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dielectric
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Study of microstructure and dielectric properties of PMN-PZT ceramics via a mixed powder method including sol-gel precursor
, Article Journal of Alloys and Compounds ; Volume 476, Issue 1-2 , 2009 , Pages 791-796 ; 09258388 (ISSN) ; Nemati, Z. A ; Sharif University of Technology
2009
Abstract
An attempt to synthesize pyrochlore free (x)PMN-(1 - x)PZT ceramics (where x is 0, 0.1, 0.3, 0.5, 0.7, 0.9, and 1) by a mixed powder method was made. In this work, a sol-gel prepared PZT powder was mixed with the mixture of milled PbO, MgO and Nb2O5, and sintered in a two step sintering process. The produced samples with high PZT content showed low densities due to the low compaction ratio of PZT powder. The dielectric properties of PZT-rich and PMN-rich materials were high (with dielectric constant of about 19,000 and 33,000 for PZT-rich and PMN-rich ceramics, respectively) while the other samples exhibited low dielectric properties. Also, the effect of combining PMN with PZT on Curie...
Numerical assessment of MILD combustion enhancement through plasma actuator
, Article Energy ; Volume 183 , 2019 , Pages 172-184 ; 03605442 (ISSN) ; Khanehzar, A ; Sharif University of Technology
Elsevier Ltd
2019
Abstract
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...
Surface plasmon resonance of two-segmented Au-Cu nanorods
, Article Nanotechnology ; Volume 19, Issue 41 , 2008 ; 09574484 (ISSN) ; Iraji Zad, A ; Dolati, A ; Ghorbani, M ; Sharif University of Technology
2008
Abstract
Two-segmented gold-copper nanorods were electrodeposited inside the pores of polycarbonate track-etched membranes from two separate solutions. The PCT membranes were dissolved in dichloromethane (CH2Cl2) and the solvent was replaced by methanol solution. Optical absorption spectra of two-segmented Au-Cu nanorods dispersed in methanol showed two peaks which were related to the transverse mode of copper and the longitudinal mode of gold. By increasing the length of the gold segment, when the total length of both metals was fixed at 1 μm, the copper and gold peaks shifted to the blue and red wavelengths, respectively. We observed that the wavelengths of the extinction peaks are not in good...
Analysis of waveguide filters with dielectric resonators using multimode contour integral method
, Article Asia-Pacific Microwave Conference, APMC 2007, Bangkok, 11 December 2007 through 14 December 2007 ; 2007 ; 1424407494 (ISBN); 9781424407491 (ISBN) ; Banail, A ; Sharif University of Technology
2007
Abstract
The contour integral (CI) method is developed to analyze H-plane waveguide circuits filled with inhomogeneous dielectric such as circuits including full height dielectric posts. In order to reduce the computational costs, the multimode CI method, which considers the effect of higher order TEnO modes, is introduced and we present a hybrid method based on multimode CI and mode matching (MM) techniques. The accuracy of method is validated by comparison of results with those reported in literatures
Experimental investigation of the effect of active flow control on the wake of a wind turbine blade
, Article Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science ; Volume 235, Issue 22 , 2021 , Pages 6122-6138 ; 09544062 (ISSN) ; Davari, A. R ; Soltani, M. R ; Sharif University of Technology
SAGE Publications Ltd
2021
Abstract
An extensive experimental investigation was conducted to study the effects of Dielectric Barrier Discharge (DBD), on the flow field of an airfoil at low Reynolds number. The DBD was mounted near the leading edge of a section of a wind turbine blade. It is believed that DBD can postpone the separation point on the airfoil by injecting momentum to the flow. The effects of steady actuations on the velocity profiles in the wake region have been investigated. The tests were performed at α = 4 to 36 degrees i.e. from low to deep stall angles of attack regions. Both surface pressure distribution and wake profile show remarkable improvement at high angles of attack, beyond the static stall angle of...
