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Two building blocks of microwave photonics filters in the presence of group delay ripple: A comparative survey
, Article Optical and Quantum Electronics ; Volume 44, Issue 8-9 , 2012 , Pages 403-414 ; 03068919 (ISSN) ; Akbari, M ; Sharif University of Technology
Springer
2012
Abstract
We have developed an analytic approach to investigate the effect of group delay ripple of the dispersive devices on the performance of two major building blocks of microwave- photonic filters. Firstly, performance of PM-based block in the presence of an arbitrary group delay ripple (GDR) is analyzed and compared with the ripple-free case to reveal the destructive effects of added group delay ripple. In the next step, we repeat the proposed approach for the AM-based one; again, the performance is compared with the ripple-free case. Two distortion metrics are also introduced to quantify this distortion. Comparison of the performance of two building blocks in the presence of group delay ripple...
Methane molecule over the defected and rippled graphene sheet
, Article Solid State Communications ; Volume 152, Issue 15 , August , 2012 , Pages 1493-1496 ; 00381098 (ISSN) ; Neek Amal, M ; Sharif University of Technology
Elsevier
2012
Abstract
Adsorption of a methane molecule (CH 4) onto a defected and rippled graphene sheet is studied using ab initio and molecular mechanics calculations. The optimal adsorption position and orientation of this molecule on the graphene surface (motivated by the recent realization of graphene sensors to detect individual gas molecules) is determined and the adsorption energies are calculated. In light of the density of states, we used the SIESTA code. It is found that (i) classical force field yields adsorption energy comparable with experimental result and ab initio calculation; (ii) the periodic nature of the van der Waals potential energy stored between methane and perfect sheet is altered due to...
A perturbation method for analysis of TDM-pumped fiber raman amplifier
, Article Optical Fiber Technology ; Volume 15, Issue 4 , 2009 , Pages 353-362 ; 10685200 (ISSN) ; Farhadi, M ; Farman, F ; Sharif University of Technology
2009
Abstract
We propose a perturbation method for time division multiplexed (TDM) pumping fiber Raman amplifier (FRA). The method is based on the solution of Raman partial differential equations (PDEs) by a closed integral form. Taking the signals and pumps power as the interim solution and updating their values in an iterative process, Raman gain and pump/signal evolution can be calculated in any order of accuracy. In the first order of perturbation, some analytical formulas for the FRA dynamic control are obtained. Analytical formulas are employed for gain ripple minimization and also the gain clamping problem under channel reconfiguration. © 2009 Elsevier Inc. All rights reserved
Detection of High Frequency Oscillations in EEG Recordings
, M.Sc. Thesis Sharif University of Technology ; Shamsollahi, Mohammad Bagher (Supervisor)
Abstract
EEG Signal Processing has really important role in study of nerves system and nervous diseases. In most applications, signals occur in the frequency band ranging below 100 Hz are considered. In this study, the higher frequency components of the signal, especially in patients with epilepsy, reported which they are called high frequency oscillations (HFOs). Some sources considered that HFOs are up to 1000 Hz and some other considered up to 2500 Hz. In study of HFOs, the high frequencies between 100 and 200 Hz that are called ripple and seen in normal mode are separated from the faster frequencies from 200 to 500 Hz and these components can accurately help to detect epileptic foci generator (to...
Dynamic Modeling and Torsional Vibration Analysis of Crankshafts Equipped with DMF & CPVA
, M.Sc. Thesis Sharif University of Technology ; Sayyadi, Hassan (Supervisor)
Abstract
Torque variations caused by intermittent combustion and inertia effects of reciprocating components, exert significant torsional excitation on crankshaft of internal combustion engines. These excitation induces considerable torsional vibration on crankshafts. Therefore, modeling and analysis of crankshaft torsional vibration and absorber systems, especially in automobiles engine that crankshaft tolerate high amplitude excitations coupled with heavy inertia effects has high importance. In this study, ability of centrifugal pendulum vibration absorber and dual mass flywheel which used in rotating machinery for vibration reduction, will be examined. At first, cranktrain will be torsionaly...
