Researcher:
Çakmak, Onur

Profile Picture
ORCID

Job Title

PhD Student

First Name

Onur

Last Name

Çakmak

Name

Name Variants

Çakmak, Onur

Email Address

Birth Date

Filters

2011 - 201512

Advanced Search

Filter by

Settings

Researcher Of Publications: search.filters.isAuthorOfPublication.2fb7598b-6a1c-405e-998f-9822180d491e

Search Results

Now showing 1 - 10 of 12
  • Placeholder
    PublicationMetadata only
    Resonant PZT MEMS scanners with integrated angle sensors
    (IEEE Computer Society, 2014) Brown, Dean; Davis, Wyatt; N/A; Department of Electrical and Electronics Engineering; N/A; Department of Electrical and Electronics Engineering; Baran, Utku; Holmstrom, Sven; Çakmak, Onur; Ürey, Hakan; Master Student; Researcher; PhD Student; Faculty Member; Department of Electrical and Electronics Engineering; Graduate School of Sciences and Engineering; College of Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; N/A; 8579
    Several high performing PZT-actuated MEMS laser scanners utilizing mechanical coupling are designed, fabricated, and characterized. Optical angles up to 59.3 deg. and θoptD·fn-products up to 3052 deg.·mm·Hz are demonstrated. These are the highest performing MEMS scanners in the literature. An angle sensor is integrated into one scanner design without any additional processing. The sensor response shows a linear relationship with the mirror rotation. A closed-loop drive was demonstrated using the scanner output.
  • Placeholder
    PublicationMetadata only
    Precision density and viscosity measurement using two cantilevers with different widths
    (2015) Kılınç, Necmettin; Yaralıoğlu, G. G.; N/A; Department of Mechanical Engineering; Department of Electrical and Electronics Engineering; Çakmak, Onur; Ermek, Erhan; Ürey, Hakan; PhD Student; Other; Faculty Member; Department of Mechanical Engineering; Department of Electrical and Electronics Engineering; Graduate School of Sciences and Engineering; College of Sciences; College of Engineering; N/A; N/A; 8579
    Weintroduceanovelmethodforfastmeasurementofliquidviscosityanddensityusingtwocantilevers withdifferentgeometries.Ourmethodcanbeusedforreal-timemonitoringinlabonchipsystemsand offerhighaccuracyforalargerangeofdensitiesandviscosities.Themeasurementprincipleisbasedon trackingtheoscillationfrequenciesoftwocantileverswithaphase-lockedloop(PLL)andcomparingwith referencemeasurementswithaknownfluid.Asetofequationsandasimplealgorithmisdevelopedto relatethedensityandtheviscositytothefrequencyshiftsofthecantilevers.Wefoundthattheeffectof thedensityandtheviscositycanbewellseparatedifcantilevershavedifferentwidths.Intheexperiments, twoNickelmicrocantilevers(widths25 mand100 m,length:200 m,thickness:1.75 m)werefully immersedintheliquidandthetemperaturewascontrolled.TheactuationwasusinganexternalelectrocoilandtheoscillationsweremonitoredusinglaserDopplervibrometer.Thus,electricalconnectionsto thecantileversarenotrequired,enablingmeasurementsalsoinconductiveliquids.ThePLLisusedto setthephasedifferenceto90◦betweentheactuatorandthesensor.Calibrationmeasurementswere performedusingglycerolandethyleneglycolsolutionswithknowndensitiesandviscosities.Themeasurementerrorwiththenewmethodwaslowerthan3%indensityintherange995–1150kg/m3and 4.6%inviscosityintherange0.935–4mPa.s.Basedonthesignal-to-noiseratio,theminimumdetectable differenceintheviscosityis1 Pa.sandthedensityis0.18kg/m3.Furtherimprovementsintherange andtheaccuracyarepossibleusing3ormorecantileverswithdifferentgeometries.
  • Placeholder
    PublicationMetadata only
    A dynamic model of an overhung rotor with ball bearings
    (Sage, 2011) Şanlıtürk, K. Y.; N/A; Çakmak, Onur; PhD Student; Graduate School of Sciences and Engineering; N/A
