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    Anomaly in current distribution of multiwall carbon nanotube bundles at high frequencies

    , Article 14th IEEE International Conference on Nanotechnology, IEEE-NANO 2014 ; 2014 , pp. 702-705 ; ISBN: 9781479956227 Farahani, E. K ; Sarvari, R ; Sharif University of Technology
    In this paper, for the first time, current distribution inside multiwall carbon nanotube (MWCNT) bundles is studied in the high frequency range in which resistance becomes saturated. It is shown that current distribution of MWCNT bundles in this range is not strictly decreasing vs. distance from surface as in Cu wires  

    A divide-by-3 frequency divider for I/Q generation in a multi-band frequency synthesizer

    , Article APCCAS 2008 - 2008 IEEE Asia Pacific Conference on Circuits and Systems, Macao, 30 November 2008 through 3 December 2008 ; 2008 , Pages 1383-1386 ; 9781424423422 (ISBN) Saeedi, S ; Atarodi, M ; Sharif Bakhtiar, M ; Sharif University of Technology
    A divide-by-3 frequency divider for Inphase and Quadrature (I/Q) LO signal generation in a multi-band frequency synthesizer is presented. Using divisor numbers other than powers of 2 (2n) for quadrature signal generation, reduces the required frequency range of the VCO in multi-band frequency synthesizers. The divide-by-3 circuit is designed in a 0.18um CMOS technology. © 2008 IEEE  

    Experimental Investigation of Buzz Frequency on an Axisymmetric Supersonic Air Intake Using Pressure Distribution on the Wind Tunnel Wall

    , M.Sc. Thesis Sharif University of Technology Bagheri, Maryam (Author) ; Soltani, Mohammad Reza (Supervisor) ; Farahani, Mohammad (Co-Advisor)
    Supersonic intakes with mixed compression has an appropriate performance in the critical point, but in the subcritical performance, when inlet mass flow rate is reduced to a certain amount, a self-sustained instability occurs in the flow. In this case, instability appears in the form of shock waves system oscillation which is called Buzz phenomenon. An axisymmetric supersonic air intake with mixed compression which is designed for a Mach number of 2 has been investigated experimentally in order to study buzz frequency. The intake has been experimented in different Mach numbers, angles of attack and mass flow rates. Besides, the intake with wind tunnel wall has been modeled and analyzed in... 

    Investigation of the Ion Migration Mechanism and its Effect on the Slow Response of Perovskite Solar Cells

    , Ph.D. Dissertation Sharif University of Technology Ebadi Garjan, Firouzeh (Author) ; Taghavinia, Nima (Supervisor) ; Mohammadpour, Raheleh (Supervisor)
    In recent years, organo-metal perovskite solar cells have attracted remarkable attention due to their low cost manufacturing method as well as the rapid growth of efficiency. Despite the fast growing efficiency of organo-metal perovskite solar cells, there are big challenges around their low stability under real operational condition. In addition to extrinsic parameters like oxygen and humidity, intrinsic instability of perovskite rises mainly from ion migration in perovskite film. In order to understand the ion migration and its effect on photovoltaic parameters of the devices, appropriate characterizations and analysis are needed. Since ions are much slower compare to electrons, their... 

    Rattle noise source prediction for instrument panel of a car using hybrid sea-fem analysis

    , Article 20th International Congress on Sound and Vibration 2013, ICSV 2013 ; Volume 4 , July , 2013 , Pages 2883-2890 Beigmoradi, S ; Jahani, K ; Ramezani, A ; Hajabdollahi, H ; Sharif University of Technology
    International Institute of Acoustics and Vibrations  2013
    Squeak and rattle (S&R) noises are important in-cabin sources of annoyance for occupants. Originally, S&R is generated as a result of colliding and slamming of car's trim and body structure which in turn occurs because of the dynamic displacements of components excited by road and power-train. Squeak noise is interpreted as periodic stick and slip phenomena in the contact boundary of two neighbor surfaces. While rattle noise is the emitted noise when adjacent surfaces collide and impact. Squeak noise takes place at low frequency while rattle phenomenon happens in high-frequency range, even though the excitation sources (road and power-train line) works in low frequency range. In practice,... 

