Search for: magnetism
Total 1408 records
Coupled mode theory of waveguides with conducting interfaces, Article Scientia Iranica ; Volume 10, Issue 4 , 2003 , Pages 426-435 ; 10263098 (ISSN) ; Rashidian, B ; Sharif University of Technology
Sharif University of Technology 2003
In this paper, the coupling coefficient of two waveguides with conducting interfaces is calculated analytically. It is shown that the control of interface charge densities via a transverse voltage leads to the control of the coupling. To derive the coupling coefficient, the basic Coupled Mode Theory (CMT) with paraxial approximation is improved to include the effect of conducting interfaces. The analysis is performed independently for TE and TM polarizations. Several direct applications of this effect including a multiplexer, a coupler and a modulator/switch and programmable grating are introduced. © Sharif University of Technology, October 2003
Optimization of the flux distribution in magnetic flux leakage Testing, Article Materials Evaluation ; Volume 68, Issue 3 , 2010 , Pages 360-364 ; 00255327 (ISSN) ; Ravanbod, H ; Sharif University of Technology
Many factors cause degeneration of the measured signal in magnetic flux leakage (MFL). One of these factors is non-uniformity of the magnetic flux inside the sample under test. Uniformity of the magnetic flux results in smoother and more predictable signals from various discontinuity types and also a reduction in the eddy current distortions induced because of the movement of the magnetizing yoke. The goal of this research is to find a near-optimal length for the magnetizing yoke. Toward this end, yokes with different lengths are simulated with the finite element method and the quality of the distribution of the flux lines inside the sample is studied. In this way a criterion for...
Dynamics of magnetic nano-flake vortices in Newtonian fluids, Article Journal of Magnetism and Magnetic Materials ; Volume 419 , 2016 , Pages 547-552 ; 03048853 (ISSN) ; Mohseni, S. M ; Khavasi, A ; Zibaii, M. I ; Movahed, S. M. S ; Jafari, G. R ; Sharif University of Technology
We study the rotational motion of nano-flake ferromagnetic disks suspended in a Newtonian fluid, as a potential material owing the vortex-like magnetic configuration. Using analytical expressions for hydrodynamic, magnetic and Brownian torques, the stochastic angular momentum equation is determined in the dilute limit conditions under applied magnetic field. Results are compared against experimental ones and excellent agreement is observed. We also estimate the uncertainty in the orientation of the disks due to the Brownian torque when an external magnetic field aligns them. Interestingly, this uncertainty is roughly proportional to the ratio of thermal energy of fluid to the magnetic energy...
Finemet nanocrystalline soft magnetic alloy: Investigation of glass forming ability, crystallization mechanism, production techniques, magnetic softness and the effect of replacing the main constituents by other elements, Article Journal of Magnetism and Magnetic Materials ; Volume 408 , 2016 , Pages 177-192 ; 03048853 (ISSN) ; Madaah Hosseini, H. R ; Sharif University of Technology
Finemet soft magnetic alloy has been in the focus of interest in the last years due to its high saturation magnetization, high permeability and low core loss. The great quantity of papers has been devoted to the study of its structural and magnetic properties, confirms this claim. This paper reviews the different researches performed on Finemet up to now. The criteria that should be satisfied in order to have the high glass forming ability in an alloy and also the techniques applied for production of Finemet ribbons, powders and bulk samples have been explained. In addition, the mechanism of devitrification, nanocrystallization and magnetic softness in this applicable magnetic alloy has been...
Comparing the physical properties of Pr/Gd and Pr/Ce substitutions in Ru(Gd 1.5Ce 0.5)Sr 2Cu 2O 10-δ, Article European Physical Journal B ; Volume 63, Issue 4 , 2008 , Pages 461-467 ; 14346028 (ISSN) ; Nikseresht, N ; Hadipour, H ; Akhavan, M ; Sharif University of Technology
We have compared the electrical and magnetic properties of Ru(Gd 1.5-x Pr x )Ce 0.5Sr 2Cu 2O 10-δ (Pr/Gd samples) with x = 0.0, 0.01, 0.03, 0.033, 0.035, 0.04, 0.05, 0.06, 0.1 and RuGd 1.5(Ce 0.5-x Pr x ) Sr 2 Cu 2O 10-δ (Pr/Ce samples) with x = 0.0, 0.01, 0.03, 0.05, 0.08, 0.1, 0.15, 0.2 prepared by the standard solid-state reaction technique. We obtained the XRD patterns for different samples with various x. The lattice parameters versus x for different substitutions have been obtained from Rietveld analysis. To determine how the magnetic and superconducting properties of these layered cuprate systems can be affected by Pr substitution, the resistivity, and magnetoresistivity, with H ext...