Analysis and Improvement of Output Voltage Ripple in High Voltage DC Power Supply
, M.Sc. Thesis Sharif University of Technology ; Kaboli, Shahryar (Supervisor)
Abstract
The TWT is highly sensitive to the ripple amplitude of its power supply output voltage. If the amplitude of the output voltage's ripple exceeds a certain limit, the amplitude of the undesired harmonics in the power spectrum of the TWT is greatly increased. Increasing the amplitude of undesired harmonics in the TWT output power spectrum reduces the accuracy and performance of the TWT. Therefore, for optimum TWT performance, a low-ripple power supply is essential. Typically, a low-frequency rectifier or high-frequency switching structure is used to build a high-voltage DC power supply. In this thesis, the different structures of high voltage DC power supplies are studied. Next, by focusing on...
Reliability Improvement of the High Voltage Power Supply Based on Interleaved Inverters
, M.Sc. Thesis Sharif University of Technology ; Kaboli, Shahriyar (Supervisor)
Abstract
In some high voltage applications it is necessary for high voltage power supply (HVPS) to operate over a wide load and gain range. For instance a HVPS may be used to supply various microwave tubes. Our goal in this thesis is to design a HVPS which can provide a DC voltage between 0-15 KV and 0-5 KW. In convetional approaches, operating over wide load and gain range necessitates the switching frequency or duty cycle to swing over a wide range. This approach may disturb soft switching, consequently switching loss will increase. The control process will be more complex too. the wide swing range of switching frequency means that the HVPS needs to operate with low switching frequency too....
Optimization of the New Structure of the Reluctance Motor to Increase the Efficiency and Power-Density by Experimental Methods
, M.Sc. Thesis Sharif University of Technology ; Sayyaadi, Hassan (Supervisor)
Abstract
Permanent magnets play an essential role in the structure of the electric motor, but due to limited resources, many efforts have been made to meet the need for them. One of the most important types of non-permanent electric motors is reluctance motors. Despite their antiquity in design, torque ripples have led to the limited use of reluctance motors, but advances in science have made it possible to control these ripples.As a result of the major advantages such as low manufacturing costs, high efficiency, and uncomplicated structure, these motors have been the subject of many researches. One way to eliminate the problem of torque ripples is to increase the number of teeth, but in the common...
Analysis of Output Voltage Power Spectrum of High Voltage Power Supply
, M.Sc. Thesis Sharif University of Technology ; Kaboli, Shahriyar (Supervisor)
Abstract
Some microwave tubes can function as a narrowband power amplifier and their output power spectrum is an indicator of their amplification and efficiency. One of the factors affecting its power spectrum is the noise and ripple of its HVDC power supply. To reduce the negative effects of power supply, first there should be an exact measurement of ripple and noise in the output of the HVDC power supply. Destructive factors which affect voltage ripple measurement in the case of high DC voltage are follows as conductive interference, radiative interference, intrinsic noise of electrical elements, and nonideal frequency response of voltage divider. After identifying and suppressing the mentioned...
Direct torque control of brushless doubly-fed induction machines using fuzzy logic
, Article Proceedings of the International Conference on Power Electronics and Drive Systems, 5 December 2011 through 8 December 2011 ; December , 2011 , Pages 619-624 ; 9781612849997 (ISBN) ; Khayyat, A. A ; Sharif University of Technology
2011
Abstract
In this research, a Fuzzy Logic Direct Torque Control (FLDTC) based on stator flux-oriented and machine's relation and equations with voltage and current of both stators have been introduced. Initially, paper focuses on BDFM concept and development of it. The synchronous mode operation of BDFM will be studied, and then by introducing the d-q coordination, the dynamic equation of BDFM will be represents. Furthermore, this paper devotes a new predictive FLDTC in d-q coordination through a short review of some definitions in Fuzzy. In this method a novel expanded rule bases by twelve stator sectors represented. This algorithm is careless to the priority of flux and torque, and it is easily...