Impact of dielectric barrier discharge plasma on the wake of a wind turbine blade section oscillating in plunge
, Article Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy ; 2021 ; 09576509 (ISSN) ; Davari, A. R ; Soltani, M. R ; Sharif University of Technology
SAGE Publications Ltd
2021
Abstract
Effects of dielectric barrier discharge plasma have been studied on the wake velocity profiles of a section of a 660 kW wind turbine blade in plunging motion in a wind tunnel. The corresponding unsteady velocity profiles show remarkable improvement when the plasma actuators were operating and the angles of attack of the model were beyond the static stall angles of the airfoil. As a result the drag force was considerably reduced. It is further observed that the plasma-induced flow attenuates the leading edge vortices that are periodically shed into wake and diminishes the large eddies downstream. The favorable effects of the plasma augmentation are shown to occur near the uppermost and...
Numerical analysis of a dielectrophoresis field-flow fractionation device for the separation of multiple cell types
, Article Journal of Separation Science ; Volume 40, Issue 20 , 2017 , Pages 4067-4075 ; 16159306 (ISSN) ; Kamali, A ; Sharif University of Technology
Abstract
In this study, a dielectrophoresis field-flow fractionation device was analyzed using a numerical simulation method and the behaviors of a set of different cells were investigated. By reducing the alternating current frequency of the electrodes from the value used in the original setup configuration and increasing the number of exit channels, total discrimination in cell trajectories and subsequent separation of four cell types were achieved. Cells were differentiated based on their size and dielectric response that are represented in their real part of Clausius–Mossotti factor at different frequencies. A number of novel designs were also proposed based on the original setup configuration....
Improvement of performance of polyamide reverse osmosis membranes using dielectric barrier discharge plasma treatment as a novel surface modification method
, Article Polymer Engineering and Science ; Volume 59 , 2019 , Pages E468-E475 ; 00323888 (ISSN) ; Asadollahi, M ; Mousavi, S. A ; Farhadi, F ; Sharif University of Technology
John Wiley and Sons Inc
2019
Abstract
In this research, surface modification of aromatic polyamide thin film composite (TFC) reverse osmosis (RO) membranes was carried out using dielectric barrier discharge (DBD) plasma treatment to improve the performance and fouling resistance of prepared RO membranes. First, polyamide TFC RO membranes were synthesized via interfacial polymerization of m-phenylenediamine and trimesoyl chloride monomers over microporous polysulfone support membrane. Next, the DBD plasma treatment with 15 s, 30 s, 60 s, and 90 s duration was used for surface modification. The surface properties of RO membranes were characterized by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR),...
Improvement of performance of polyamide reverse osmosis membranes using dielectric barrier discharge plasma treatment as a novel surface modification method
, Article Polymer Engineering and Science ; Volume 59 , 2019 , Pages E468-E475 ; 00323888 (ISSN) ; Asadollahi, M ; Mousavi, S. A ; Farhadi, F ; Sharif University of Technology
John Wiley and Sons Inc
2019
Abstract
In this research, surface modification of aromatic polyamide thin film composite (TFC) reverse osmosis (RO) membranes was carried out using dielectric barrier discharge (DBD) plasma treatment to improve the performance and fouling resistance of prepared RO membranes. First, polyamide TFC RO membranes were synthesized via interfacial polymerization of m-phenylenediamine and trimesoyl chloride monomers over microporous polysulfone support membrane. Next, the DBD plasma treatment with 15 s, 30 s, 60 s, and 90 s duration was used for surface modification. The surface properties of RO membranes were characterized by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR),...