Simultaneous determination of theophylline and caffeine by proton magnetic resonance spectroscopy using partial least squares regression techniques, Article Analytical Sciences ; Volume 19, Issue 7 , 2003 , Pages 1079-1082 ; 09106340 (ISSN) ; Maesum, S ; Jalali Heravi, M ; Shamsipur, M ; Sharif University of Technology
Japan Society for Analytical Chemistry 2003
A 1H-NMR procedure based on an analysis of its data by a multivariate calibration method was conducted for the simultaneous determination of theophylline and caffeine in synthetic and real samples. Partial least squares regression (PLS) was chosen as the calibration method. The methyl signals of theophilline at 3.36 and 3.54 ppm that overlapped with those of caffeine were significant characteristics which were employed in this study for their analyses. The proposed method was successfully applied to recovery studies of theophylline and caffeine from real tablet samples
Magnetic nanoparticles entrapped in the cross-linked poly(imidazole/imidazolium) immobilized Cu(ii): An effective heterogeneous copper catalyst, Article RSC Advances ; Volume 4, Issue 87 , 2014 , Pages 46418-46426 ; ISSN: 20462069 ; Hosseini, S. H ; Zohreh, N ; Bennett, C ; Sharif University of Technology
Anchoring of copper sulfate in layered poly(imidazole-imidazolium) coated magnetic nanoparticles provided a highly stable, active, reusable, high loading, and green catalyst for the click synthesis of 1,2,3-triazoles via a one-pot cycloaddition of alkyl halide, azide, and alkyne (Cu-A3C). The catalyst was characterized by FTIR, TGA, TEM, SEM, XRD, EDAX, VSM and AAS. High selectivity, broad diversity of alkyl/benzyl bromide/chloride and alkyl/aryl terminal alkynes, and good to excellent yields of products were obtained using 0.7 mol% catalyst. The catalyst was readily recovered and reused up to 6 times without significant loss of activity
The correlations between processing parameters and magnetic properties of an iron-resin soft magnetic composite, Article Journal of Magnetism and Magnetic Materials ; Volume 305, Issue 1 , 2006 , Pages 147-151 ; 03048853 (ISSN) ; Madaah Hosseini, H. R ; Kianvash, A ; Sharif University of Technology
In this study, internal microstrain of an iron-resin composite produced by powder metallurgy has been calculated using the Williamson-Hall method. The effects of microstrain evolution during different processing conditions on magnetic properties such as coercive force and hysteresis loss have been investigated. The results show that there are regular and similar changes of coercivity and hysteresis loss. Both of these properties are directly dependant on the pinning effect of the internal microstrain against the movement of magnetic domain walls during magnetization process. © 2006 Elsevier B.V. All rights reserved
Itinerant electron transport in microscopically inhomogeneous magnetic fields, Article Journal of Magnetism and Magnetic Materials ; Volume 299, Issue 2 , 2006 , Pages 356-361 ; 03048853 (ISSN) ; Nogaret, A ; Atkinson, D ; Ghorbani, M ; Iraji Zad, A ; Sharif University of Technology
We report on magnetoresistance measurements in thin nickel films modulated by a periodic magnetic field emanating from micromagnetic arrays fabricated at the film surface. By increasing the strength of the magnetic potential using nickel and dysprosium micromagnets, we are able to quench the anisotropic magnetoresistance (AMR) in the film. © 2005 Elsevier B.V. All rights reserved
Considerations of Joule heating and radius reduction in umbral dots, Article Astronomy and Astrophysics ; Volume 407, Issue 2 , 2003 , Pages 761-767 ; 00046361 (ISSN) ; Sharif University of Technology
EDP Sciences 2003
The physical nature of bright features in sunspot umbra such as umbral dots (UDs) is not fully understood yet. Here, by accepting magnetic field reduction in the UDs, the Joule heating mechanism in the UDs is investigated. In this investigation, a UD model is assumed which is characterized by a) a reduced (possibly zero) magnetic field strength in the UD column relative to its surroundings, b) the electric current generated by magnetic field gradient at the boundary of the UD column can produce some heat, and c) when the radius of the UD - because of pressure reduction inside the column - becomes zero, the death of the UD will occur. The rate of radius reduction is estimated to be nearly 100...
