and Electronics Engineering; ; College of Engineering;This study presents a comprehensive analysis of the performance degradation effects of carrier frequency offset (CFO) on orthogonal frequency division multiplexing with index modulation (OFDM-IM) systems operating over frequency-selective multipath fading channels. CFO is an impairing factor that degrades the signal-to-noise ratio (SNR) through signal attenuation and inter-carrier interference (ICI). We derive a closed-form expression to quantify the SNR degradation under CFO for OFDM-IM systems. Additionally, we formulate a very tight upper bound for the bit error rate (BER), accounting for index modulation errors, CFO distortion, and multipath fading. The presented analytical formulations capture the unique characteristics of OFDM-IM systems and facilitate precise performance evaluation. The findings yield valuable insights into mitigating CFO-induced BER degradation through appropriate system parameter selection and CFO compensation techniques. Moreover, this investigation makes significant contributions towards designing reliable OFDM-IM communication links resilient to the combined effects of index modulation, frequency offsets, and dispersive channel conditions.Publication Metadata only An audio-driven dancing avatar(Springer, 2008) Balci, Koray; Kizoglu, Idil; Akarun, Lale; Canton-Ferrer, Cristian; Tilmanne, Joelle; Bozkurt, Elif; Erdem, A. Tanju; Department of Computer Engineering; N/A; N/A; Department of Computer Engineering; Department of Electrical and Electronics Engineering; Yemez, Yücel; Ofli, Ferda; Demir, Yasemin; Erzin, Engin; Tekalp, Ahmet Murat; Faculty Member; PhD Student; Master Student; Faculty Member; Faculty Member; Department of Computer Engineering; Department of Electrical and Electronics Engineering; College of Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; College of Engineering; 107907; N/A; N/A; 34503; 26207We present a framework for training and synthesis of an audio-driven dancing avatar. The avatar is trained for a given musical genre using the multicamera video recordings of a dance performance. The video is analyzed to capture the time-varying posture of the dancer's body whereas the musical audio signal is processed to extract the beat information. We consider two different marker-based schemes for the motion capture problem. The first scheme uses 3D joint positions to represent the body motion whereas the second uses joint angles. Body movements of the dancer are characterized by a set of recurring semantic motion patterns, i.e., dance figures. Each dance figure is modeled in a supervised manner with a set of HMM (Hidden Markov Model) structures and the associated beat frequency. In the synthesis phase, an audio signal of unknown musical type is first classified, within a time interval, into one of the genres that have been learnt in the analysis phase, based on mel frequency cepstral coefficients (MFCC). The motion parameters of the corresponding dance figures are then synthesized via the trained HMM structures in synchrony with the audio signal based on the estimated tempo information. Finally, the generated motion parameters, either the joint angles or the 3D joint positions of the body, are animated along with the musical audio using two different animation tools that we have developed. Experimental results demonstrate the effectiveness of the proposed framework.Publication Metadata only Characterization of finite photonic crystals with defects(Institute of Electrical and Electronics Engineers (IEEE), 2011) N/A; Department of Electrical and Electronics Engineering; Karabulut, Emine Pınar; Aksun, M. İrşadi; Reseacher; Faculty Member; Department of Electrical and Electronics Engineering; College of Engineering; College of Engineering; N/A; 28358A simple computational approach is proposed to obtain the dispersion characteristics that could be observed outside of general finite-extent photonic crystals with defects. Since introducing and tailoring defects in photonic crystals are crucial for designing practical devices, the proposed method may play an important role in characterization and optimization of such defects. The method uses reflection data, due to an incident plane wave at a given frequency, collected at the front interface of a photonic crystal. It is simple and applicable for general photonic crystals, that is, photonic crystals with any periodicity, 1D, 2D, and 3D, and even with any kind of defects. The validity of the method was tested and verified on 1D and 2D finite photonic crystals, for which the reflection coefficient data at the front interface can be easily obtained by analytical means and numerical simulations, respectively. In addition, different types of defects, like random and periodic defects, were studied and it has been shown that the method is capable of providing information pertinent to the outside world on the defect modes.Publication Metadata only Noma-based