    Panel contribution analysis for a sedan car using numerical simulations

    , Article 20th International Congress on Sound and Vibration 2013, ICSV 2013 ; Volume 4 , 2013 , Pages 2891-2898 ; 9781629931500 Jahani, K ; Beigmoradi, S ; Ramezani, A ; Hajabdollahi, H ; LMS ; Sharif University of Technology
    International Institute of Acoustics and Vibrations  2013
    These days, the pace of utilizing CAE tools is increasing with an eye to the vehicle development time and cost considerations. This paper deals with the NVH virtual analyses performed for a trimmed body of a B-segment sedan car. Since the main source of annoyance in low frequency range is the booming noise, the NVH diagnoses are performed by FEM tools. Firstly, the finite element model of the car is generated and this is followed by the modal analysis simulations for the car and cavity models in order to investigate the frequency attributes of the car and identify the NVH characteristics of body structure and acoustic cavity. Afterwards, noise transfer function (NTF) analyses are performed... 

    High quality factor RF inductors using low loss conductor featured with skin effect suppression for standard CMOS/BiCMOS

    , Article Proceedings - Electronic Components and Technology Conference, 31 May 2011 through 3 June 2011 ; June , 2011 , Pages 163-168 ; 05695503 (ISSN) ; 9781612844978 (ISBN) Iramnaaz, I ; Sandoval, T ; Zhuang, Y ; Schellevis, H ; Rejaei, B ; Sharif University of Technology
    Integrated on-chip inductors with high quality factors are demonstrated using a low loss artificial conductor technology. This concept is based on an artificial layered meta-material comprising a bi-layered Ni 80Fe 20/Cu superlattice. By properly tailoring the thickness ratio between the non-magnetic and magnetic metallic layers, the skin effects can be effectively suppressed within a wide frequency range, and can be tuned to a minimum at the frequency of interest up to 67 GHz. The quality factor has been increased by 41% of a 2nH inductor at 14.5GHz. The bandwidth of skin effect suppression is obtained between 10-18 GHz  

    Design of ultra-broadband graphene absorber using circuit theory

    , Article Journal of the Optical Society of America B: Optical Physics ; Volume 32, Issue 9 , 2015 , Pages 1941-1946 ; 07403224 (ISSN) Khavasi, A ; Sharif University of Technology
    I propose a novel method for designing a broadband THz absorber by using periodic arrays of graphene ribbons on a Salisbury-screen-like structure. The recently proposed analytical circuit model of graphene arrays is used for obtaining analytical expressions for the input admittance of the proposed device. The input admittance is then adjusted to be closely matched to the free space in a wide frequency range. Consequently, it is demonstrated that a bandwidth of 90% absorption can be extended up to 100% of the central frequency with only one layer of patterned graphene  

    Ultra-Sharp Transmission Resonances in Periodic Arrays of Graphene Ribbons in TE Polarization

    , Article Journal of Lightwave Technology ; Volume 34, Issue 3 , 2016 , Pages 1020-1024 ; 07338724 (ISSN) Khavasi, A ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc 
    When illuminated by TM polarized waves, periodic arrays of graphene ribbons are known to exhibit plasmonic resonances due to their dual inductive-capacitive nature. It is demonstrated here that even in TE polarization, resonances can be observed in these structure. These resonances, which are of nonplasmonic origin, are explained by means of a circuit model. It is shown that, for a certain frequency range, arrays of graphene ribbons have both capacitive and inductive properties, which lead to an ultra-sharp inductor-capacitor resonance. The banw idth of this resonance can be as narrow as ∼0.0002 nm at a wavelength of 630 nm. The resonance can also be viewed as the grating excitation of a TE... 

    Wideband planar log-periodic antenna

    , Article 2007 IEEE International Workshop on Antenna Technology: Small and Smart Antennas Metamaterials and Applications, iWAT 2007, Cambridge, 21 March 2007 through 23 March 2007 ; 2007 , Pages 331-334 ; 1424410886 (ISBN); 9781424410880 (ISBN) Tajdini, M. M ; Shahabadi, M ; Sharif University of Technology
    A compact planar wideband microstrip antenna is introduced. The antenna is a log-periodic antenna with 7 dipole elements. The antenna is designed to function in the frequency range of 500 to 700 MHz. It has a dimension of 268 mm by 145 mm by 3 mm. The matching is better than -10 dB in the working bandwidth. The proposed antenna generates linear polarization. Its maximum gain is 4.5 dB at the central frequency. It provides a low-cost alternative to the conventional Yagi-Uda TV antennas. © 2007 IEEE  

