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YARALIOĞLU, Göksen Göksenin

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Göksen Göksenin

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YARALIOĞLU
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    Vertical cavity capacitive transducer
    (American Institute of Physics Inc., 2021-04-01) Yaralıoğlu, Göksen Göksenin; Ergun, A. S.; Bozkurt, A.; Electrical & Electronics Engineering; YARALIOĞLU, Göksen Göksenin
    The capacitive micromachined ultrasonic transducer (CMUT) has inherent advantages, such as larger bandwidth and monolithic integration capability with electronics, when compared to the piezoelectric transducer. The most significant shortcoming of the device is the trade-off between input and output sensitivities. Adequate receive sensitivity requires an electric field intensity on the order of 105 V/m, which can be achieved by sub-micron gap heights. However, a small gap limits the device stroke and, consequently, the maximum output pressure. This paper addresses this problem by proposing a CMUT with a vertical cavity. The membrane of the device has a piston part that is surrounded by the sidewalls of a vertical cylinder formed in the substrate. The fringing electric field pulls the piston in the vertical direction; hence, the gap height remains fixed, which alleviates the hard limit on device stroke. The performance of the proposed device is compared to that of the conventional CMUT by theoretical and analytical methods, and a micro-fabrication method is devised. Additionally, a millimeter-scale device has been manufactured and tested as a proof of concept.
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    Mutual radiation impedance of circular CMUTs on a cylinder
    (IEEE, 2016) Zangabad, R. P.; Bozkurt, A.; Yaralıoğlu, Göksen Göksenin; Bosch, J. G.; Soest, G. van; Steen, A. F. W. van der; Electrical & Electronics Engineering; YARALIOĞLU, Göksen Göksenin
    In ultrasound imaging, cross coupling of transducer elements through the medium has significant effect on the frequency response, thus affecting the quality of the ultrasound image. In Side-Looking Intravascular Ultrasound (SL-IVUS) imaging a radial image of the vessel wall is formed using a transducer array in a cylindrical configuration. Recent advances in Capacitive Micromachined Ultrasound Transducer (CMUT) fabrication and integration techniques led to realization of CMUT arrays that can be wrapped into a cylinder shape and mounted on a catheter tip. In this paper, we present the calculation of radiation impedance of un-collapse CMUT arrays on a planar rigid baffle and on a cylinder using Finite Element Method (FEM) simulation. We link the crosstalk between planar CMUT elements with dips in frequency spectrum from experimental data and conclude that decreasing the cylinder radius causes downshift of the dips in frequency response. In the case of our device, these changes are too small to have detrimental effects on the array bandwidth.
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    Design of a quad element patch antenna at 5.8 GHz
    (IEEE, 2018) Majidi, Negar; Yaralıoğlu, Göksen Göksenin; Sobhani, M. R.; Imeci, T.; Electrical & Electronics Engineering; YARALIOĞLU, Göksen Göksenin; Majidi, Negar
    This paper presents simulation and experimental verification of a quad microstrip patch antenna that operates at 5.8 GHz. Sonnet antenna design software was used to simulate the performance of the antenna. To reduce the design's complexity and the computational load, the antenna and the feeding lines were simulated separately. An optimization was done for each subpart to get the optimum desired results. Finally, all the subparts were merged and the final structure was simulated to check the performance. A prototype of the antenna was fabricated on a double sided PCB substrate (relative permittivity=10.2, thickness=1.28 mm) using a PCB milling machine. The s 11 of -14 dB and -18.8 dB and maximum gain of 6.2 dB and 4.2 dB were obtained, from the simulation and experimental measurements, respectively.
