Browsing by Author "Kulah, Haluk"

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Citation Count: Yıldırım, Ender; Özgür, E.; Külah, H.; "A Droplet Based Multi-Drug Screening System Controlled With Electrostatic Microvalves", Proceedings of the 16th International Conference On Miniaturized Systems for Chemistry and Life Sciences, Microtas 2012, pp. 959-961, (2012).
A Droplet Based Multi-Drug Screening System Controlled With Electrostatic Microvalves
(Chemical and Biological Microsystems Society, 2012) Yıldırım, Ender; Özgür, E.; Kulah, Haluk; 31835
This paper presents a droplet-based drug effect analysis system utilizing electrostatically-actuated normallyclosed microvalves to screen the effect of multiple drugs on a single type of cell. Proposed system minimizes the need for off-chip equipment by utilizing parylene based electrostatic microvalves. Prototypes of the system were fabricated and tested using colored DI water and 3 μm diameter micro beads, emulating drugs and cells respectively. During the tests, micro beads could be successfully entrapped in 137 pl droplets. Tests carried out with yeast cells also yielded successful encapsulation of the cells. It was shown that, switching between the drugs could be achieved by applying 200 V dc to operate the microvalves.
Citation Count: Eıldırım, E., Arıkan, M.A.S., Külah, H. (2012). A normally closed electrostatic parylene microvalve for micro total analysis systems. Sensors And Actuators A-Physical, 181, 81-86. http://dx.doi.org/10.1016/j.sna.2012.05.008
A normally closed electrostatic parylene microvalve for micro total analysis systems
(Elsevier Science SA, 2012) Yıldırım, Ender; Arıkan, M. A. Sahir; Kulah, Haluk; 120121
This paper presents an electrostatically actuated, normally closed microvalve for parylene microfluidics. The proposed valve structure isolates the fluid from the electric field, and hence results in relatively low actuation potentials (<60 V) irrespective of the working fluid. Hereby, the microvalve solves electrolysis or electrode shielding problems observed in electrostatic actuation in micro total analysis systems. To investigate leakage properties, microvalves were tested under pressurized flow with de-ionized (DI) water. No detectable leakage ratio was observed up to 20 kPa inlet pressure, due to the unique semicircular valve seat design. It was shown that the valve seat could be reconfigured to enable sealing at various pressure levels for different applications.
A Reconfigurable Microfluidic Transmitarray Unit Cell
(IEEE, 2013) Erdil, Emre; Topallı, Kağan; Zorlu, Özge; Toral, Taylan; Yıldırım, Ender; Kulah, Haluk; Aydın Çivi, Özlem; 31835)
This paper presents a novel microfluidics based approach to develop a reconfigurable circularly polarized transmitarray unit cell. The unit cell comprises double layer nested split ring slots formed as microfluidic channels that can be filled by fluids. Split regions in the slots are realized by injecting liquid metal into the channels. Beam steering is obtained by implementing rotational phase shifting via manipulating the liquid metal in the slots. X-band unit cell prototypes are fabricated on glass substrate carrying a patterned metal film, and the slot channels are formed by Polydimethylsiloxane (PDMS) using soft lithography techniques.
Citation Count: Turkyilmaz, S...et al. (2011). "An Electromagnetic Micro-Power Generator for Low Frequency Vibrations with Tunable Resonance", Eurosensors XXV, Vol. 25.
