Browsing Institute of Materials Science and Nanotechnology (UNAM) by Issue Date
Now showing 1 - 20 of 2260
Results Per Page
Item Open AccessBenchmarking a microfluidic-based filtration for isolating biological particles(American Chemical Society, 8-02-20) İnci, Fatih; İnci, FatihIsolating particles from complex fluids is a crucial approach in multiple fields including biomedicine. In particular, biological matrices contain a myriad of distinct particles with different sizes and structures. Extracellular vesicles (EVs), for instance, are nanosized particles carrying vital information from donor to recipient cells, and they have garnered significant impact on disease diagnostics, drug delivery, and theranostics applications. Among all the EV types, exosome particles are one of the smallest entities, sizing from 30 to 100 nm. Separating such small substances from a complex media such as tissue culture and serum is still one of the most challenging steps in this field. Membrane filtration is one of the convenient approaches for these operations; yet clogging, low-recovery, and high fouling are still major obstacles. In this study, we design a two-filter-integrated microfluidic device focusing on dead-end and cross-flow processes at the same time, thereby minimizing any interfering factors on the recovery. The design of this platform is also numerically assessed to understand pressure-drop and flow rate effects over the procedure. As a model, we isolate exosome particles from human embryonic kidney cells cultured in different conditions, which also mimic complex fluids such as serum. Moreover, by altering the flow direction, we refresh the membranes for minimizing clogging issues and benchmark the platform performance for multitime use. By comprehensively analyzing the design and operation parameters of this platform, we address the aforementioned existing barriers in the recovery, clogging, and fouling factors, thereby achieving the use of a microfluidic device multiple times for bio-nanoparticle isolation without any notable issues. Item Open AccessOn-chip flow rate sensing via membrane deformation and bistability probed by microwave resonators(Springer Link, 8-04-2023) Seçme, Arda; Pisheh, Hadi Sedaghat; Tefek, Uzay; Uslu, H. Dilara; Küçükoğlu, Berk; Alataş, Ceren; Kelleci, Mehmet; Hanay, Mehmet Selim; Seçme, Arda; Pisheh, Hadi Sedaghat; Tefek, Uzay; Uslu, H. Dilara; Küçükoğlu, Berk; Alataş, Ceren; Kelleci, Mehmet; Hanay, Mehmet SelimPrecise monitoring of fluid flow rates constitutes an integral problem in various lab-on-a-chip applications. While off-chip flow sensors are commonly used, new sensing mechanisms are being investigated to address the needs of increasingly complex lab-on-a-chip platforms which require local and non-intrusive flow rate sensing. In this regard, the deformability of microfluidic components has recently attracted attention as an on-chip sensing mechanism. To develop an on-chip flow rate sensor, here we utilized the mechanical deformations of a 220 nm thick Silicon Nitride membrane integrated with the microfluidic channel. Applied pressure and fluid flow induce different modes of deformations on the membrane, which are electronically probed by an integrated microwave resonator. The flow changes the capacitance, and in turn resonance frequency, of the microwave resonator. By tracking the resonance frequency, liquid flow was probed with the device. In addition to responding to applied pressure by deflection, the membrane also exhibits periodic pulsation motion under fluid flow at a constant rate. The two separate mechanisms, deflection and pulsation, constitute sensing mechanisms for pressure and flow rate. Using the same device architecture, we also detected pressure-induced deformations by a gas to draw further insight into the sensing mechanism of the membrane. Flow rate measurements based on the deformation and instability of thin membranes demonstrate the transduction potential of microwave resonators for fluid–structure interactions at micro- and nanoscales. Item Open AccessInvestigation of thin films SiO2 obtained by low temperature plasmachemical deposition(American Institute of Physics, 1994-07-26) Timofeev, F. N.; Bozkurt, K.; Gure, M.; Aydınlı, Atilla; Süzer, Şefik; Ellialtioglu, R.; Turkoglu, K.; Süzer, Şefik; Aydınlı, Atilla Item Open AccessVisible photoluminescence from thin films of SiOx prepared by low-temperature plasmachemical deposition(American Institute of Physics, 1994-07-26) Timofeev, F. N.; Mikhailov, V. N.; Timofeev, I. N.; Aydınlı, Atilla; Süzer, Şefik; Ellialtioglu, R.; Gure, M.; Turkoglu, K.; Süzer, Şefik; Aydınlı, Atilla Item Open AccessLens geometries for quantitative acoustic microscopy(Springer, 1995) Atalar, Abdullah; Köymen, Hayrettin; Bozkurt, Ayhan; Yaralıoğlu, Göksenin; Atalar, Abdullah; Köymen, Hayrettin; Briggs, A.; Arnold, W.The purpose of the first Lemons-Quate acoustic microscope(1) was to image the surfaces of materials or biological cells with a high resolution. Unfortunately, competition with the optical microscope was only partially successful due to the high degree of absorption in the liquid-coupling medium at high frequencies. Increasing the resolution beyond optical limits was possible with the use of hot water(2) or cryogenic liquids,(3) at the cost of operational difficulty and system complexity. Meanwhile it was shown that the acoustic microscope can generate information that has no counterpart in the optical world.