    A ball bearing comprising rolling elements, inner and outer rings, and a cage structure can be described as a multi-body system (MBS). In order to predict the dynamic behaviour and resonance characteristics of a rotor-ball bearing system, it can be modelled and analysed as a MBS with flexible and rigid parts. In this study, a ball bearing is modelled with MBS approach using MSC ADAMS commercial software. The Hertzian theory is used for modelling the contact dynamics between the balls and the rings. The ball bearing model is then assembled with the rotor model which comprised a shaft and a disc positioned at the free end of the shaft. The ball bearing model is used with both flexible and rigid shaft assumptions in order to highlight the differences between the two cases. For the flexible shaft case, the MBS model also included a finite element model of the shaft. As expected, it is necessary to include the flexibility of the shaft in the model in order to to predict the changes in the modal characteristics of the system as a function of the rotor speed. Furthermore, including the gyroscopic effects leads to observe the forward and backward travelling modes with different natural frequencies. The effects of the bearing diametral clearance and localized defects on the inner and outer rings are modelled and analysed using the model developed. Also, the effects of the rotor unbalance on the vibration level of the whole system are examined. A test rig - consisting of two ball bearings, a shaft, and a disc - is also designed and developed so as to validate the theoretical model using experimental data. Order tracking and modal analyses are carried out and Campbell diagrams are obtained. Finally, the theoretical and the experimental results are compared and a refined MBS model is obtained for further analyses.
  • Placeholder
    PublicationMetadata only
    MEMS based blood plasma viscosity sensor without electrical connections
    (IEEE Computer Society, 2013) Yaralıoğlu, Göksenin G.; N/A; Department of Mechanical Engineering; Department of Electrical and Electronics Engineering; Department of Electrical and Electronics Engineering; Çakmak, Onur; Ermek, Erhan; Ürey, Hakan; Kılınç, Necmettin; PhD Student; Other; Faculty Member; Researcher; Department of Mechanical Engineering; Department of Electrical and Electronics Engineering; Graduate School of Sciences and Engineering; College of Engineering; College of Engineering; College of Engineering; N/A; N/A; 8579; 59959
    A MEMS based viscometer is reported. The device has a disposable cartridge and a reader. The cartridge contains microfluidic channels and a MEMS cantilever sensor. The reader contains the actuator and the readout optics and electronics. A unique feature of the system is that both the actuation and the sensing are remote; therefore, no electrical connections are required between the reader and the cartridge. The reported sensor is capable of measuring viscosity with better than 0.01 cP resolution in a range of 0.8-14.1 cP, with less than 50 μl sample requirement. This range and sensitivity are sufficient for blood plasma viscosity measurements, which are in between 1.1-1.3 cP for healthy individuals and can be elevated to 3cP in certain diseases[1].
  • Placeholder
    PublicationMetadata only
    MEMS biosensor for blood plasma viscosity measurements
    (Elsevier Science Bv, 2012) N/A; Department of Electrical and Electronics Engineering; Department of Mechanical Engineering; N/A; N/A; Department of Molecular Biology and Genetics; Department of Chemical and Biological Engineering; Department of Mechanical Engineering; Department of Electrical and Electronics Engineering; Çakmak, Onur; Elbüken, Çağlar; Ermek, Erhan; Bulut, Selma; Kılınç, Yasin; Barış, İbrahim; Kavaklı, İbrahim Halil; Alaca, Burhanettin Erdem; Ürey, Hakan; PhD Student; Researcher; Other; PhD Student; PhD Student; Teaching Faculty; Faculty Member; Faculty Member; Faculty Member; Department of Molecular Biology and Genetics; Department of Chemical and Biological Engineering; Department of Mechanical Engineering; Department of Electrical and Electronics Engineering; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Graduate School of Sciences and Engineering; College of Engineering; College of Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; College of Engineering; College of Engineering; College of Engineering; N/A; N/A; N/A; N/A; N/A; 111629; 40319; 115108; 8579
    N/A
  • Placeholder
    PublicationMetadata only
    Two cantilever based sytem for viscosity and density monitoring
    (IEEE, 2015) Yaralıoğlu, Göksenin G.; N/A; N/A; N/A; Department of Electrical and Electronics Engineering; Çakmak, Onur; Ermek, Erhan; Kılınç, Necmettin; Ürey, Hakan; PhD Student; Other; Researcher; Faculty Member; Department of Electrical and Electronics Engineering; Graduate School of Sciences and Engineering; College of Sciences; N/A; College of Engineering; N/A; N/A; 59959; 8579