downlink relaying with media -based modulation(Elsevier, 2020) Can, Mehmet; Altunbaş, İbrahim; Department of Electrical and Electronics Engineering; Başar, Ertuğrul; Faculty Member; Department of Electrical and Electronics Engineering; College of Engineering; 149116Publication 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 Closed-form representations of field components of fluorescent emitters in layered media(Optical Soc Amer, 2009) Doğan, Mehmet; Swan, Anna K.; Goldberg, Bennett B.; Ünlü, M. Selim; Department of Electrical and Electronics Engineering; Aksun, M. İrşadi; Faculty Member; Department of Electrical and Electronics Engineering; College of Engineering; 28358Dipole radiation in and near planar stratified dielectric media is studied theoretically within the context of fluorescence microscopy, as fluorescent emitters are generally modeled by electric dipoles. Although the main emphasis of this study is placed on the closed-form representations of the field components of fluorescent emitters in layered environments in near- and far-field regions, the underlying motive is to understand the limits of spectral self-interference fluorescence microscopy in studying the dipole orientation of fluorophores. Since accurate calculations of the field components of arbitrarily polarized electric dipoles in layered environments are computationally very time-consuming, a method for finding their closed-form representations is proposed using the closed-form potential Green's functions previously developed for microwave applications. The method is verified on typical geometries used in spectral self-interference microscopy experiments, where a dipole emitter is positioned over a slab of SiO2 on top of a Si substrate. In addition to facilitating efficient calculation of near and intermediate fields of fluorescent emitters, closed-form Green's functions for fields would also play a crucial role in developing efficient and rigorous computational analysis and design tools for optical passive devices such as optical antennas by significantly improving the computational cost of the numerical solution of the integral equation.Publication Metadata only A novel orthogonal frequency division multiplexing with index modulation waveform with carrier frequency offset resistance and low peak-to-average power ratio(Wiley, 2022) Kucukyavuz, Defne; Onat, Furuzan Atay; N/A; Department of Electrical and Electronics Engineering; Gürol, İlter Erol; Başar, Ertuğrul; PhD Student; Faculty Member; Department of Electrical and Electronics Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; 149116In this paper, we propose a novel orthogonal frequency division multiplexing (OFDM) scheme with high carrier frequency offset (CFO) resistance and low peak-to-average power ratio (PAPR). In this scheme, we consider a hybrid model with two subblock types, namely, pilot subblocks and standard subblocks. In pilot subblocks, active subcarriers are utilized for PAPR reduction while inactive carriers generated by the index modulation (IM) are utilized for the coarse CFO estimation. For standard subblocks, we consider unique subcarrier activation patterns (SAPs) with high-diversity IM to enhance the bit error performance of the overall system. Additionally, the inactive data tones in standard subblocks are utilized for fine CFO estimation, which enhances the CFO estimation quite significantly. Furthermore, in this paper, we show that proposed hybrid OFDM-IM (H-OFDM-IM) scheme can outperform conventional OFDM-IM and classical OFDM both in CFO estimation and PAPR reduction without requiring transmission of any side information. Finally, we show both mathematically and through computer simulations that proposed H-OFDM-IM can achieve a satisfactory bit error rate (BER) performance under high CFO scenarios.Publication Metadata only Stochastic modeling and optimization for energy management in multicore systems: a video decoding case study(IEEE-Inst Electrical Electronics Engineers Inc, 2008) Yaldız, Soner; Department of Electrical and Electronics Engineering; Department of Electrical and Electronics Engineering; Demir, Alper; Taşıran, Serdar; Faculty Member; Faculty Member; Department of Electrical and Electronics Engineering; College of Engineering; College of Engineering; 3756; N/AThis paper presents a novel stochastic modeling and optimization framework for energy minimization in multicore systems running real-time applications with tolerance to deadline misses. This framework is based on stochastic application models, which capture the variability of and the spatial and temporal correlations among the workloads of concurrent and interdependent tasks that constitute the application. These stochastic models are utilized in novel mathematical formulations to obtain optimal energy management policies. Experimental results on MPEG2 video decoding show that significant energy savings can be achieved, often close to the theoretical upper bound.