Search for: electrical-resistivity
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    Vibration effect on electrical resistance fluctuations in electrical connectors

    , Article Engineering Solid Mechanics ; Volume 6, Issue 4 , 2018 , Pages 299-306 ; 22918744 (ISSN) Behzad, M ; Darvish Gohari, H ; Mohammadi Dehabadi, A. A ; Sharif University of Technology
    Growing Science  2018
    Proper functioning of electrical connectors used in high oscillation is of great importance. Vibrations in connector pins cause stress and electrical resistance variations in the contact surface. In the present paper, the impacts of vibrational loads on electrical connectors is being modeled using the finite element method, and the electrical resistance oscillations of the connectors will be examined. Ultimately, the parameters affecting the electrical resistance oscillations of contacts will be determined and their relations with oscillations in electrical resistance are specified as well. © 2018 by the authors; licensee Growing Science, Canada, 2018 Growing Science Ltd. All rights reserved... 

    An Investigation into the Production and Properties of Lead-Free Solder Alloy Sn-3.5Ag

    , M.Sc. Thesis Sharif University of Technology Ghadi, Saman (Author) ; Karimi Taheri, Ali (Supervisor)
    This study was conducted in order to investigate on production and propeties of lead free solder alloy. For this purpose, Sn-Ag alloy with 3.5 weight percent of silver and sn-3.5Ag-0.7Cu at eutectic composition were produced with casting procedure.Single-lap Specimens were used to simulate real solder joints with the solder reflowed between two pure Cu substrate.Microstructural characterization, electrical resistance measurements and shear-tension test were performed.A deacrease of electrical resistance was observed in produced alloys in comparison with Sn-Pb . Experimental results showed that mechanical properties of produced alloys was better than common pb content alloy.The effect of... 

    Fabrication of SiC body by microwave sintering process

    , Article Journal of Materials Science: Materials in Electronics ; Volume 28, Issue 7 , 2017 , Pages 5675-5685 ; 09574522 (ISSN) Ahmadbeygi, S ; Khodaei, M ; Nemati, A ; Yaghobizadeh, O ; Sharif University of Technology
    Springer New York LLC  2017
    In the present study, SiC samples with 3, 5, 7.5 and 10 wt% Al2O3–Y2O3 as additives were made by powder metallurgy method, then sintering was performed by microwave-assisted process. β–SiC samples sintering was performed for 100 min. The highest sintered relative density 91.06% was achieved at 10 wt% additives content. The maximum values of hardness and toughness were up to 23.3 GPa and 6.14 MPa.m− 1/2. α–SiC and α–SiC/β–SiC samples sintering was performed for 120 min. The maximum value of density and hardness were up to 96.38% T.D and 24.88 GPa in α–SiC with 7.5 wt% additives, whereas the highest toughness was achieved at 10 wt% additives content in β–SiC samples. The α–SiC samples... 

    Friction Stir Soldering of Copper Coated Graphite-Copper Joints by Sn-Pb Solder

    , M.Sc. Thesis Sharif University of Technology Ebrahimian, Ali (Author) ; Kokabi, Amir Hossein (Supervisor)
    Friction stir soldering (FSS) or brazing (FSB) as an emerging joining process, was first developed to resolve some shortcomings in FSLW and FSSLW such as excessive IMC layer thickness and confined bond area. Although it has advantages over conventional furnace soldering and/or brazing, including localized heating, less detrimental thermal effects on the substrates and capability to reduce the amount of voids at the joint interface. The aim of this study is to investigate the effects of rotational speed, traverse speed and plunge depth of the pinless tool on the shear strength and electrical resistivity of the copper-coated graphite-copper FSSed joints with the aid of Sn-37Pb solder alloy. At... 

    The effects of a magnetic barrier and a nonmagnetic spacer in tunnel structures

    , Article Journal of Physics Condensed Matter ; Volume 16, Issue 25 , 2004 , Pages 4455-4463 ; 09538984 (ISSN) Shokri, A. A ; Saffarzadeh, A ; Sharif University of Technology
    The spin-polarized transport is investigated in a new type of magnetic tunnel junction which consists of two ferromagnetic electrodes separated by a magnetic barrier and a nonmagnetic metallic spacer. Based on the transfer matrix method and the nearly-free-electron approximation the dependence of the tunnel magnetoresistance (TMR) and electron-spin polarization on the nonmagnetic layer thickness and the applied bias voltage are studied theoretically. The TMR and spin polarization show an oscillatory behaviour as a function of the spacer thickness and the bias voltage. The oscillations originate from the quantum well states in the spacer, while the existence of the magnetic barrier gives rise... 