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    Blood clotting time measurement using a miniaturized high-frequency ultrasound sensor
    (IEEE, 2023) Sobhani, M. R.; Majidi, Negar; Yaralıoğlu, Göksen Göksenin; Electrical & Electronics Engineering; YARALIOĞLU, Göksen Göksenin; Majidi, Negar
    This paper demonstrates a novel blood coagulation time measurement methodology that requires as low as 1 microliter of whole blood. The blood sample is placed on the top surface of a fused quartz plate where an ultrasonic transducer is fabricated on the bottom surface. The location of the blood sample is aligned with the transducer; therefore, the reflected acoustic waves from the blood/quartz interface are captured and converted to electrical signals by the transducer. The transducer is made of an 8 μm thick zinc oxide (ZnO) thin film that operates at 400 MHz. The acoustic impedance of blood changes due to the coagulation process. This affects the reflection coefficient and amplitude of the reflected waves from the blood/quartz interface. Thus, the blood coagulation time is determined by monitoring the amplitude of reflected acoustic waves. In the experiments, whole blood was used without any sample preparation. The method was tested using citrated blood with calcium chloride and activated partial thromboplastin (aPTT) reagents. We observed that aPTT coagulation times lengthened from 25 sec. to 47 sec. with the addition of heparin. The proposed method has the potential to be used in a disposable low-cost portable coagulation time measurement cartridge for patient self-testing.
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    Equivalent circuit for capacitive micromachined ultrasonic transducers to predict anti-resonances
    (Springer Nature, 2020-12) Kemal, Remzi Erkan; Bozkurt, A.; Yaralıoğlu, Göksen Göksenin; Electrical & Electronics Engineering; YARALIOĞLU, Göksen Göksenin; Kemal, Remzi Erkan
    Equivalent circuit models have been long used to evaluate the dynamics of the capacitive micromachined ultrasonic transducer (CMUT). An important parameter in the characterization of a CMUT is the anti-resonance frequency, which limits the immersion bandwidth. However, there is no equivalent circuit model that can accurately determine the anti-resonance frequency of a membrane. In this work, we present an improved lumped element parametric model for immersed CMUT. We demonstrate that the proposed equivalent circuit model accurately predicts anti-resonance and higher order mode frequencies, in addition to that of the fundamental mode. The proposed circuit model is in good agreement with device characteristics calculated using the finite element method and experimentally measured data.
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    A pilot project for power quality improvements in distribution system by a Li-ion battery
    (IEEE, 2022) Çetin, A.; Ozen, C.; Bayatmakoo, A.; Kaya, K.; Poyrazoğlu, Göktürk; Electrical & Electronics Engineering; YARALIOĞLU, Göksen Göksenin
    Power quality (PQ) metrics deterioration occurs in the distribution system by increasing the distributed generation plants, the existence of non-linear and harmonic loads. As a distribution system operator running under the Turkishelectricity regulation, a battery investment was made to improve PQ metrics to provide quality electricity service to customers by focusing on Volt/VAr optimization to obtain voltage stability parameters. The reverse power flow caused by the distributed generation can be eliminated and the power factor would be improved with the reactive support with this investment. This study includes the reasons for the battery pilot project, the engineering methodology, and post-solution improvements.
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    Blood coagulation time measurement using a 1μL of whole blood on a TE mode BAW resonator
    (IEEE, 2018-12-20) Majidi, Negar; Sobhani, M. R.; Yaralıoğlu, Göksen Göksenin; Electrical & Electronics Engineering; YARALIOĞLU, Göksen Göksenin; Majidi, Negar
    This paper presents a possible way to blood coagulation time measurement using a TE (Thickness Extensions) mode BAW (Bulk Acoustic Wave) resonator which requires as low as 1 micro-liter of whole blood. The blood sample is placed on the top surface of a glass plate where a compressional ultrasonic transducer is fabricated on the bottom surface. The transducer is made of 8 μm thick zinc oxide (ZnO) thin film that has a thickness resonance frequency around 400 MHz. The transducer generates compressional (longitudinal) acoustic wave inside the piezoelectric thin film and glass substrate. The acoustic waves are mostly reflected and trapped inside the device from both sides of it; 1) the glass/liquid (blood) interface, and 2) the transducer/air interface. Most of the acoustic waves are reflected from the second interface because of the higher impedance mismatch, while the reflections from the first boundary are related to impedance (mechanical properties) of the liquid sample or blood. The acoustic impedance of blood changes due to the coagulation process. This affects the reflection coefficient and amplitude of the reflected waves from the blood/glass interface. Thus, the overall acoustic energy trapped inside the bulk film changes over the time which consequently affects the resonator parameters. The blood coagulation time was determined by monitoring the amplitude of the reflected sinusoidal acoustic waves at 400 MHz in the previous work using the same device. However, in this paper we demonstrate the resonance frequency shifts obtained by numerical modeling and practical measurements for a few liquid samples with different mechanical properties. The proposed method has a potential to be used in a low-cost portable coagulation time measurement cartridge which requires only 1μL of whole blood without centrifuging. A simple resonator can be implemented for tracking the resonating frequency to further reduce the size and cost of the device, to make it more suitable for patient self-testing applications.
