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Permanent URI for this collectionhttps://hdl.handle.net/20.500.14288/6

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Department: search.filters.department.Department of Electrical and Electronics EngineeringSubject: search.filters.subject.Nanoscience and nanotechnology

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Now showing 1 - 10 of 21
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    PublicationOpen Access
    Plasmon-coupled photocapacitor neuromodulators
    (American Chemical Society (ACS), 2020) Ülgüt, Burak; Çetin, Arif E.; N/A; N/A; Department of Molecular Biology and Genetics; Department of Electrical and Electronics Engineering; Department of Chemical and Biological Engineering; Melikov, Rustamzhon; Srivastava, Shashi Bhushan; Karatüm, Onuralp; Doğru-Yüksel, Itır Bakış; Jalali, Houman Bahmani; Sadeghi, Sadra; Dikbaş, Uğur Meriç; Kavaklı, İbrahim Halil; Nizamoğlu, Sedat; PhD Student; Researcher; PhD Student; PhD Student; Master Student; Faculty Member; Faculty Member; Department of Molecular Biology and Genetics; Department of Electrical and Electronics Engineering; Department of Chemical and Biological Engineering; Graduate School of Sciences and Engineering; College of Sciences; College of Engineering; N/A; N/A; N/A; N/A; N/A; N/A; N/A; 40319; 130295
    Efficient transduction of optical energy to bioelectrical stimuli is an important goal for effective communication with biological systems. For that, plasmonics has a significant potential via boosting the light-matter interactions. However, plasmonics has been primarily used for heat-induced cell stimulation due to membrane capacitance change (i.e., optocapacitance). Instead, here, we demonstrate that plasmonic coupling to photocapacitor biointerfaces improves safe and efficacious neuromodulating displacement charges for an average of 185% in the entire visible spectrum while maintaining the faradic currents below 1%. Hot-electron injection dominantly leads the enhancement of displacement current in the blue spectral window, and the nanoantenna effect is mainly responsible for the improvement in the red spectral region. The plasmonic photocapacitor facilitates wireless modulation of single cells at three orders of magnitude below the maximum retinal intensity levels, corresponding to one of the most sensitive optoelectronic neural interfaces. This study introduces a new way of using plasmonics for safe and effective photostimulation of neurons and paves the way toward ultrasensitive plasmon-assisted neurostimulation devices.
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    PublicationOpen Access
    Nonlinear nanomechanical mass spectrometry at the single-nanoparticle level
    (American Chemical Society (ACS), 2019) Yüksel, Mert; Orhan, Ezgi; Yanık, Cenk; Arı, Atakan B.; Hanay, M. Selim; Department of Electrical and Electronics Engineering; Demir, Alper; Faculty Member; Department of Electrical and Electronics Engineering; College of Engineering; 3756
    Nanoelectromechanical systems (NEMS) have emerged as a promising technology for performing the mass spectrometry of large biomolecules and nanoparticles. As nanoscale objects land on NEMS sensors one by one, they induce resolvable shifts in the resonance frequency of the sensor proportional to their weight. The operational regime of NEMS sensors is often limited by the onset of nonlinearity, beyond which the highly sensitive schemes based on frequency tracking by phase-locked loops cannot be readily used. Here, we develop a measurement architecture with which to operate at the nonlinear regime and measure frequency shifts induced by analytes in a rapid and sensitive manner. We used this architecture to individually characterize the mass of gold nanoparticles and verified the results by performing independent measurements of the same nanoparticles based on linear mass sensing. Once the feasibility of the technique is established, we have obtained the mass spectrum of a 20 nm gold nanoparticle sample by individually recording about 500 single-particle events using two modes working sequentially in the nonlinear regime. The technique obtained here can be used for thin nanomechanical structures that possess a limited dynamic range.
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    PublicationOpen Access
    Silicon microsphere photonics - art. no. 65931J
    (Society of Photo-optical Instrumentation Engineers (SPIE), 2007) Department of Physics; Department of Electrical and Electronics Engineering; Serpengüzel, Ali; Kurt, Adnan; Ayaz, Ulaş Kemal; Faculty Member; Teaching Faculty; Department of Physics; Department of Electrical and Electronics Engineering; College of Sciences; 27855; 194455; N/A
    Electrophotonic integrated circuits (EPICs), or alternatively, optoelectronic integrated circuit (OEICs) are the natural evolution of the microelectronic integrated circuit (IC) with the added benefit of photonic capabilities. Traditionally, the microelectronics IC industry has been based on group IV silicon, whereas the microphotonics industry on group III-V semiconductors. However, silicon based photonic microdevices have been making strands in "siliconizing" photonics. Silicon microspheres with their high quality factor whispering gallery modes (WGMs), are ideal candidates for wavelength division multiplexing (WDM) in the standard near-infrared telecommunications bands. In our experiments, we are using silicon microspheres with a refractive index of 3.48 and a radius of 500 micrometers. The optical resonances of the silicon microspheres provide the necessary narrow linewidths, that are needed for high resolution WDM applications. Potential WDM applications include filters, modulators, switches, detectors, and possibly light sources.