    Self aligned passivation of Cu in Cu/Cr, Cu/V and Cu/Ta multilayers

    , Article 12th International Conference on Microelectronics, ICM 2000, 31 October 2000 through 2 November 2000 ; Volume 2000-October , 2000 , Pages 209-212 ; 9643600572 (ISBN) Iraji Zad, A ; Vashaei, Z ; Mahdavi, S. M ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2000
    We compare Cu/M/SiO2 (M=Cr,V and Ta) multilayers that were deposited on Si substrates. Sample resistance measurements were carried out during annealing in 80% N2+20% H2, N2 and Ar environments. Resistivity measurements, SEM observations, RBS and AES spectroscopies from annealed samples showed good diffusion barrier properties for Cr and V but rather poor properties for Ta buffer layers. This is due to the amorphous nature of Cr films and formation of a continuous Cu overlayer. SEM observation also showed granular structure for Cu/V and Cu/Ta with grain sizes of about 500 and 1000 Å respectively. However, shallow nitrogen implantation in Cu/V samples and DC biasing for Cu/Ta layers during... 

    Effect of graphene and process parameters on mechanical performance and electrical resistance of aluminum to copper friction stir joint

    , Article Materials Research Express ; Volume 6, Issue 4 , 2019 ; 20531591 (ISSN) Montazerian, M. H ; Movahedi, M ; Jondi, M. R ; Sharif University of Technology
    Institute of Physics Publishing  2019
    Effects of graphene, tool rotational speed and pass number were studied on the reliability and electrical resistance of the aluminum to copper friction stir welds. Addition of graphene was an effective solution to overcome the increase in the electrical resistance of the aluminum/copper joints. Indeed, presence of graphene decreased the electrical resistance of the joints to the values comparable with that of the copper base metal. However, joint tensile strength was not affected significantly by graphene. Decrease in the tool rotational speed improved the dispersion of the graphene particles and tensile strength, while reduced the electrical resistance. Tensile strength of the joint reached... 

    Data acquisition and resistance measurements using a simple program

    , Article Scientia Iranica ; Volume 14, Issue 5 , 2007 , Pages 467-473 ; 10263098 (ISSN) Golnabi, H ; Azimi, P ; Poseh, G. H ; Sharif University of Technology
    Sharif University of Technology  2007
    The goal of this paper is to describe a simple method for the automated data acquisition and analysis of data taken by programmable instruments. Device controls and communication method are explained and some typical illustrative examples showing the potential applications of the method in real experiments are presented. This method offers a quick and flexible way to control many instruments by using a multi-device arrangement of a stacking method in a parallel operation. The General-Purpose Interface Bus (GPIB) is used here for remote control of the devices. By using Excel and Visa interactive programs and using GPIB interface, easy communication and data transfer between instruments and a... 

    The Effect of Shock and Vibration Loads on Disconnection and Fluctuations of Electrical Current in Connectors

    , M.Sc. Thesis Sharif University of Technology Darvish Gohari, Hamed (Author) ; Behzad, Mehdi (Supervisor)
    Electrical connectors that used in high speed systems interrupt the connection at the effect of Inertia. Also connectors should be able to work in high vibration conditions without any problems. Vibration of the connector pins can reduce the contact area or even remove it at very short time intervals, which lead to increase connector resistance or disconnection of instantaneous current. These current fluctuations will result in unpredictable performance disturbanceof the electrical system in very sensitive systems and therefore it should be avoided. In this Project, impacts of shock and vibration loads on the connectors is modeled by using FEM and with consideration of this model, connection... 

    Electrical behaviour of glass/ carbon- phenolic conductive hybrid composite woven used in electrostatics precipitator filter

    , Article International Journal of Electrochemical Science ; Vol. 9, issue. 11 , 2014 , p. 6416-6430 Neyestanak, A. A. L ; Nazari, S. A ; Sadeghbeigi, N ; Karimzadeh, A ; Sharif University of Technology
    Electrical behavior of hybrid conductive composites made of phenolic resin, graphite woven, glass woven and graphite nano powder has been studied for the first time in the present research to apply as collecting plates in electro static precipitators. To this purpose, two types of four-layer composites smeared with phenolic resin by different amounts of graphite nano powder then produced at 120°C and 200 bars with proper curing cycle. Finally, electrical resistivity of all the plates undergoing impact loading after different rapping cycles was measured by means of a repetitive rapping tester system particularly manufactured for this task. This study performs changes in mechanical behavior of... 