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    Analysis of vibratory gyroscopes: drive and sense mode resonance shift by coriolis force
    (IEEE, 2017) Cetin, Hakan; Yaralıoğlu, Göksen Göksenin; Electrical & Electronics Engineering; YARALIOĞLU, Göksen Göksenin; Cetin, Hakan
    In this paper, we demonstrate the analysis of coupling between drive and sense systems of vibratory gyroscopes. Vibratory gyroscopes have attracted a lot of interest recently with the development of MEMS gyroscopes. These gyroscopes made their way through portable devices and smart phones. Novel gyroscope architectures have been proposed and analyzed in detail. However, in most of these analyses, coupling between the sense and drive systems was ignored. We analytically show that drive and sense systems are coupled together via Coriolis and centrifugal force. As a result, system resonances shift as the rotation rate increase for linear and torsional gyroscope systems. Starting from a simple gyro system, we calculated the sense and drive resonant frequency shifts in various configurations. Then, for more complex systems where analytical solution is difficult to obtain, we used commercially available FEM tools to determine corresponding frequency shift. In general, we found that the shift is small and can be ignored for linear vibratory gyroscopes where Q of the sense system is less than 2500 for mode matched gyros. But for higher Q systems, the frequency shift may affect the linearity of these gyroscopes. This sets a fundamental limit for the linearity of vibratory gyroscopes. Based on our calculations the non-linearity is above 1% for linear 2-DOF mode-matched vibratory gyroscopes where Q is above 3000 and for torsional 2-DOF vibratory gyroscopes where Q is above 600. Multi-DOF and ring vibratory gyroscopes are also examined. We find that the effect is less pronounced for Multi-DOF gyros, whereas there is a large effect on the linearity of ring gyroscopes.
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    Receive-noise analysis of capacitive micromachined ultrasonic transducers
    (IEEE, 2016) Bozkurt, A.; Yaralıoğlu, Göksen Göksenin; Electrical & Electronics Engineering; YARALIOĞLU, Göksen Göksenin
    This paper presents an analysis of thermal (Johnson) noise received from the radiation medium by otherwise noiseless capacitive micromachined ultrasonic transducer (CMUT) membranes operating in their fundamental resonance mode. Determination of thermal noise received by multiple numbers of transducers or a transducer array requires the assessment of cross-coupling through the radiation medium, as well as the self-radiation impedance of the individual transducer. We show that the total thermal noise received by the cells of a CMUT has insignificant correlation, and is independent of the radiation impedance, but is only determined by the mass of each membrane and the electromechanical transformer ratio. The proof is based on the analytical derivations for a simple transducer with two cells, and extended to transducers with numerous cells using circuit simulators. We used a first-order model, which incorporates the fundamental resonance of the CMUT. Noise power is calculated by integrating over the entire spectrum; hence, the presented figures are an upper bound for the noise. The presented analyses are valid for a transimpedance amplifier in the receive path. We use the analysis results to calculate the minimum detectable pressure of a CMUT. We also provide an analysis based on the experimental data to show that output noise power is limited by and comparable to the theoretical upper limit.
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    Cantilever array oscillators with nonlinear optical readout
    (IEEE, 2015) Lüleç, S. Z.; Adiyan, U.; Yaralıoğlu, Göksen Göksenin; Leblebici, Y.; Urey, H.; Electrical & Electronics Engineering; YARALIOĞLU, Göksen Göksenin
    MEMS array oscillators typically require a separate detector and feedback loop for each oscillator. We show that grating-based-optical-readout induces nonlinearity, which enables simultaneous operation of an array-of-oscillators using only one detector and single electronic feedback-loop.