ORCID Profile
0000-0001-5349-6319
Current Organisation
NASA Jet Propulsion Laboratory
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Publisher: American Chemical Society (ACS)
Date: 17-08-2016
Abstract: Ultrasensitive flexible strain sensors were developed through the combination of shear alignment of a high concentration graphene oxide (GO) dispersion with fast and precise patterning of multiple rectangular features on a flexible substrate. Resistive changes in the reduced GO films were investigated under various uniaxial strain cycles ranging from 0.025 to 2%, controlled with a motorized nanopositioning stage. The devices uniquely combine a very small detection limit (0.025%) and a high gauge factor with a rapid fabrication process conducive to batch production.
Publisher: Cold Spring Harbor Laboratory
Date: 16-04-2023
DOI: 10.1101/2023.04.13.536752
Abstract: The biomechanics of peripheral nerves are determined by the blood-nerve barrier (BNB), together with the epineural barrier, extracellular matrix, and axonal composition, which maintain structural and functional stability. These elements are often ignored in the fabrication of penetrating devices, and the implant process is traumatic due to the mechanical distress, compromising the function of neuroprosthesis for sensory-motor restoration in utees. Miniaturization of penetrating interfaces offers the unique opportunity of decoding in idual nerve fibers associated to specific functions, however, a main issue for their implant is the lack of high-precision standardization of insertion forces. Current automatized electromechanical force sensors are available however, their sensitivity and range litude are limited (i.e. mN), and have been tested only in-vitro . We previously developed a high-precision bi-directional micro-electromechanical force sensor, with a closed-loop mechanism (MEMS-CLFS), that while measuring with high-precision (−211.7μN to 211.5μN with a resolution of 4.74nN), can be used in alive animal. Our technology has an on-chip electrothermal displacement sensor with a shuttle beam displacement lification mechanism, for large range and high-frequency resolution (dynamic range of 92.9 dB), which eliminates the adverse effect of flexural nonlinearity measurements, observed with other systems, and reduces the mechanical impact on delicate biological tissue. In this work, we use the MEMS-CLFS for in-vivo bidirectional measurement of biomechanics in somatic and autonomic nerves. Furthermore we define the mechanical implications of irrigation and collagen VI in the BNB, which is different for both autonomic and somatic nerves (∼ 8.5-8.6 fold density of collagen VI and vasculature CD31+ in the VN vs ScN). This study allowed us to create a mathematical approach to predict insertion forces. Our data highlights the necessity of nerve-customization forces to prevent injury when implanting interfaces, and describes a high precision MEMS technology and mathematical model for their measurements.
Publisher: IEEE
Date: 11-2014
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 04-2020
Publisher: Springer Science and Business Media LLC
Date: 12-01-2012
Publisher: Wiley
Date: 02-11-2015
Abstract: Ultralight graphene-based cellular elastomers are found to exhibit nearly frequency-independent piezoresistive behaviors. Surpassing the mechanoreceptors in the human skin, these graphene elastomers can provide an instantaneous and high-fidelity electrical response to dynamic pressures ranging from quasi-static up to 2000 Hz, and are capable of detecting ultralow pressures as small as 0.082 Pa.
Publisher: ASMEDC
Date: 2011
Abstract: Increasing, demand for more efficient power generation forces turbomachinery to operate at higher temperatures and compression ratios. High speeds combined with high temperatures make turbomachinery sealing applications even more challenging. In order to confirm sufficient service life, seal material pairs should be tested similar to engine operating conditions. The high temperature friction and wear characteristics of cobalt superalloys, Haynes 25, 188 and 214 sheets, rubbed against Hastelloy X pins are presented in this work. Tests are conducted at 25, 200 and 400°C with a validated custom design linear reciprocating tribometer. Sliding speed and distance are 1Hz and 1.2 Km respectively. Friction coefficients are calculated with friction force data acquired from load cell and the dead weight where wear coefficient is calculated through mass loss after the tests.
Publisher: ASMEDC
Date: 2011
Abstract: A bump-type foil bearing consists of a compliant corrugated sheet metal supporting structure that is covered by a thin top foil surface. Bumps serve as stiffener and d ing elements to increase the stability of the system while top foil creates necessary wedge surface for aerodynamic film formation. Foil bearings are hard to analyze as flexible foil surface deforms and changes shape while aerodynamic film pressure forms. Fully coupled finite element approach is presented. To increase the accuracy, the geometry is discretized with quadratic hexagonal elements. The gas film is modeled by compressible Reynolds equation. The effect of velocity on load capacity will be investigated to reveal the performance of the code.
