Search for: dielectric-devices
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    Continuous size-based focusing and bifurcating microparticle streams using a negative dielectrophoretic system

    , Article Microfluidics and Nanofluidics ; Volume 14, Issue 1-2 , 2013 , Pages 265-276 ; 16134982 (ISSN) Hemmatifar, A ; Saidi, M. S ; Sadeghi, A ; Sani, M
    Dielectrophoresis (DEP) is an electrokinetic phenomenon which is used for manipulating micro- and nanoparticles in micron-sized devices with high sensitivity. In recent years, electrode-based DEP by patterning narrow oblique electrodes in microchannels has been used for particle manipulation. In this theoretic study, a microchannel with triangular electrodes is presented and a detailed comparison with oblique electrodes is made. For each shape, the behavior of particles is compared for three different configurations of applied voltages. Electric field, resultant DEP force, and particle trajectories for configurations are computed by means of Rayan native code. The separation efficiency of... 

    Dielectrophoretic cell sorting via sliding cells on 3D silicon microelectrodes

    , Article Proceedings of the IEEE International Conference on Micro Electro Mechanical Systems (MEMS), 22 January 2017 through 26 January 2017 ; 2017 , Pages 147-150 ; 10846999 (ISSN) ; 9781509050789 (ISBN) Xing, X ; Chan, M. L ; Roshan, K. A ; Yobas, L ; Sharif University of Technology
    This work presents an innovative design for a flow-through dielectrophoretic cell sorting based on silicon bulk microelectrodes featuring sidewall undercuts. The microelectrodes are configured into an interdigitated array with digits extending across the flow chamber at an oblique angle against the flow stream. Target cells under dielectrophoretic forces and hydrodynamic drag can slide along the digits to a dedicated outlet. The design has been showcased for continuous-flow sorting of viable and non-viable mammalian cells, achieving a throughput of 16,600 cells/min, an order of magnitude higher than those reported for existing continuous-flow cell sorting designs using thin-film or... 

    Proper measurement of pure dielectrophoresis force acting on a RBC using optical tweezers

    , Article Biomedical Optics Express ; Volume 10, Issue 11 , 2019 , Pages 5639-5649 ; 21567085 (ISSN) Sasanpour, M ; Azadbakht, A ; Mollaei, P ; S. Reihani, N. S ; Sharif University of Technology
    OSA - The Optical Society  2019
    The force experienced by a neutral dielectric object in the presence of a spatially non-uniform electric field is referred to as dielectrophoresis (DEP). The proper quantification of DEP force in the single-cell level could be of great importance for the design of high-efficiency micro-fluidic systems for the separation of biological cells. In this report we show how optical tweezers can be properly utilized for proper quantification of DEP force experienced by a human RBC. By tuning the temporal frequency of the applied electric field and also performing control experiments and comparing our experimental results with that of theoretically calculated, we show that the measured force is a... 

    Low-noise differential transimpedance amplifier structure based on capacitor cross-coupled gm-boosting scheme

    , Article Microelectronics Journal ; Volume 39, Issue 12 , 2008 , Pages 1843-1851 ; 00262692 (ISSN) Jalali, M ; Nabavi, A ; Moravvej Farshi, M. K ; Fotowat Ahmady, A ; Sharif University of Technology
    This paper presents a capacitor cross-coupled gm-boosting scheme for differential implementation of common-gate transimpedance amplifier (CG-TIA). A differential transimpedance amplifiers (DTIA) is designed by this scheme using two modified floating-biased CG stage with improved low corner frequency. Despite conventional methods for single-ended to differential conversion that increase the power and the noise for the same gain, the new DTIA gives a higher gain and hence reduces the input-referred noise power. Design of the DTIA circuit using 0.13 μm CMOS technology illustrates near 1.7 dB improvement in the circuit sensitivity and 5.2 dB enhancement in transimpedance gain compared to its... 

    Measurement of moisture and temperature profiles in different layers of soil

    , Article 3rd International Foundation Congress and Equipment Expo 2018: Case Histories and Lessons Learned, IFCEE 2018, 5 March 2018 through 10 March 2018 ; Volume 2018-March, Issue GSP 298 , 2018 , Pages 266-278 ; 08950563 (ISSN) Fazel Mojtahedi, F ; Ali, K ; Nazari, A ; Rezvani, S ; Khatami, A ; Ahmadi, N ; Deep Foundations Institute; International Association of Foundation Drilling; Pile Driving Contractors Association; The Geo-Institute (G-I) of the American Society of Civil Engineers (ASCE) ; Sharif University of Technology
    American Society of Civil Engineers (ASCE)  2018
    Over past decades, extensive research has been performed on the measurement of land subsidence as a result of compaction of aquifer. This paper describes results from a new field-monitoring system to evaluate changes in matric suction and temperature profiles in soil layers over an extended time period. The monitoring system used in this study consists of inserting dielectric sensors into a 105 m borehole, drilled in a site in Ardabil Plain, The monitoring results from the site were used to calibrate predictions from HYDRUS-1D. The physical and hydraulic properties of the soil materials in different layers were obtained through performing some soil characteristics and filter paper tests... 