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    PublicationOpen Access
    Minimum energy channel codes for nanoscale wireless communications
    (Institute of Electrical and Electronics Engineers (IEEE), 2013) Department of Electrical and Electronics Engineering; Kocaoğlu, Murat; Akan, Özgür Barış; PhD Student; Department of Electrical and Electronics Engineering; College of Engineering
    It is essential to develop energy-efficient communication techniques for nanoscale wireless communications. In this paper, a new modulation and a novel minimum energy coding scheme (MEC) are proposed to achieve energy efficiency in wireless nanosensor networks (WNSNs). Unlike existing studies, MEC maintains the desired code distance to provide reliability, while minimizing energy. It is analytically shown that, with MEC, codewords can be decoded perfectly for large code distances, if the source set cardinality is less than the inverse of the symbol error probability. Performance evaluations show that MEC outperforms popular codes such as Hamming, Reed-Solomon and Golay in the average codeword energy sense.
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    PublicationOpen Access
    An information theoretical analysis of multi-terminal neuro-spike communication network in spinal cord
    (Association for Computing Machinery (ACM), 2018) Department of Electrical and Electronics Engineering; Akan, Özgür Barış; Civaş, Meltem; Faculty Member; Department of Electrical and Electronics Engineering; College of Engineering; Graduate School of Sciences and Engineering; 6647; N/A
    Communication theoretical understanding of healthy and diseased connections in the spinal cord motor system is crucial for realizing future information and communication technology (ICT) based diagnosis and treatment techniques for spinal cord injuries (SCI). A spinal cord motor nucleus associated with a particular muscle constitutes an ideal candidate for studying to have an understanding of SCI. Typical spinal cord motor nucleus system contains pool of lower motor neurons (MNs) controlling a muscle by integrating synaptic inputs from spinal interneurons (INs), upper motor neurons (DNs) and sensory neurons (SNs). In this study, we consider this system from ICT perspective. Our aim is to quantify the rate of information flow across a spinal cord motor nucleus. To this end, we model an equivalent single-hop multiterminal network, where multiple transmitting nodes representing heterogeneous population of DNs, INs and SNs sen information to multiple receiving nodes corresponding to MNs. To identify the outputs at receiving nodes, we define corresponding neurospike communication channel and then find the bound on total rates across this network. Based on the network model, we analyze achievable rates for a particular motor nucleus system called Tibialis Anterior (TA) motor nucleus in the spinal cord numerically and simulate several spinal cord dysfunction scenarios. The numerical results reveal that decrease in the maximum total rates with the lower motor neuron injury causes weakness in the affected muscle.
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    PublicationOpen Access
    FR4-based electromagnetic energy harvester for wireless tyre sensor nodes
    (Elsevier, 2009) Department of Electrical and Electronics Engineering; Hatipoğlu, Gökhan; Ürey, Hakan; Faculty Member; Department of Electrical and Electronics Engineering; College of Engineering; N/A; 8579
    An electromagnetic (EM) power generator having 46 Hz resonance frequency is designed to scavenge mechanical vibrations occurring in tyres due to lyre-road contact. The major innovation is the use of FR4 as a structural spring material as well as utilizing a spacer and stopper mechanism increasing the shock resistance by limiting the maximum deflection. The novel magnet assembly and spacer design provide high power density. The tangential acceleration waveforms of typical tyre rotation is used as an input in the experiments and 0.4 mW power is obtained over a 100 Omega load resistance for 15g peak-to-peak amplitude at 22,83 Hz, corresponding to about 150 kph vehicle speed. Maximum acceleration is limited with the shaker, larger power values are expected in actual operation. The performance is obtained off-resonance and superior to resonant Silicon MEMS based scavengers.