    Viscosity and density measurements in liquids in real-time is challenging. Previous MEMS based approaches use frequency sweeps for the purpose and those methods are slow and not real-time. We show that high precision viscosity and density measurements are possible using two cantilevers with different widths and by tracking their frequencies with a Phase-Locked-Loop in real-time.
  • Placeholder
    PublicationMetadata only
    Microcantilever based loc system for coagulation measurements
    (Chemical and Biological Microsystems Society, 2014) Kılınç, Necmettin; Yaralıoğlu G.G.; N/A; Department of Molecular Biology and Genetics; Department of Molecular Biology and Genetics; Department of Molecular Biology and Genetics; Department of Electrical and Electronics Engineering; Çakmak, Onur; Ermek, Erhan; Barış, İbrahim; Kavaklı, İbrahim Halil; Ürey, Hakan; PhD Student; Other; Teaching Faculty; Faculty Member; Faculty Member; Department of Molecular Biology and Genetics; Department of Electrical and Electronics Engineering; Graduate School of Sciences and Engineering; College of Sciences; College of Sciences; College of Sciences; College of Sciences; N/A; N/A; 111629; 40319; 8579
    In this paper, a microcantilever-based system enabling multiple coagulation tests on the same disposable cartridge is demonstrated. The system consists of independent cartridge and reader unit. The actuation of the nickel cantilevers is conducted remotely with an external electro-coil and remote optical read-out is utilized for sensing. Both Prothrombin Time (PT) and activated Partial Thromboplastin Time (aPTT) tests can be conducted on the same cartridge. The system's repeatability and accuracy is investigated with standard control plasma samples. The results are concordant with the manufacturer's datasheet. The architecture of the system and the repeatable results makes the system suitable for Point-of-Care applications.
  • Placeholder
    PublicationMetadata only
    LoC sensor array platform for real-time coagulation measurements
    (Institute of Electrical and Electronics Engineers (IEEE), 2014) Yaralıoğlu, Göksenin G.; N/A; Department of Electrical and Electronics Engineering; Department of Mechanical Engineering; Department of Electrical and Electronics Engineering; Department of Electrical and Electronics Engineering; Department of Electrical and Electronics Engineering; Çakmak, Onur; Kılınç, Necmettin; Ermek, Erhan; Mostafazadeh, Aref; Elbüken, Çağlar; Ürey, Hakan; PhD Student; Researcher; Other; Researcher; Researcher; Faculty Member; Department of Mechanical Engineering; Department of Electrical and Electronics Engineering; Graduate School of Sciences and Engineering; College of Engineering; College of Sciences; College of Engineering; College of Engineering; College of Engineering; N/A; 59959; N/A; N/A; N/A; 8579
    This paper reports a MEMS-based sensor array enabling multiple clot-time tests in one disposable microfluidic cartridge using plasma. The versatile LoC (Lab-on-Chip) platform technology is demonstrated here for real-time coagulation tests (activated Partial Thrompoblastin 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, which consists of multiple microfluidic channels and MEMS microcantilevers placed in each channel. Microcantilevers are made of electro-plated nickel and actuated remotely using an external electro-coil. The read-out is also conducted remotely by a laser and the phase of the MEMS oscillator is monitored real-time. The system is capable of monitoring coagulation time with a precision estimated at 0.1sec.
  • Placeholder
    PublicationMetadata only
    Fabrication of 1D ZNO nanostructures on mems cantilever for VOC sensor application
    (Elsevier, 2014) Kosemen, Arif; Öztürk, Sadullah; Yerli, Yusuf; Öztürk, Zafer Ziya; Department of Electrical and Electronics Engineering; N/A; Department of Mechanical Engineering; Department of Electrical and Electronics Engineering; Kılınç, Necmettin; Çakmak, Onur; Ermek, Erhan; Ürey, Hakan; Researcher; PhD Student; Other; Faculty Member; Department of Mechanical Engineering; Department of Electrical and Electronics Engineering; College of Engineering; Graduate School of Sciences and Engineering; College of Engineering; College of Engineering; 59959; N/A; N/A; 8579