    Proposing a high-efficiency dielectrophoretic system for separation of dead and live cells

    , Article Scientia Iranica ; Volume 25, Issue 1 , 2018 , Pages 186-195 ; 10263098 (ISSN) Shayestehpour, H ; Nassiri Nazif, K ; Soufi, A. M ; Saidi, M. S ; Sharif University of Technology
    Sharif University of Technology  2018
    Recently, electrode-based Dielectrophoresis (eDEP) has been used for particle manipulation by means of triangular electrodes. In this theoretical and numerical study, a microchannel with quarter-of-ellipse electrodes is presented and a detailed comparison with triangular electrodes is provided. Electric field, resultant DEP force, and particle trajectories for each microchannel are evaluated by means of COMSOL Multiphysics 4.4. Afterwards, focusing and separation efficiencies of the systems are assessed and compared. Finally, separation efficiency of our proposed model for live and dead cells is compared with that of our previous model published in the literature [1]. It is demonstrated that... 

    Dielectrophoretic interaction of two particles in a uniform electric field

    , Article Microsystem Technologies ; Volume 25, Issue 7 , 2019 , Pages 2699-2711 ; 09467076 (ISSN) Javidi, R ; Moghimi Zand, M ; Dastani, K ; Sharif University of Technology
    Springer Verlag  2019
    The local electric field distorsion induced by a dielectric particle leads to particle–particle interactions and assembly which is very interesting for their useful applications on microfluidic devices. Particles behavior becomes more complicated if several particles interact at the same time. This paper presents a comprehensive numerical analysis of the assembly and particle–particle interactions for two similar and dissimilar dielectric particles immersed in a dielectric fluid using the immersed interface method based on two-dimensional direct-current dielectrophoresis. The immersed interface method is a finite-difference (or finite element) based numerical method which its key advantage... 

    Simple, Cost-effective, and continuous 3D dielectrophoretic microchip for concentration and separation of bioparticles

    , Article Industrial and Engineering Chemistry Research ; Volume 59, Issue 9 , 2020 , Pages 3772-3783 Tajik, P ; Saidi, M. S ; Kashaninejad, N ; Nguyen, N. T ; Sharif University of Technology
    American Chemical Society  2020
    Dielectrophoresis is a robust approach for manipulating bioparticles in microfluidic devices. In recent years, many groups have developed dielectrophoresis-based microfluidic systems for separation and concentration of various types of bioparticles, where the gradient of the electric field causes dielectrophoresis force acting on the suspended particles. Enhancing the gradient of the electric field with three-dimensional (3D) electrodes can significantly improve the efficiency of the system. Implementing planar electrodes in a 3D arrangement is a simple option to form a 3D-electrode configuration. This paper reports the development of a novel dielectrophoretic microfluidic system for... 

    A dual-band circularly polarized antenna using a metallized ferrite disk

    , Article Journal of Magnetism and Magnetic Materials ; Volume 539 , 2021 ; 03048853 (ISSN) Bagheri, A ; Tavakol, M. R ; Rejaei, B ; Khavasi, A ; Sharif University of Technology
    Elsevier B.V  2021
    We have designed and fabricated a dual-band circularly polarized antenna using a normally magnetized ferrite disk. The disk is metallized on top and is mounted on a grounded dielectric substrate. A hole is then punched at the center of the top metallization. The dual band operation of the antenna is due to two separate unidirectional resonances. The field intensity at the lower resonance is largest close to the outer periphery of the disk whereas at the higher resonance the electromagnetic field is concentrates near the punched hole. A two-section feeding network is used to feed the antenna. Central frequencies of the upper and lower bands are 4.62 GHz and 5.97 GHz, respectively.... 

    Aerodynamic enhancement and improving the performance of a six-megawatt dowec wind turbine by micro-plasma actuator

    , Article International Journal of Mechanical Sciences ; Volume 195 , 2021 ; 00207403 (ISSN) Omidi, J ; Mazaheri, K ; Sharif University of Technology
    Elsevier Ltd  2021
    We have investigated the usage of a Dielectric Barrier Discharge (DBD) plasma actuator to improve the aerodynamic performance of an offshore 6 MW wind turbine. By controlling the aerodynamic load combined with pitch angles of 2, 5, and 10 degrees, we studied the plasma actuator effect on the overall harvested power. Actuators were installed in single and tandem configurations in different chord-wise locations to find the optimum design. The improved phenomenological model developed by authors was used in an analysis to simulate the interaction of the electrostatic field, the ionized particles and the fluid flow. A design software was used to estimate the harvested power of the real 3D blade.... 