Proceedings: Third International Conference on Magnetic and Superconducting Materials (MSM '03), Monastir, Tunisia, 1-4 September 2003, Book ; Akhavan, M.(Mohammad)
Proceedings of the first Regional Conference on Magnetic and Superconducting Materials (MSM-99); Tehran, Iran, 27-30 Sept. 1999, Book ; Akhavan, M ; Jensen, J ; Kitazawa, K
World Scientific 2000
Electrical transport properties of thin Ni films subjected to an array of nanomagnets, Article 2005 5th IEEE Conference on Nanotechnology, Nagoya, 11 July 2005 through 15 July 2005 ; Volume 1 , 2005 , Pages 15-18 ; 0780391993 (ISBN); 9780780391994 (ISBN) ; Nogaret, A ; Atkinson, D ; Ghorbani, M ; Iraji Zad, A ; Sharif University of Technology
IEEE Computer Society 2005
We report on magnetoresistance measurements in thin nickel films modulated by a periodic magnetic field emanating from micromagnetic arrays fabricated at the film surface. By increasing the strength of the magnetic potential using nickel and dysprosium micromagnets, we are able to quench the anisotropic magnetoresistance (AMR). We also observe mesoscopic magnetoresistance fluctuations, which possibly are related to the magnetic potential and size effects. ©2005 IEEE
Modeling and parametric studies of magnetic shape memory alloy–based energy harvester, Article Journal of Intelligent Material Systems and Structures ; Volume 29, Issue 4 , 2018 , Pages 563-573 ; 1045389X (ISSN) ; Rostami Najafabadi, H ; Askari Farsangi, M. A ; Sharif University of Technology
SAGE Publications Ltd 2018
This article presents a model to simulate the behavior of a magnetic shape memory alloy while harvesting vibratory energy. In this type of energy harvester, magnetic shape memory alloy element is placed in the air gap of a ferromagnetic core which conducts the magnetic flux. Two apparent coils are wound around a ferromagnetic core: one to produce bias magnetic field by passing a rectified electric current and the other to serve as an energy pickup coil. Applying compressive time-variant strain field to magnetic shape memory alloy element changes its dimensions and magnetic properties as well. Presence of the bias magnetic field returns magnetic shape memory alloy element to its initial state...
Modeling of self-controlling hyperthermia based on nickel alloy ferrofluids: Proposition of new nanoparticles, Article Journal of Magnetism and Magnetic Materials ; Volume 335 , 2013 , Pages 59-63 ; 03048853 (ISSN) ; Madaah Hosseini, H. R ; Wolff, M ; Sharif University of Technology
In order to provide sufficient heat without overheating healthy tissue in magnetic fluid hyperthermia (MFH), a careful design of the magnetic properties of nanoparticles is essential. We perform a systematic calculation of magnetic properties of Ni-alloy nanoparticles. Stoner-Wohlfarth model based theories (SWMBTs) are considered and the linear response theory (LRT) is used to extract the hysteresis loop of nickel alloy nanoparticles in alternating magnetic fields. It is demonstrated that in the safe range of magnetic field intensity and frequency the LRT cannot be used for the calculation of the area in the hysteresis for magnetic fields relevant for hyperthermia. The best composition and...