Publisher: IEEE
Date: 11-2014
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 12-2017
Publisher: Elsevier BV
Date: 12-2018
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 09-2018
Publisher: Royal Society of Chemistry (RSC)
Date: 2015
DOI: 10.1039/C5LC00836K
Abstract: A vibrating membrane with discontinuities in the form of through holes is utilised to achieve millisecond mixing.
Publisher: AIP Publishing
Date: 02-06-2014
DOI: 10.1063/1.4881263
Abstract: This work presents a microfabricated fringe-field capacitive pH sensor using interdigitated electrodes and an integrated modulation-based readout circuit. The changes in capacitance of the sensor result from the permittivity changes due to pH variations and are converted to frequency shifts using a crossed-coupled voltage controlled oscillator readout circuit. The shift in resonant frequency of the readout circuit is 30.96 MHz for a change in pH of 1.0–5.0. The sensor can be used for the measurement of low pH levels, such as gastric acid, and can be integrated with electronic pills. The measurement results show high repeatability, low noise, and a stable output.
Publisher: American Chemical Society (ACS)
Date: 27-03-2017
Abstract: Ultralight graphene elastomer-based flexible sensors are developed to detect subtle vibrations within a broad frequency range. The same device can be employed as an accelerometer, tested within the experimental bandwidth of 20-300 Hz as well as a microphone, monitoring sound pressures from 300 to 20 000 Hz. The sensing element does not contain any metal parts, making them undetectable by external sources and can provide an acceleration sensitivity of 2.6 mV/g, which is higher than or comparable to those of rigid Si-based piezoresistive microelectromechanical systems (MEMS).
Publisher: AIP Publishing
Date: 30-09-2013
DOI: 10.1063/1.4823828
Abstract: Microfabricated spiral inductors were employed for nanoscale displacement detection, suitable for use in implantable pressure sensor applications. We developed a variable inductor sensor consisting of two coaxially positioned planar coils connected in series to a measurement circuit. The devices were characterized by varying the air gap between the coils hence changing the inductance, while a Colpitts oscillator readout was used to obtain corresponding frequencies. Our approach shows significant advantages over existing methodologies combining a displacement resolution of 17 nm and low hysteresis (0.15%) in a 1 × 1 mm2 device. We show that resolution could be further improved by shrinking the device's lateral dimensions.
Publisher: AIP Publishing
Date: 14-04-2014
DOI: 10.1063/1.4871380
Publisher: IEEE
Date: 2020
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 10-2020
Publisher: ASMEDC
Date: 2010
Abstract: With the race for higher power and efficiency new gas turbines operate at ever increasing pressures and temperatures. Increased compression ratios and firing temperatures require many engine parts to survive extended service hours under large pressure loads and thermal distortions while sustaining relative vibratory motion. On the other hand, wear at elevated temperatures limits part life. Combined with rapid oxidation for most materials wear resistance reduces rapidly with increasing temperature. In order to achieve improved wear performance at elevated temperatures better understanding of combined wear and oxidation behavior of high temperature super alloys and coatings needed. In an attempt to aid designers for high temperature applications, this work provides a quick reference for the high temperature friction and wear research available in open literature. High temperature friction and wear data have been collected, grouped and summarized in tables.
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 08-2015
Publisher: AIP Publishing
Date: 07-2019
DOI: 10.1063/1.5109900
Abstract: Limited Z-axis bandwidth of piezotube scanners employed in conventional Scanning Tunneling Microscopes (STMs) has been a major limiting factor in achieving high scan speeds in STM applications. Slow Z-axis dynamics of typical piezotube scanners combined with the weight of the STM tip/tip holder assembly, that the scanner has to carry, substantially limit the achievable Z-axis bandwidth in both imaging and lithography modes. To tackle this issue, we propose a high bandwidth microelectromechanical-system-based nanopositioner to be integrated into an existing STM scanner. The device is designed to replace the STM tip and fine Z-positioning mechanisms in the conventional STM setup, while providing an order of magnitude higher bandwidth in Z axis. The device is microfabricated using double silicon-on-isolator technology, and standard cleanroom processes. Experiments show that tunneling current between the device tip and a highly ordered pyrolytic graphite s le can be successfully established and maintained in air using the proposed device in a feedback loop. Results indicate that the proposed device uniquely combines a very high resolution and a large stroke with a substantially larger Z-axis bandwidth compared to that of conventional STM piezotube scanners, enabling higher scanning speeds in STM operations.
Publisher: IEEE
Date: 08-2017
No related grants have been discovered for M. Bulut Coskun.