    Phase noise characterization of oscillators through Ito calculus

    , Article International Journal of Circuit Theory and Applications ; Volume 43, Issue 11 , November , 2015 , Pages 1581-1596 ; 00989886 (ISSN) Jahanbakht, S ; Farzaneh, F ; Sharif University of Technology
    John Wiley and Sons Ltd  2015
    Recent phase noise analysis techniques of oscillators mainly rely on solving a stochastic differential equation governing the phase noise process. This equation has been solved in the literature using a number of mathematical tools from probability theory like deriving the Fokker-Planck equation governing the phase noise probability density function. Here, a completely different approach for solving this equation in presence of white noise sources is introduced that is based on the Ito calculus for stochastic differential equations. Time-domain analytical expressions for the correlation of the noisy variables of the oscillator are derived that in asymptotically large times give the... 

    Analysis of terahertz-induced optical phase modulation in a nonlinear dielectric slab

    , Article Progress In Electromagnetics Research M ; Volume 13 , 2010 , Pages 41-51 ; 19378726 (ISSN) Ghattan, Z ; Izadi, S. A ; Shahabadi, M ; Sharif University of Technology
    Frequency shift of the spectrum of an incident optical pulse by an intense THz pulse inducing cross-phase modulation (XPM) in a nonlinear dielectric slab is analyzed. The effect is predicted with a high degree of accuracy using the well-known transmission line matrix (TLM) technique. In this research, to model the THz-induced temporal and spatial variation of the dielectric permittivity of the nonlinear dielectric slab, the transmission lines of the TLM method are loaded with open shunt stubs. The parameters of the stubs are modified in accordance with the refractive index variation of the dielectric slab, here ZnTe, induced by the strong THz pulse. The obtained numerical results are... 

    Simulation of DBD plasma actuator effect on aerodynamic performance improvement using a modified phenomenological model

    , Article Computers and Fluids ; Volume 140 , 2016 , Pages 371-384 ; 00457930 (ISSN) Mazaheri, K ; Omidi, J ; Chaharlang Kiani, K ; Sharif University of Technology
    Elsevier Ltd  2016
    An improved phenomenological model is presented for numerical simulation of a Dielectric Barrier Discharge (DBD) plasma actuator for separation control of high angle of attack flow over a wind turbine airfoil. Based on existing numerical models and experimental measurements, a new model is proposed for prediction of the length of a plasma extent which is more consistent with previous observations. The electrical and hydrodynamic solvers used in the present study are validated against published experimental data. Then the applicability of a DBD actuator, mounted on a DU 91-W2-250 airfoil is extensively analyzed for a wide range of operating voltages and frequencies. The analysis is completely... 

    Improving the performance of a numerical model to simulate the EHD interaction effect induced by dielectric barrier discharge

    , Article International Journal of Heat and Fluid Flow ; Volume 67 , 2017 , Pages 79-94 ; 0142727X (ISSN) Omidi, J ; Mazaheri, K ; Sharif University of Technology
    Over the past decade, there has been a growing interest in dielectric-barrier-discharge (DBD) plasma actuators. The lack of a general model to accurately simulate the related phenomena is one of the primary limitations in studying such type of actuators. One of the most frequently used models of this type was proposed by Suzen and Huang (S-H). Despite the numerous efforts made to improve this model, including a recent work of the authors, some deficiencies still exist. In this study, new modifications have been introduced to improve the performance and accuracy of the S-H phenomenological model. Here, a relation between the electrical-potential and charge-density equations has been made in... 

    Power improvement of NREL 5-MW wind turbine using multi-DBD plasma actuators

    , Article Energy Conversion and Management ; Volume 146 , 2017 , Pages 96-106 ; 01968904 (ISSN) Ebrahimi, A ; Movahhedi, M ; Sharif University of Technology
    Elsevier Ltd  2017
    The present study numerically investigates the feasibility of using multiple dielectric barrier discharge (multi-DBD) plasma actuators as a novel approach for active flow control over a large horizontal axis wind turbine rotor. The National Renewable Energy Laboratory 5 MW offshore wind turbine is used as the baseline case. This turbine uses pitch control system to adjust the generated power above its rated wind speeds, but at lower speeds, this system remains inactive. In this paper, the operational condition speed is considered lower than the rated wind speed. The mathematical electro-static model is implemented to simulate the effects of plasma actuator on the external flow and the... 