(4) The presence of leaky waves resulted in an interference mechanism known as V(z) curves. The V(z) method involves recording the reflected signal amplitude from an acoustic lens as a function of distance between the lens and the object. This recorded signal is shown to depend on elastic parameters of the object material. After underlying processes are well understood, new lens geometries or signal-processing electronics are designed to emphasize the advantage of the acoustic lens. In any case, the aim has been to increase the quantitative characterization ability of the microscope. Item Open AccessOptimized dipole antennas on photonic band gap crystals(American Institute of Physics, 1995) Cheng, S. D.; Biswas, R.; Özbay, Ekmel; McCalmont, S.; Tuttle, G.; Ho, K.-M.; Özbay, EkmelPhotonic band gap crystals have been used as a perfectly reflecting substrate for planar dipole antennas in the 12-15 GHz regime. The position, orientation, and driving frequency of the dipole antenna on the photonic band gap crystal surface, have been optimized for antenna performance and directionality. Virtually no radiated power is lost to the photonic crystal resulting in gains and radiation efficiencies larger than antennas on other conventional dielectric substrates.© 1995 American Institute of Physics. Item Open AccessLaser-micromachined millimeter-wave photonic band-gap cavity structures(American Institute of Physics, 1995) Özbay, Ekmel; Tuttle, G.; McCalmont, J. S.; Sigalas, M.; Biswas, R.; Soukoulis, C. M.; Ho, K. M.; Özbay, EkmelWe have used laser-micromachined alumina substrates to build a three-dimensional photonic band-gap crystal. The rod-based structure has a three-dimensional full photonic band gap between 90 and 100 GHz. The high resistivity of alumina results in a typical attenuation rate of 15 dB per unit cell within the band gap. By removing material, we have built defects which can be used as millimeter-wave cavity structures. The resulting quality ~Q! factors of the millimeter-wave cavity structures were as high as 1000 with a peak transmission of 10 dB below the incident signal. © 1995 American Institute of Physics. Item Open AccessDefect structures in a layer-by-layer photonic band-gap crystal(American Physical Society, 1995) Özbay, Ekmel; Tuttle, G.; Sigalas, M.; Soukoulis, C. M.; Ho, K. M.; Özbay, EkmelWe have experimentally and theoretically investigated defect structures that are incorporated into a three-dimensional layer-by-layer photonic band-gap crystal. The defects are formed by either adding or removing dielectric material to or from the crystal. For both cases, we observed localized modes with frequencies that lie within the forbidden band gap of the pure crystal. Relatively high peak transmission (10 dB below the incident signal), and high quality factors (2000) have been measured. These measurements were in good agreement with theoretical simulations. Theoretical calculations also predict very high (Q>106) quality factors for certain cavity structures. © 1995 The American Physical Society. Item Open AccessPole-zero computation in microwave circuits using multipoint Padé approximation(Institute of Electrical and Electronics Engineers, 1995-01) Celik, M.; Ocali, O.; Tan, M. A.; Atalar, AbdullahA new method is proposed for dominant pole- zero (or pole-residue) analysis of large linear microwave circuits containing both lumped and distributed elements. The method is based on a multipoint Padé approximation. It finds a reduced-order rational s-domain transfer function using a data set obtained by solving the circuit at only a few frequency points. We propose two techniques in order to obtain the coefficients of the transfer function from the data set. The proposed method provides a more efficient computation of both transient and frequency domain responses than conventional simulators and more accurate results than the techniques based on single-point Padé approximation such as asymptotic waveform evaluation. Item Open AccessTransient analysis of nonlinear circuits by combining asymptotic waveform evaluation with volterra