    Scanning tunneling spectroscopy of porous silicon in presence of methanol

    , Article Sensors and Actuators, B: Chemical ; Volume 120, Issue 1 , 2006 , Pages 172-176 ; 09254005 (ISSN) Rahimi, F ; Iraji zad, A ; Vaseghinia, S ; Sharif University of Technology
    In this research, we used the scanning tunneling spectroscopy (STS) technique to probe the local electrical properties of the surface of meso-porous silicon and its substrate, including local density of states (DOS) in air and in methanol environment to increase our knowledge of sensing phenomena. Meso-porous silicon was prepared on p+-type Si which has high sensitivity toward methanol. Observations revealed that while the surface electrical properties of p+-type Si have not sensible change toward methanol, average local density of state of the porous layer increases after the exposure to methanol especially in the E < EF region. Moreover, large number of surface states is produced in band... 

    Effective factors on Pd growth on porous silicon by electroless-plating: Response to hydrogen

    , Article Sensors and Actuators, B: Chemical ; Volume 115, Issue 1 , 2006 , Pages 164-169 ; 09254005 (ISSN) Rahimi, F ; Iraji zad, A ; Sharif University of Technology
    Porous silicon samples obtained from p+-type silicon wafers were impregnated with Pd by electroless process in different conditions. Scanning electron microscopy was used to study the change in the features of the surface after palladium plating. Results showed how the factors like Pd-salt concentration, HCl concentration, temperature of the electroless solution and the time of process affect on the growth and nucleation of Pd particles. Observations demonstrated that illumination-assisted process and pre-oxidation of the surface before process have drastic effect on the growth of palladium. Variation of the electrical resistance in the presence of diluted hydrogen at room temperature... 

    From continuous to quantized charging phenomena in few nanocrystals MOS structures

    , Article 11th International Autumn Meeting on Gettering and Defect Engineering in Semiconductor Technlogy, GADEST 2005, Giens, 25 September 2005 through 30 September 2005 ; Volume 108-109 , 2005 , Pages 25-32 ; 10120394 (ISSN); 3908451132 (ISBN); 9783908451136 (ISBN) BenAssayag, G ; Shalchian, M ; Grisolia, J ; Bonafos, C ; Atarodi, S. M ; Claverie, A ; Sharif University of Technology
    Trans Tech Publications Ltd  2005
    In this paper, we present a study on the contribution of silicon nanocrystals to the electrical transport characteristics of large (100 μm × 100 μm) and small (100 nm × 100 nm) metaloxide-semiconductor (MOS) capacitors at room temperature. A layer of silicon nanocrystals is synthesized within the oxide of these capacitors by ultra-low energy ion implantation and annealing. Several features including negative differential resistance (NDR), sharp current peaks and random telegraph signal (RTS) are demonstrated in the current-voltage and current-time characteristics of these capacitors. These features have been associated to charge storage in silicon nanocrystals and to the resulting Coulomb... 

    The Pr and oxygen correlation in the GdPr123 system

    , Article Modern Physics Letters B ; Volume 16, Issue 25 , 2002 , Pages 943-953 ; 02179849 (ISSN) Khosroabadi, H ; Daadmehr, V ; Akhavan, M ; Sharif University of Technology
    We prepared single-phase polycrystalline Gd1-xPrx Ba2Cu3O7-δ samples with x = 0, 0.10, 0.15, and 0.20. The deoxygenation process of these samples was performed by an annealing method. Electrical resistivity measurements revealed depression of the transition temperature with the increase of x and δ. We calculated the hole concentration in the CuO2 plane for different values of x and δ. A linear dependence of transition temperature and hole concentration in the CuO2 plane was found as a function of 2δ + x. It is proposed that a combination of the localization and filling of holes should be considered as the effective mechanisms for the appearance of the Pr anomaly in HTSCs  

    A low-voltage low-power switched-capacitor filter using a new transistor configuration