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    PublicationOpen Access
    Large spectral tuning of liquid microdroplets by local heating with a focused infrared laser
    (Society of Photo-optical Instrumentation Engineers (SPIE), 2008) Department of Physics; Department of Electrical and Electronics Engineering; Kiraz, Alper; Karadağ, Yasin; Yorulmaz, Saime Çiğdem; Muradoğlu, Metin; Faculty Member; PhD Student; Faculty Member; Department of Physics; Department of Electrical and Electronics Engineering; College of Sciences; 22542; N/A; N/A; 46561
    Large deformations can easily be introduced in liquid microdroplets by applying relatively small external forces or controlling the evaporation/condensation kinetics. This makes liquid microdroplets attractive to serve as the building blocks of largely tunable optical switches or filters that are essential in optical communication systems based on wavelength division multiplexing. Solid optical microcavities have not found large use in these applications, mainly due to their rigid nature. The fact that liquid microdroplets are low-cost and disposable can also prove to be important in mass production of these photonic devices. Here, we show that local heating with an infrared laser can be used to largely tune the whispering gallery modes (WGMs) of water/glycerol or salty water microdroplets standing on a superhydrophobic surface. In the scheme presented, a liquid microdroplet kept in a humidity chamber is stabilized on a superhydrophobic surface, and an infrared laser beam is focused near tire center of the microdroplet. As a, result of the local treating, the temperature of the liquid microdroplet increases, and the water content in the liquid microdroplet evaporates until a new equilibrium is reached. At the new equilibrium state, the non-volatile component, (i.e. glycerol or salt) attains a higher concentration in the liquid microdroplet. We report tunability over large spectral ranges up to 30 run at around 590 nm. For salty water microdroplets the reported spectral timing mechanism is almost fully reversible, while for tire case of glycerol/water microdroplets the spectral timing mechanism can be made highly reversible when the chamber is saturated with glycerol vapor and the relative water humidity approaches unity.
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    PublicationOpen Access
    Hexagonal boron nitride incorporation to achieve high performance Li4Ti5O12 electrodes
    (American Institute of Physics (AIP) Publishing, 2020) Department of Electrical and Electronics Engineering; Ergen, Onur; Department of Electrical and Electronics 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; 272106
    There is an increasing demand for fast charging and high capacity lithium ion batteries. However, conventional Li-ion battery chemistries cannot meet the stringent requirements of these demands due to the poor performance of graphite anodes, especially on safety during fast charging. Finding the right anode material that can replace conventional graphite while providing high capacity is very challenging. Today, lithium titanium oxide (LTO) is considered one of the most attractive anode materials that can provide the desired ultra-fast charging ability (>10C) with high safety. However, it has many serious drawbacks when compared to the existing graphite anodes, including poor intrinsic conductivity, narrow electrochemical window, etc. Extensive research has been done to overcome these problems, especially in developing new LTO composite materials with reduced graphene oxide. However, even these methods have rapid capacity fading at high current densities, >5C, due to increased internal resistance and polarization losses. Here, we demonstrate an effective way to improve LTO composite materials by developing unique nanoengineered three-dimensional frameworks with hexagonal boron nitride (h-BN) addition. Li-ion cells with h-BN incorporation exhibit excellent performance and operational stability, especially at fast and ultra-fast charging rates, >10C.
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    PublicationOpen Access
    Statistical characterization and analysis of low-THz communication channel for 5G Internet of Things
    (Elsevier, 2019) Department of Electrical and Electronics Engineering; Akan, Özgür Barış; Abbasi, Naveed Ahmed; Khalid, Nabil; Faculty Member; Department of Electrical and Electronics Engineering; College of Engineering; Graduate School of Sciences and Engineering; 6647; N/A; N/A
    This paper presents measurements and statistical characterization to compare three potential bands of the low-THz channel, namely, the 300 to 319 GHz, 340 to 359 GHz and 380 to 399 GHz bands. From the large set of measurements performed in line-of-sight (LoS) and non-LoS (NLoS) environments, parameters for path loss model with shadowing are evaluated. Our results show that the path loss exponents for the band around 310 GHz, 350 GHz, and 390 GHz is 2.07, 1.90 and 1.96, respectively. The impacts of different materials acting as surfaces in LoS channels and reflectors in NLoS environments are also examined. Additionally, the statistical analysis due to temporal, spatial and multipath propagation is performed to determine the best fit distributions. Finally, we look at some networking scenarios in THz Band communication to derive the expressions for the number of connections a user can make based on antenna characteristics, data rate requirements and antenna mobility as well as network density. Our results suggest fundamental parameters that can be used in future THz Band analysis with applications in both macro and micro scale Internet of Things (IoT).
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    PublicationOpen Access
    Bio-inspired networking: from theory to practice
    (Institute of Electrical and Electronics Engineers (IEEE), 2010) Dressler, Falko; Department of Electrical and Electronics Engineering; Akan, Özgür Barış; Faculty Member; Department of Electrical and Electronics Engineering; College of Engineering
    Bio-inspired networking techniques have been investigated since more than a decade. Findings in this field have fostered new developments in networking, especially in the most challenging domains such as handling large-scale networks, their dynamic nature, resource constraints, heterogeneity, unattended operation, and robustness. Even though this new research area started with highly theoretical concepts, it can be seen that there is also practical impact. This article aims to give an overview to the general field of bio-inspired networking, introducing the key concepts and methodologies. Selected examples that outline the capabilities and the practical relevance are discussed in more detail. The presented examples outline the activities of a new community working on bio-inspired networking solutions, which is converging and becomes visible in term of the provided astonishingly efficient solutions.