An Electromagnetic Micro-Power Generator for Low Frequency Vibrations With Tunable Resonance
(Elsevier Science BV, 2011) Türkyılmaz, S.; Zorlu, O.; Muhtaroğlu, A.; Kulah, Haluk
This paper presents an electromagnetic (EM) micro-power generator with tunable resonance frequency which can harvest energy from low frequency environmental vibrations. The reported power generator up-converts low frequency environmental vibrations before mechanical-to-electrical energy conversion by utilizing two diaphragms with different resonance frequencies. Power is generated through electromagnetic induction by a magnet attached to the low frequency diaphragm, and a 50 turn, 2.1 Omega coil, and a magnetic piece on the high frequency diaphragm. Both of the diaphragms are fixed to a common frame via rubber springs, which makes the resonance frequency of each diaphragm tunable. The fabricated prototype generates 5.2 mV and 3.21 mu W RMS power by up-converting 13 Hz, 7.5 mm peak-to-peak vibrations to 200 Hz. Tunability of the resonance frequency is experimentally verified by operating the same device at 2-30 Hz external vibrations. (C) 2011 Published by Elsevier Ltd.
Citation Count: Yildirim, E.; Kulah, H.; Arikan, M.A.S.,"An Electrostatically Actuated Parylene Microvalve for Lab-On-A-Chip Applications", 2011 16th International Solid-State Sensors, Actuators and Microsystems Conference, Transducers'11, pp. 250-253, (2011).
An Electrostatically Actuated Parylene Microvalve for Lab-On-A-Chip Applications
(2011) Yıldırım, Ender; Arıkan, M. A. Sahir; Kulah, Haluk; 31835
This paper presents a novel electrostatic microvalve to control in-plane flow on parylene based lab-on-a-chip-devices. Normally-closed design of the microvalve insulates the working fluid from the electric field, while providing low leakage up to 40 kPa inlet pressure. Prototypes are fabricated and tested for pull-in and flow characterization. Pull-in voltage is measured to be 150 V independent of the working fluid. No leakage is detected up to 20 kPa inlet pressure.
Citation Count: Yıldırım, E., Külah, H. (2011). Analysis and characterization of an electrostatically actuated in-plane parylene microvalve. Journal of Micromechanics and Microengineering, 21(10). http://dx.doi.org/10.1088/0960-1317/21/10/105009
Analysis and characterization of an electrostatically actuated in-plane parylene microvalve
(IOP Publishing LTD, 2011) Yıldırım, Ender; Kulah, Haluk; 31835; 120121
This paper presents analysis and implementation of a simple electrostatic microvalve designed for use in parylene-based lab-on-a-chip devices. The microvalve utilizes an in-plane collapsing diaphragm. To investigate the pull-in behavior of the diaphragm and flow characteristics, a thorough analysis is carried out using the finite element method. Microvalves with different diaphragm radii are fabricated using surface micromachining techniques. Pull-in tests are carried out under the no-flow condition with air, oil and water as the working fluid. Test results show that the pull-in occurs around 20 V for 450 mu m radius diaphragms with oil and air. However, it is not possible to observe pull-in up to 100 V (both ac and dc) for the case of water as the working fluid, due to its relatively high dielectric constant and conductivity. The flow tests show that no leakage flow was observed up to 4 kPa inlet pressure under 85 V actuation potential. The leakage ratio becomes 17% at 10 kPa inlet pressure. It is observed that the leakage can be reduced controllably by increasing the actuation potential, enabling the precise control of the flow rate
Citation Count: Yıldırım, E., Külah, H. (2012). Electrostatic energy harvesting by droplet-based multi-phase microfluidics. Microfluidics And Nanofluidics, 13(1), 107-111. http://dx.doi.org/10.1007/s10404-012-0946-2
Electrostatic energy harvesting by droplet-based multi-phase microfluidics
(Springer Heidelberg, 2012) Yıldırım, Ender; Kulah, Haluk; 120121
This paper presents an energy scavenging technique, merging microfluidics with electrostatic energy harvesting. The method employs droplet-based microflow of two phases with different electrical permittivities, resulting in a capacitance change across the microchannel, to harvest electrical energy. The technique is implemented on 3 mm wide, 1 mm deep minichannels. It is shown that 0.4 nW can be harvested using a single electrode pair, with air and water as the two phases flowing at 1 ml/min. The generated power can be increased significantly by microscale implementation, where the number of electrodes can also be increased for further improvement