    , Article 12th International Conference on Microelectronics, ICM 2000, 31 October 2000 through 2 November 2000 ; Volume 2000-October , 2000 , Pages 99-102 ; 9643600572 (ISBN) Lotfi, R ; Atarodi, S. M ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2000
    A novel cascode configuration previously presented as a high output resistance load (Fujimori and Sugimoto, 1998) has been investigated and utilized for amplification to achieve higher gain and bandwidth by the authors (Lofti and Atarodi, Proc. ICEE'00, vol.1, pp.83-8, 2000). A low-voltage single-stage opamp using this configuration is designed. Finally, based on this idea a 1.5-V offset- and gain-compensated 5th order switched-capacitor low pass filter with only 150 μA current consumption in a 0.8 μm process is designed. © 2000 IEEE  

    Physical properties of sputtered amorphous carbon coating

    , Article Journal of Alloys and Compounds ; Volume 513 , 2012 , Pages 135-138 ; 09258388 (ISSN) Yari, M ; Larijani, M. M ; Afshar, A ; Eshghabadi, M ; Shokouhy, A ; Sharif University of Technology
    In this study the effect of deposition temperature and thickness on the physical properties of carbon films deposited by magnetron sputtering PVD was investigated. The results of Raman spectra and grazing incidence XRD (GIXRD) patterns show that the graphitization increases by increasing the deposition temperature. There is a change in deposition mechanism at 400 °C from amorphous carbon deposition to nano-structured graphite deposition. Also by increasing substrate temperature the electrical resistance of carbon films reduces significantly up to 300 °C and then remains largely constant. High intrinsic compressive stress in low temperature deposited carbon films causes cracks and... 

    , M.Sc. Thesis Sharif University of Technology Adibi, Behnam (Author) ; Karimi Taheri, Ali (Supervisor)
    This study was conducted in order to investigate the effect of difference in electrical resistivity between low carbon steel and austenitic stainless steel on the physical and mechanical properties and fracture mode of dissimilar resistance spot welds of these alloys. For this purpose, plastic deformation using constrained groove pressing combined with rolling applied to low carbon steel in three levels of 40%, 156% and 272%. Microstructural characterization, micro-hardness measurements and shear-tension test were performed. It was shown that by increasing the pre-strain in low carbon steel its electrical resistivity increases from 13.08 μΩ.cm to 19.5 μΩ.cm and because of reduction of... 

    Theoretical and Experimental Investigation of Cold Roll Welding for Production of Aluminum Clad Steel Sheet

    , Ph.D. Dissertation Sharif University of Technology Danesh Manesh, Habib (Author) ; Karimi Taheri, Ali (Supervisor)
    Aluminum coated steel sheet is an excellent composite material in which; the strength and economy of steel and durability of aluminum are combined. This material is produced by several methods. However, there are two main technologies to produce aluminized steel sheets: 1) the hot dip method and 2) the aluminum clad method (cold roll welding process). The hot dip method is most widely used for producing the aluminum coated steel. The aluminum coated steel sheet manufactured by this method is believed to be inferior to an aluminum sheet with respect to surface appearance, corrosion resistance and formability of the coated metal. Consequently, the aluminum clad steel method is one of the most... 

    Effect of iron Powder in Electrical Conductivity of Concrete

    , M.Sc. Thesis Sharif University of Technology Ghanbari Chemazketi, Ali (Author) ; Joghataie, Abdolreza (Supervisor)
    Performance and mechanical properties of concrete such as tensile strength, compressive strength, conductivity, etc change with creation and emission of cracks. As health monitoring of important structures is a vital subject that demands a large amount of budget annualy. Studying problems and disadvantages of concrete is one of the most important branches of research.
    There are many ways to detect damage in concrete. Electrical resistance method that has been used in this thesis. In this study, an instrument called Risistivity Meter is used to measuring the electrical conductivity. This instrument measured the electrical conductivity, that it can be appropriate way to detect cracks... 

    Upset Resistance Welding of Aluminium to Steel

    , M.Sc. Thesis Sharif University of Technology Abiri, Milad (Author) ; Kookabi, Amir Hossein (Supervisor) ; Movahedi, Mojtaba (Supervisor)
    Aluminum and steel are the most utilized metals in industry and joining of them has many applications including heat exchangers and parts in aluminum extraction process. In this research, Upset Resistance Welding of aluminum to stainless steel was studied. In this regard, the effect of current intensity, time of welding, in-situ post-heating operation and post-heating operation in the furnace were investigated on the microstructure, mechanical properties and electrical resistance of welds. The currents of 2.25, 2.30 and 2.35 kA and times of 55, 60 and 65 cycles were applied for welding. Then in-situ post-heating conducted under currents of 1.75, 2.25 and 2.75 kA and 10 cycles on the sample...