Tailoring of structural, dielectric, and magnetic properties of SrBaCu2Fe12O22 hexaferrites by doping with Gd–Co binary mixtures
, Article Applied Physics A: Materials Science and Processing ; Volume 128, Issue 9 , 2022 ; 09478396 (ISSN) ; Khan, M. A ; Akhtar, M. N ; Gulbadan, S ; Ejaz, S. R ; Sharif University of Technology
Springer Science and Business Media Deutschland GmbH
2022
Abstract
Gadolinium (Gd) and cobalt (Co) substituted Sr–Ba–Cu-based Y-type hexaferrites were synthesized with the help of the sol–gel auto-combustion route. XRD (X-ray diffraction) analysis was done to ratify the phase formation of hexaferrites. The impact of Gd3+ substitutions was measured on all the lattice parameters. Lattice constants “a” and “c” were found between 5.879–5.891 Å and 43.185–43.620 Å, respectively. It was observed from the XRD analysis that with an increase in Gd–Co contents, the enhancement in the average crystallite size is noted. The thermal decomposition process was studied using TGA (thermogravimetric analysis), revealing that the precursor may give the ending product when...
Repulsive Casimir Forces
, M.Sc. Thesis Sharif University of Technology ; Bahmanabadi, Mahmoud (Supervisor) ; Taghizadeh Firouzjaee, Javad (Supervisor)
Abstract
It is well known that the fluctuations of electromagnetic fields in vacuum or in material media depend on the boundary conditions imposed on the fields. This dependence gives rise to forces which are known as Casimir forces, acting on the boundaries. Casimir forces between similar and disjoint objects such as two conducting or dielectric bodies are known in most cases to be attractive.¬¬ These forces are sometimes viewed as the macroscopic consequence of Van der Waals and Casimir-Polder attraction between molecules. In this thesis at first, calculation of Casimir forces in simple models were demonstrated. Then Van der Waals and Casimir-Polder forces have been explained in a unified theory...
Analysis of Artificial Dielectric Waveguides for Millimeter Wave Applications
, Ph.D. Dissertation Sharif University of Technology ; Rejaei, Behzad (Supervisor)
Abstract
Millimeter wave technology may prove to be one of the key technologies of the 21st century, covering a broad range of applications including high-speed telecommunication, wireless sensing, and ultra-fast digital computing. The ultimate (commercial) success of these technologies depends on the ability to integrate mm-wave circuitry on a chip, bringing about significant size and cost reduction. Traditionally, mm-wave systems have made extensive use of waveguides based on hollow- or dielectric-filled metallic cavities for the transfer and processing of signals. Cavity waveguides exhibit very low loss, but are not well-suited to high volume manufacturing or on-chip integration due to their...
Analysis of Losses in Articial Dilectric Waveguides at Mm-Wave Frequencies
, M.Sc. Thesis Sharif University of Technology ; Rejaei, Behzad (Supervisor)
Abstract
Today as various electronic and telecommunication devices like cell phones and PDAs are being popularized, MMIC technology is gaining a significant importance. One of the priorities of this technology is trying to miniaturize these popular devices. But reducing size of passive microwave components used in these devices requires microwave wavelength to decrease.Components fabricated by conventional deposition techniques aren’t thick enough to reduce the wavelength, so permittivities much higher than those of conventional dielectrics could be a possible solution. Artificial dielectric layers (ADL) can provide such high permittivities.So utilizing these layers can possibly reduce the size of...
Simulation and Assessment of Millimeter-Wave Reflectometry for Detection of Skin Cancers
, M.Sc. Thesis Sharif University of Technology ; Shishegar, Amir Ahmad (Supervisor)
Abstract
The goal of the research presented in this thesis is assessment of millimeter-wave (mm-wave) reflectometry as a potential method for non-invasive detection of skin cancers. The reasons for choosing mm-waves are lower penetration, higher resolution and technology maturity. The main work of this research is numerical simulation of reflection from skin and other media as well as reflection measurement of some skin-equivalent phantoms at mm-wave frequencies. By exposing the skin to mm-waves and studying the characteristics of the reflected wave malignant lesions are differentiated from benign and normal skin tissues. Since Oxygen molecules have strong attenuation peaks around 60 GHz band, this...