    Experimental study of stall control over an airfoil with dual excitation of separated shear layers

    , Article Aerospace Science and Technology ; Volume 82-83 , 2018 , Pages 402-411 ; 12709638 (ISSN) Ebrahimi, A ; Hajipour, M ; Ghamkhar, K ; Sharif University of Technology
    This paper investigates the stall control over an airfoil employing dual excitation of separated shear layers with dielectric barrier discharge plasma actuators. This novel approach is studied experimentally on the NACA 0015 airfoil at the angle of attack and Reynolds number of 14° and 0.3×106, respectively. To analyze the baseline flow, Time-averaged pressure distributions on the airfoil surfaces are evaluated with 40 pressure taps. Further, the dominant natural frequencies associated with flow structures in the airfoil wake are examined utilizing a hot-wire anemometer. Two plasma actuators, one on the suction side just upstream the separation point and the other on the pressure side at the... 

    A low-power technique for high-resolution dynamic comparators

    , Article International Journal of Circuit Theory and Applications ; Volume 46, Issue 10 , 2018 , Pages 1777-1795 ; 00989886 (ISSN) Khorami, A ; Sharifkhani, M ; Sharif University of Technology
    John Wiley and Sons Ltd  2018
    A low-power technique for high-resolution comparators is introduced. In this technique, p-type metal-oxide-semiconductor field-effect transistors are employed as the input of the latch of the comparator just like the input of the preamplifier. The latch and preamplifier stages are activated in a special pattern using an inverter-based controller. Unlike the conventional comparator, the preamplification delay can be set to an optimum low value even if after the preamplification, the output voltages is less than n-channel metal-oxide semiconductor voltage threshold. As a result, the proposed comparator reduces the power consumption significantly and enhances the speed. The speed and power... 

    Numerical assessment of MILD combustion enhancement through plasma actuator

    , Article Energy ; Volume 183 , 2019 , Pages 172-184 ; 03605442 (ISSN) Mardani, A ; Khanehzar, A ; Sharif University of Technology
    Elsevier Ltd  2019
    One promising solution to achieve moderate or intense low-oxygen dilution (MILD) combustion under lower temperatures may be using non-equilibrium plasma discharge. Plasma assisted combustion can extend the flammability limits by reducing the auto-ignition temperature of the reactants and can be a great approach to achieve steady MILD combustion under extreme conditions through decreasing ignition delay time. In particular, the influence of the outlet flows from a co-flowing cylindrical dielectric barrier discharge (DBD) on the CH4/N2 combustion under MILD combustion has been investigated numerically through some simplifications on plasma discharge. A three streams coaxial burner are modeled... 

    Design of terahertz photoconductive antenna arrays based on defective photonic crystal substrates

    , Article Optics and Laser Technology ; Volume 114 , 2019 , Pages 89-94 ; 00303992 (ISSN) Rahmati, E ; Ahmadi Boroujeni, M ; Sharif University of Technology
    Elsevier Ltd  2019
    In this paper, arrays of two different terahertz (THz) antennas based on defective photonic crystal (DPC) substrates are proposed and their radiation characteristics are investigated by using full-wave simulation. We show that employing DPC substrates in THz photoconductive antenna (PCA) arrays reduces the amount of power coupled to the substrate surface waves and, as a result, decreases the mutual coupling between the elements of the antenna array and increases the directivity in the boresight direction. By studying 1 × 2 arrays of bowtie and four-leaf-clover-shaped antennas, we show that either the improvement of directivity in a broad bandwidth or the enhancement of photomixer antenna... 

    Microstructural, optical, and electrical characteristics of Ni/C doped BST thin films

    , Article Ceramics International ; Volume 45, Issue 5 , 2019 , Pages 5503-5510 ; 02728842 (ISSN) Emadi, F ; Nemati, A ; Hinterstein, M ; Adabifiroozjaei, E ; Sharif University of Technology
    Elsevier Ltd  2019
    In the present work the effect of simultaneous doping of carbon and nickel on the microstructural, optical, and electrical properties of barium strontium titanate (BST) is investigated. Thin films of BST were prepared by the sol-gel method in six different compositions ((Ba0.6Sr0.4)(NixCyTi1-x-y)O3): x = y = 0.00 (BST), x = 0.04 y = 0.00 (BST4N), x = 0.04 y = 0.01 (BST4N-1C), x = 0.04 y = 0.02 (BST4N-2C), x = 0.04 y = 0.03 (BST4N-3C), and x = y = 0.04 (BST4N-4C). Structural features and chemical bonds of the films were studied by TGA/DSC, XRD, FT-IR, and FE-SEM. The electrical and optical properties of the films were analysed by impedance spectroscopy and UV–VIS spectroscopy. The results...