series(Institute of Electrical and Electronics Engineers, 1995-08) Celik, M.; Atalar, Abdullah; Tan, M. A.A new method is proposed for the transient analysis of circuits with large number of linear lumped elements and lossy coupled transmission lines, and with few mildly nonlinear terminations. The method combines the Volterra-series technique with Asymptotic Waveform Evaluation approach and corresponds to recursive analysis of a linear equivalent circuit. Item Open AccessContact imaging in the atomic force microscope using a higher order flexural mode combined with a new sensor(A I P Publishing LLC, 1996-01) Minne, S. C.; Manalis, S. R.; Atalar, Abdullah; Quate, C. F.Using an atomic force microscope (AFM) with a silicon cantilever partially covered with a layer of zinc oxide (ZnO), we have imaged in the constant force mode by employing the ZnO as both a sensor and actuator. The cantilever deflection is determined by driving the ZnO at the second mechanical resonance while the tip is in contact with the sample. As the tip‐sample force varies, the mechanical boundary condition of the oscillating cantilever is altered, and the ZnO electrical admittance is changed. Constant force is obtained by offsetting the ZnO drive so that the admittance remains constant. We have also used the ZnO as an actuator and sensor for imaging in the intermittent contact mode. In both modes, images produced by using the ZnO as a sensor are compared to images acquired with a piezoresistive sensor. Item Open AccessA new method for nonlinear circuit simulation in time domain: NOWE(Institute of Electrical and Electronics Engineers, 1996-03) Ocalı, O.; Tan, M. A.; Atalar, AbdullahA new method for the time-domain solution of general nonlinear dynamic circuits is presented. In this method, the solutions of the state variables are computed by using their time derivatives up to some order at the initial time instant. The computation of the higher order derivatives is equivalent to solving the same linear circuit for various sets of dc excitations. Once the time derivatives of the state variables are obtained, an approximation to the solution can be found as a polynomial rational function of time. The time derivatives of the approximation at the initial time instant are matched to those of the exact solution. This method is promising in terms of execution speed, since it can achieve the same accuracy as the trapezoidal approximation with much smaller number of matrix inversions. Item Open AccessIndependent parallel lithography using the atomic force microscope(A I P Publishing LLC, 1996-05) Minne, S. C.; Manalis, S. R.; Atalar, Abdullah; Quate, C. F.Independent parallel features have been lithographically patterned with a 2×1 array of individually controlled cantilevers using an atomic force microscope. Control of the individual cantilevers was achieved with an integrated piezoelectric actuator in feedback with a piezoresistive sensor. Patterns were formed on 〈100〉 single crystal silicon by using a computer controlled tip voltage to locally enhance the oxidation of the silicon. Using the piezoresistor directly as a force sensor, parallel images can be simultaneously acquired in the constant force mode. A discussion of electrostatic forces due to applied tip voltages, hysteresis characteristics of the actuator, and the cantilever system is also presented. Item UnknownComputer aided frequency planning for the radio and TV broadcasts(Institute of Electrical and Electronics Engineers, 1996-06) Altıntaş, Ayhan; Ocalı, O.; Topçu, Satılmış; Tanyer, S. G.; Köymen, Hayrettin; Altıntaş, Ayhan; Ocalı, O.; Topçu, Satılmış; Köymen, HayrettinThe frequency planning of the VHF and UHF broadcasts in Turkey is described. This planning is done with the aid of computer databases and digital terrain map. The frequency offset is applied whenever applicable to increase the channel capacity. The offset assignment is done through simulated annealing algorithm. The international rules and regulations concerning Turkey are also considered. Item UnknownReflection properties and defect formation in photonic crystals(A I P Publishing LLC, 1996-08-05) Özbay, Ekmel; Temelkuran, B.; Özbay, EkmelWe have investigated the surface reflection properties of a layer-by-layer photonic crystal. By using a Fabry-Perot resonant cavity analogy along with the reflection-phase information of the photonic crystal, we predicted defect frequencies of planar defect structures. Our predictions were in good agreement with the measured defect frequencies. Our simple model can also predict and explain double defect formation within the photonic band gap. Item UnknownHigh‐speed atomic force microscopy using an integrated actuator and optical lever detection(A I P Publishing LLC, 