Performance verification of saturated IPM bearingless motors considering magnetic pull variation, Article Proceedings - 2016 IEEE International Power Electronics and Motion Control Conference, PEMC 2016, 25 September 2016 through 28 September 2016 ; 2016 , Pages 643-649 ; 9781509017980 (ISBN) ; Nasiri Gheidari, Z ; Rahman, A ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc 2016
Interior permanent magnet (IPM) bearingless motors are becoming a good choice for high-speed applications. In these motors, reducing the thickness of the PM leads to the increase of the radial forces which affects the demagnetizing fields. Various types of PM motors have so far been recommended for enhancement of the radial forces and torque. In the proposed IPM motor the d-axis flux-linkage and the q-axis torque component are raised due to the armature reaction and this saturates the stator teeth. In addition, the magnetic attraction force generated by displacement force depends on the armature reaction. The mathematical model of IPM bearingless motor based on the dq transformation,...
Numerical simulation of magnetic convection ferrofluid flow in a permanent magnet–inserted cavity, Article Journal of Magnetism and Magnetic Materials ; Volume 442 , 2017 , Pages 270-278 ; 03048853 (ISSN) ; Behshad Shafii, M ; Sharif University of Technology
The magnetic convection heat transfer in an obstructed two-dimensional square cavity is investigated numerically. The walls of the cavity are heated with different constant temperatures at two sides, and isolated at two other sides. The cavity is filled with a high Prandtl number ferrofluid. The convective force is induced by a magnetic field gradient of a thermally insulated square permanent magnet located at the center of the cavity. The results are presented in the forms of streamlines, isotherms, and Nusselt number for various values of magnetic Rayleigh numbers and permanent magnet size. Two major circulations are generated in the cavity, clockwise flow in the upper half and...
Ferrofluid droplet formation from a nozzle using alternating magnetic field with different magnetic coil positions, Article Journal of Magnetism and Magnetic Materials ; Volume 498 , 2020 ; Bijarchi, M. A ; Shafii, M. B ; Sharif University of Technology
Elsevier B.V 2020
Ferrofluid has been used in many fields, such as microfluidics, droplet formation, and heat transfer, due to its potential to be attracted in the presence of a magnetic field. Droplet formation, itself, has many applications such as emulsions, 3D micro-printers, MEMS, and electro-sprays. In this study, the mechanism of ferrofluid droplet formation from the nozzle in the presence of an alternating magnetic field was investigated. The magnetic coil was fixed at different angles with respect to gravity and the effect of the alternating magnetic field and the angle of the magnetic coil axis with respect to gravity on the produced droplet volume, satellite droplet, and droplet formation frequency...
Numerical investigation of effects of uniform magnetic field on heat transfer around a sphere, Article International Journal of Heat and Mass Transfer ; Volume 114 , 2017 , Pages 703-714 ; 00179310 (ISSN) ; Molaei Dehkordi, A ; Abbasi, F ; Sharif University of Technology
Elsevier Ltd 2017
In this article, ferrohydrodynamic forced-convection heat transfer from a heated sphere embedded in a ferrofluid in the presence of the uniform external magnetic field has been studied numerically for the first time over a wide range of Reynolds number value, nanoparticle diameter, particle volume fraction, and magnetic field intensity. Despite the uniform external magnetic field applied, the internal magnetic field near the sphere could be nonuniform due to the considerable difference between the relative magnetic permeability of the sphere and the surrounding medium. Kelvin body force arises from this nonuniformity and induces vortexes near the sphere. These vortexes disturb the boundary...
Ferrofluid flow and heat transfer from a sphere in the presence of nonuniform magnetic fields, Article Journal of Heat Transfer ; Volume 141, Issue 11 , 2019 ; 00221481 (ISSN) ; Molaei Dehkordi, A ; Sharif University of Technology
American Society of Mechanical Engineers (ASME) 2019
In this article, the effects of nonuniform magnetic fields on the hydrodynamics and heat transfer from a heated sphere to its surrounding ferrofluid flow have been investigated. Kelvin body forces originate from the nonuniformity of the applied magnetic field and can generate the vortices behind the sphere leading to a considerable change in the velocity and temperature fields. The applied magnetic field disturbs the thermal boundary layer and decreases heat-transfer resistance, leading to a significant enhancement in the heat-transfer coefficient. Variations of the local and average Nusselt number value (Nu), separation angle, recirculation length, and drag coefficient were considered to...