    This study reports the fabrication method and sensing performance for novel 1D zinc oxide (ZnO) nanorods and nanotubes grown on nickel MEMS cantilevers. The fabrication of the nanostructures and the cantilevers are simple and low-cost using standard lithography, electrodeposition, and hydrothermal etching processes. 1D ZnO nanostructures increase the total sensitive area for biological and chemical sensor applications. We performed experiments with various VOCs with a real-time sensor system developed in our laboratory. While Ni microcantilevers produced no signal, ZnO nanostructure coated microcantilevers showed good sensitivity and repeatable changes. Furthermore, the nanotube coated microcantilevers showed more than 10 fold increase in sensitivity compared to the nanorod coated microcantilevers which can be explained to the fact that ZnO nanotubes have higher surface area and subsurface oxygen vacancies and these provide a larger effective surface area with higher surface-to-volume ratio as compared to ZnO nanorods. The tests are performed using dynamic mode of operation near resonant frequency using magnetic actuation and optical sensing. The phase stability and the limit of detection of ZnO nanotube coated microcantilevers exposed to diethylamine (DEA) were 0.02 degrees and lower than 10 ppm, respectively. ZnO nanostructure coated microcantilevers have good potential for VOC sensor applications especially for amine groups.
  • Placeholder
    PublicationMetadata only
    Microcantilever based disposable viscosity sensor for serum and blood plasma measurements
    (Academic Press Inc Elsevier Science, 2013) N/A; Department of Mechanical Engineering; Department of Mechanical Engineering; Department of Electrical and Electronics Engineering; Department of Molecular Biology and Genetics; Department of Mechanical Engineering; Department of Chemical and Biological Engineering; Çakmak, Onur; Elbüken, Çağlar; Ermek, Erhan; Mostafazadeh, Aref; Barış, İbrahim; Alaca, Burhanettin Erdem; Kavaklı, İbrahim Halil; Ürey, Hakan; PhD Student; Researcher; Faculty Member; Researcher; Teaching Faculty; Faculty Member; Faculty Member; Faculty Member; Department of Electrical and Electronics Engineering; Department of Molecular Biology and Genetics; Department of Mechanical Engineering; Department of Chemical and Biological Engineering; Graduate School of Sciences and Engineering; College of Engineering; College of Engineering; Graduate School of Sciences and Engineering; College of Sciences; College of Engineering; College of Engineering; N/A; N/A; N/A; N/A; 111629; 115108; 40319; 8579
    This paper proposes a novel method for measuring blood plasma and serum viscosity with a microcantilever-based MEMS sensor. MEMS cantilevers are made of electroplated nickel and actuated remotely with magnetic field using an electro-coil. Real-time monitoring of cantilever resonant frequency is performed remotely using diffraction gratings fabricated at the tip of the dynamic cantilevers. Only few nanometer cantilever deflection is sufficient due to interferometric sensitivity of the readout. The resonant frequency of the cantilever is tracked with a phase lock loop (PLL) control circuit. The viscosities of liquid samples are obtained through the measurement of the cantilever's frequency change with respect to a reference measurement taken within a liquid of known viscosity. We performed measurements with glycerol solutions at different temperatures and validated the repeatability of the system by comparing with a reference commercial viscometer. Experimental results are compared with the theoretical predictions based on Sader's theory and agreed reasonably well. Afterwards viscosities of different Fetal Bovine Serum and Bovine Serum Albumin mixtures are measured both at 23 degrees C and 37 degrees C, body temperature. Finally the viscosities of human blood plasma samples taken from healthy donors are measured. The proposed method is capable of measuring viscosities from 0.86 cP to 3.02 cP, which covers human blood plasma viscosity range, with a resolution better than 0.04 cP. The sample volume requirement is less than 150 mu l and can be reduced significantly with optimized cartridge design. Both the actuation and sensing are carried out remotely, which allows for disposable sensor cartridges. (C) 2013 Published by Elsevier Inc.