1996-09) Manalis, S. R.; Minne, S. C.; Atalar, Abdullah; Quate, C. F.A new procedure for high‐speed imaging with the atomic force microscope that combines an integrated ZnO piezoelectric actuator with an optical lever sensor has yielded an imaging bandwidth of 33 kHz. This bandwidth is primarily limited by a mechanical resonance of 77 kHz when the cantilever is placed in contact with a surface. Images scanned with a tip velocity of 1 cm/s have been obtained in the constant force mode by using the optical lever to measure the cantilever stress. This is accomplished by subtracting an unwanted deflection produced by the actuator from the net deflection measured by the photodiode using a linear correction circuit. We have verified that the tip/sample force is constant by monitoring the cantilever stress with an implanted piezoresistor. Item UnknownLayer-by-layer photonic crystals from microwave to far-infrared frequencies(Optical Society of America, 1996-09) Özbay, Ekmel; Özbay, EkmelThe use of layer-by-layer geometry to build photonic band-gap crystals at various frequencies ranging from microwave to the far-infrared is described. The layer-by-layer structure yields a full photonic band gap in all directions, and this is experimentally confirmed at microwave frequencies. The structures are then built at smaller scales by means of silicon micromachining with photonic band-gap frequencies as high as 500 GHz. Transmission characteristics and the reflection characteristics of the millimeter-wave photonic crystals are reported The use of laser-micromachined alumina substrates to build three-dimensional millimeter-wave photonic crystals is also described. Defect structures are investigated at microwave and millimeter-wave frequencies. Item UnknownPhotonic band gaps with layer-by-layer double-etched structures(A I P Publishing LLC, 1996-09-03) Biswas, R.; Özbay, Ekmel; Ho, K. M.; Özbay, EkmelPeriodic layer‐by‐layer dielectric structures with full three‐dimensional photonic band gaps have been designed and fabricated. In contrast to previous layer‐by‐layer structures the rods in each successive layer are at an angle of 70.5° to each other, achieved by etching both sides of a silicon wafer. Photonic band‐structure calculations are utilized to optimize the photonic band gap by varying the structural geometry. The structure has been fabricated by double etching Si wafers producing millimeter wavephotonic band gaps between 300 and 500 GHz, in excellent agreement with band calculations. Overetching this structure produces a multiply connected geometry and increases both the size and frequency of the photonic band gap, in very good agreement with experimental measurements. This new robust double‐etched structure doubles the frequency possible from a single Si wafer, and can be scaled to produced band gaps at higher frequencies. © 1996 American Institute of Physics Item UnknownInterdigital cantilevers for atomic force microscopy(A I P Publishing LLC, 1996-10) Manalis, S. R.; Minne, S. C.; Atalar, Abdullah; Quate, C. F.We present a sensor for the atomic force microscope (AFM) where a silicon cantilever is micromachined into the shape of interdigitated fingers that form a diffraction grating. When detecting a force, alternating fingers are displaced while remaining fingers are held fixed. This creates a phase sensitive diffraction grating, allowing the cantilever displacement to be determined by measuring the intensity of diffracted modes. This cantilever can be used with a standard AFM without modification while achieving the sensitivity of the interferometer and maintaining the simplicity of the optical lever. Since optical interference occurs between alternating fingers that are fabricated on the cantilever, laser intensity rather than position can be measured by crudely positioning a photodiode. We estimate that the rms noise of this sensor in a 10 hz–1 kHz bandwidth is ∼0.02 Å and present images of graphite with atomic resolution. Item UnknownA new method for the steady-state analysis of periodically excited nonlinear circuits(Institute of Electrical and Electronics Engineers, 1996-12) Celik, M.; Atalar, Abdullah; Tan, M. A.We propose a new method for the steady state analysis of periodically excited nonlinear microwave circuits. It is a modified and more efficient form of Newton-Raphson iteration based harmonic balance (HB) technique. It solves the convergence problems of the HB technique at high drive levels. The proposed method makes use of the parametric dependence of the circuit responses on the excitation level. It first computes the derivatives of the complex amplitudes of the harmonics with respect to the excitation level efficiently and then finds the Pade approximants for the amplitudes of the harmonics using these derivatives.