Numerical Simulation of DBD Plasma Actuator and Optimization for Separation Control
, M.Sc. Thesis Sharif University of Technology ; Mazaheri, Karim (Supervisor)
Abstract
Here we have used CFD to simulate the flow field around a DBD plasma active controller for flow control. Enhanced Electrostatic model is applied to model the plasma actuator, by solution of two elliptic equations to find electric field and charge density in whole flow field. So, it provided the body force by neglecting the magnetic forces in Lorentz equation. The body force is added to the momentum equation as a source term. A commercial software FLUENT is used for this simulation. To validate the algorithm, flow over a flat plate using DBD actuator is solved and results are compared with experimental and numerical results. Flow control around a cylinder with Reynolds number of 18,000 is...
Experimental Study of a DBD Plasma Actuators Location and Actuation Frequency on Flow Separation Control
,
M.Sc. Thesis
Sharif University of Technology
;
Ebrahimi, Abbas
(Supervisor)
;
Puoryousefi, Gholamhossein
(Co-Supervisor)
Abstract
This thesis investigates the stall control over an airfoil employing dual excitation of separated shear layers with DBD plasma actuators. This research is studied experimentally on the NACA 0015 airfoil at the angle of attack and Reynolds number of 14° and 300000, respectively. Two plasma actuators, one on the suction side just upstream the separation point and the other on the pressure side at the trailing edge, are exploited to control the baseline flow. Surface pressure distribution, as well as the dominant natural frequency associated with flow structures in the wake, are evaluated. Based on the active actuators, three controlled cases are considered in the present study. In the first...
Application of the characteristic green's function technique in closed-form derivation of spatial green's function of finite dielectric structures
, Article CEM 2013 - Computational Electromagnetics International Workshop ; number 6617132 , 2013 , Pages 54-55 ; 9781479914326 (ISBN) ; Shishegar, A. A ; Faraji Dana, R ; Sharif University of Technology
2013
Abstract
A closed-form spatial Green's function for finite dielectric structures is derived by using a combination of the characteristic Green's function (CGF) and rational function fitting method (RFFM). CGF-RFFM represents both of the discrete and continuous spectrum contributions efficiently by using the modified VECTFIT algorithm. To obtain more accurate results, reflection coefficient correction due to the surface waves (SWs) incident on the the end-facet is considered. The main advantage of this method lies in its speed as well as accuracy. Excellent agreements with the rigorous method of moments (MoM) are shown in several examples
Experimental investigation of the stability of the floating water bridge
, Article Physical Review E - Statistical, Nonlinear, and Soft Matter Physics ; Volume 88, Issue 3 , 2013 ; 15393755 (ISSN) ; Azizpour Lindi, S ; Amjadi, A ; Jafari, N ; Irajizad, P ; Sharif University of Technology
2013
Abstract
When a high voltage is applied between two beakers filled with deionized water, a floating bridge of water is formed in between exceeding the length of 2 cm when the beakers are pulled apart. Currently two theories regarding the stability of the floating water bridge exist, one suggesting that the tension caused by electric field in the dielectric medium is holding the bridge and the other suggesting surface tension to be responsible for the vertical equilibrium. We construct experiments in which the electric field and the geometry of the bridge are measured and compared with predictions of theories of the floating water bridge stability. We use a numerical simulation for estimation of the...
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) ; Saidi, M. S ; Sadeghi, A ; Sani, M
2013
Abstract
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...
Ultrawide band negative refraction based on moving media concept
, Article Applied Computational Electromagnetics Society Journal ; Volume 27, Issue 11 , November , 2012 , Pages 931-937 ; 10544887 (ISSN) ; Jafargholi, A ; Sharif University of Technology
2012
Abstract
The anomalous wave propagation in a homogeneous, isotropic and lossless medium that moves with a constant velocity along the axis of a rectangular waveguide; and its interesting properties lead us to the fact that the moving media may be regarded as double negative metamaterial (DNG). In this paper, the correct sign of the permittivity and permeability of an equivalent stationary media, for each TE and TM modes and for both low and high dielectric velocities are investigated and it is shown that this medium acts as a DNG material over specific frequency ranges