    Design method for a reconfigurable CMOS LNA with input tuning and active balun

    , Article AEU - International Journal of Electronics and Communications ; Vol. 69, issue. 1 , January , 2014 , p. 424-431 Akbar, F ; Atarodi, M ; Saeedi, S ; Sharif University of Technology
    A method to design a tunable low noise amplifier (LNA) for multiband receivers is proposed. This paper also presents a single-ended to differential conversion (S2DC) topology which improves the LNA linearity without degrading its noise performance. Combining input tuning with S2DC in a single stage reduces power consumption of the LNA and decreases effects of supply noise. An LNA has been designed based on the proposed method for 2.3-4.8 GHz in a 0.18 μm CMOS technology. Simulations show an IIP3 of -3.2 dBm, a less than 3.7 dB noise figure (NF), a voltage gain of 24 dB in the whole frequency range. The LNA draws 13.1 mW from a 1.8 V supply. The results indicate that the proposed tuning... 

    Investigation of water electrical parameters as a function of measurement frequency using cylindrical capacitive sensors

    , Article Measurement: Journal of the International Measurement Confederation ; Volume 46, Issue 1 , 2013 , Pages 305-314 ; 02632241 (ISSN) Golnabi, H ; Sharifian, M ; Sharif University of Technology
    In this study electrical properties of different water liquids at frequency range of 100-2000 Hz are investigated by using the short invasive and non-invasive cylindrical capacitive sensors (CCSs). Operation of the capacitance measurement module for such probes is based on the auto balancing bridge method. Comparison of the measured capacitances and measured resistances for different water liquids shows decrease by increasing the frequency. In another study the dielectric constant of distilled water, mineral water, tap water and salt water are measured. The effects of the frequency on the resistivity, permittivity and conductance of the different water liquids are also investigated  

    An ultra-wideband 3-dB quadrature hybrid with multisection broadside stripline tandem structure

    , Article Lecture Notes of the Institute for Computer Sciences, Social-Informatics and Telecommunications Engineering ; Volume 77 LNICST , 2012 , Pages 672-681 ; 18678211 (ISSN) ; 9783642351549 (ISBN) Javadzadeh, S. M. H ; Majedi, S. M. S ; Farzaneh, F ; Sharif University of Technology
    Design of an Ultra-Wideband 3-dB quadrature (90°) Hybrid using ADS and HFSS softwares plus Measurement report are presented. Simultaneous Use of these two softwares lead to fast and accurate design procedure. The coupler is realized in broadside stripline and with the connection of coupled regions in tandem structure. The measured data agrees well with the expected values from simulations, and shows a good ultra wide bandwidth response over the frequency range of 1-10 GHz. Measurements showed an amplitude unbalance of ±1.5 dB, a phase unbalance of 90°±7° , and an isolation and a return loss characteristics of more than 14 dB over the frequency of 1 to 10 GHz  

    Ultrasound dosimetery using microbubbles

    , Article IFMBE Proceedings, 20 June 2011 through 23 June 2011 ; Volume 35 IFMBE , June , 2011 , Pages 359-362 ; 16800737 (ISSN) ; 9783642217289 (ISBN) Rezayat, E ; Zahedi, E ; Tavakkoli, J ; Sharif University of Technology
    In this paper, a new technique based on nonlinear resonance of microbubbles is investigated in order to estimate the amplitude of an ultrasound wave pressure field. First, the existing theoretical model is reviewed. Then, an experimental setup consisting of a bubble generator and transmitting/receiving ultrasound transducers operating in the 1 MHz frequency range is described. The effect of background noise is also taken into account. Results show that the second harmonic oscillations are detectable, paving the way to develop a quantitative method for in vivo calibration of ultrasound waves  

    Electromagnetic interference shielding effectiveness of Al/SiC composite foams

    , Article Journal of Materials Science: Materials in Electronics ; Volume 26, Issue 10 , 2015 , Pages 7530-7536 ; 09574522 (ISSN) Kheradmand, A. B ; Lalegani, Z ; Sharif University of Technology
    Springer New York LLC  2015
    Closed cell aluminum foams are fabricated by using the casting method. The electromagnetic interference (EMI) shielding effectiveness of foams are investigated in the frequency range of 1.44–5 and 8–12 GHz (X band).The shielding materials are made of Al foam with the addition of different concentrations of SiC (5, 10, 15 wt%). Results show that the Al/SiC composite foams have good shielding effectiveness. EMI shielding effectiveness of samples generally increased with increasing porosity and with the increasing of SiC content. The sample with 15 wt% SiC had shielding effectiveness values of up to 150 dB  

    Frequency response features of a multi-objective wind turbine transformer design

    , Article 24th Iranian Conference on Electrical Engineering, 10 May 2016 through 12 May 2016 ; 2016 , Pages 643-648 ; 9781467387897 (ISBN) Elhaminia, P ; Vakilian, M ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc 
    A wind turbine transformer internal resonance, excited by high frequency transients i.e.; under its energization through a short length of cable, is considered to obtain a proper transformer design method. A multi-objective optimum design method (using TOC and inrush current energy factor as objective functions) is employed and the optimal Pareto solutions for this design are derived. Selected design from the Pareto optimal solutions are then modeled using the lumped RLC ladder network, valid over a wide frequency range. The obtained frequency responses are then compared with each other to investigate the effect of multi-objective design on different aspects of the transformer winding... 

    Design of a reconfigurable front end for a multistandard receiver for the frequency range of 800 MHz to 2.5 GHz

    , Article International Journal of Circuit Theory and Applications ; Volume 46, Issue 6 , 2018 , Pages 1144-1165 ; 00989886 (ISSN) Zare Fatin, G ; Koozehkanani, Z. D ; Fotowat ahmady, A ; Sobhi, J ; Farrell, R ; Sharif University of Technology
    John Wiley and Sons Ltd  2018
    In this paper, a reconfigurable receiver front-end for the frequency range of 800 MHz to 2.5 GHz is presented. The radio frequency front-end is realized in wideband form with reconfigurable baseband filter. The proposed front-end targets the GSM, WLAN, WCDMA, and GPS standards residing in the aimed frequency range. The necessary specifications for each individual standard have been revisited and recalculated. The interaction of the different standards and their interoperability has been thoroughly investigated and extra specifications derived for the multistandard receiver. The multistandard receiver has been designed, layouted, and simulated in RFCMOS 0.18-μm process. Copyright © 2018 John... 

    Improving the efficiency and directivity of THz photoconductive antennas by using a defective photonic crystal substrate

    , Article Optics Communications ; Volume 412 , April , 2018 , Pages 74-79 ; 00304018 (ISSN) Rahmati, E ; Ahmadi Boroujeni, M ; Sharif University of Technology
    Elsevier B.V  2018
    One of the shortcomings of photoconductive (PC) antennas in terahertz (THz) generation is low effective radiated power in the desirable direction. In this paper, we propose a defective photonic crystal (DPC) substrate consisting of a customized 2D array of air holes drilled into a solid substrate in order to improve the radiation characteristics of THz PC antennas. The effect of the proposed structure on the performance of a conventional THz PC antenna has been examined from several aspects including radiation efficiency, directivity, and field distribution. By comparing the radiation performance of the THz antenna on the proposed DPC substrate to that of the conventional solid substrate, it... 

    Investigations on equivalent circuit models of high frequency transformers

    , Article Proceedings of 2018 IEEE International Conference on Power Electronics, Drives and Energy Systems, PEDES 2018 ; Volume 2018-January , April , 2018 , Pages 475-480 ; 9781538646977 (ISBN) Hadizade, A ; Naghibi Nasab, J ; Aghaei, M ; Kaboli, S ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2018
    High frequency transformer is an important component in lots of modern power electronic circuits. In order to analyze the behavior of these transformers, equivalent circuit models containing parasitic elements have been proposed. But most of them are complicated and not appropriate to use in processes in which high speed analysis is crucial. In this paper, a second-order simplified model for high frequency transformers is obtained. Besides, the frequency ranges in which the proposed model has enough precision, are calculated and examined. To validate the simplified circuit model, some simulations are carried out. During the simulation, the effects of transformer equivalent circuit parameters... 

    Invariant wideband spectrum sensing under unknown variances

    , Article IEEE Transactions on Wireless Communications ; Volume 8, Issue 5 , 2009 , Pages 2182-2186 ; 15361276 (ISSN) Taherpour, A ; Gazor, S ; Nasiri Kenari, M ; Sharif University of Technology
    In this paper, we divide a wide frequency range into multiple subbands and in each subband detect whether in a primary user (PU) is active or not. We assume that PU signal at each subband and the additive noise are white zeromean independent Gaussian random processes with unknown variances. We also assume that at least a minimum given number of subbands is vacant of PU signal and propose an invariant Generalized Likelihood Ratio (GLR) detector. The concept of the grouping of subbands allows faster spectrum sensing of a subset of subbands which may be occupied by a specific PU. Also, we evaluate trade-offs involved in the proposed algorithms by simulation. © 2009 IEEE