The group delay ripple effects on the performance of phase-modulator based microwave-photonic filter
, Article 2011 18th International Conference on Telecommunications, ICT 2011, 8 May 2011 through 11 May 2011, Ayia Napa ; 2011 , Pages 162-166 ; 9781457700248 (ISBN) ; Akbari, M ; Sharif University of Technology
2011
Abstract
We have developed an analytic approach to investigate the effect of group delay ripple on the performance of phase-modulated microwave photonic filter. Two cases with and without ripple are analyzed to clarify the ripple's effects on the performance of microwave-photonic filter. Comparison of our proposed analytical approach with simulated OptiSystem® results shows a good agreement
Detection of fast ripples using Hidden Markov Model
, Article 2014 21st Iranian Conference on Biomedical Engineering, ICBME 2014, 26 November 2014 through 28 November 2014 ; November , 2014 , Pages 348-352 ; 9781479974177 (ISBN) ; Montazeri, N ; Shamsollahi, M. B ; Kachenoura, A ; Wendung, F ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2014
Abstract
Studies show that High frequency oscillations (HFOs) can be used as a reliable biomarker of epileptogenic zone, thus many algorithms have been proposed to detect HFOs. Among the wide variety of HFOs, fast ripples (FRs) are important transient oscillations occurring in the frequency band ranging from 250 Hz to 600 Hz. The automatic detection of FRs can be degenerated by the presence of some 'pulse-like' events (commonly, the component of interictal epileptic spikes) associated with an increase of the signal energy in the high frequency bands, exactly as in the case of real FRs. The goal of this study is to propose a new method for automatic detection of fast ripples by using Hidden Markov...
Direct torque control of induction motor by active learning method
, Article PEDSTC 2010 - 1st Power Electronics and Drive Systems and Technologies Conference, 17 February 2010 through 18 February 2010, Tehran ; 2010 , Pages 267-272 ; 9781424459728 (ISBN) ; Akhbari, M ; Mokhtari, H ; Sharif University of Technology
2010
Abstract
This paper presents a high performance direct torque control (DTC) theme for the induction motor (IM). To solve those problems associated with conventional DTC, such as flux and torque ripple, variable switching frequency, inaccuracy in motor model and other parts of system. The Active Learning Method (ALM) is implemented on the DTC. In the Active Learning Method for information modeling, a method known as Ink Drop Spread (IDS) is used. The simulation results of DTC system based on ALM and the comparison of motor performance under the proposed control system with respect to those obtained under conventional DTC confirms its effectiveness and accuracy
Effect of direct coupling of microrings on the gain bandwidth of cascade microring Raman amplifier
, Article Optics Communications ; Volume 283, Issue 14 , Jan , 2010 , Pages 2939-2946 ; 00304018 (ISSN) ; Bazouband, F ; Nickfarjam, V ; Sharif University of Technology
2010
Abstract
A combination of coupled microrings that are coupled to a bus waveguide is proposed as a wide-band microring Raman amplifier. This structure is called one channel coupled microrings (OCCM) Raman amplifier. It is shown analytically that the number of poles in the OCCM transfer function is greater than the square of microrings number (N). The gain bandwidth and gain ripple of the proposed amplifier are increased and decreased, respectively due to increasing the number of poles and zeros in the transfer function. An iterative matrix method is introduced to solve Raman equations in the amplifier with arbitrary number of microrings and Genetic algorithm is employed to maximize the gain flatness
The effect of rippled graphene sheet roughness on the adhesive characteristics of a collagen-graphene system
, Article International Journal of Adhesion and Adhesives ; Volume 64 , 2016 , Pages 9-14 ; 01437496 (ISSN) ; Shamloo, A ; Sharif University of Technology
Elsevier Ltd
Abstract
A great amount of effort has been made in order to reach a more precise understanding of the adhesion phenomenon that happens as a vital component of several biological systems. Therefore, a firm understanding of the important factors that influence this phenomenon is of special importance in triggering the adhesive characteristics of different biological, bio-inspired and synthetic materials in fields such as tissue engineering. In this study the adhesive characteristics of a multi-material system consisting of the frequently used synthetic material, graphene, in the form of armchair-configuration sheets, and an important biological filament which is type 1 Collagen consisting of 3 alpha...
An isolated high power small-size interleaved full-bridge PFC rectifier for 400 volt telecom energy distribution systems
, Article 9th Annual International Power Electronics, Drive Systems, and Technologies Conference, PEDSTC 2018 ; Volume 2018-January , April , 2018 , Pages 186-192 ; 9781538646977 (ISBN) ; Tahami, F ; Sharir University of Technology
Institute of Electrical and Electronics Engineers Inc
2018
Abstract
In new 400 volt energy distribution systems for telecommunication sites and data centers power density is an influential factor which is commonly desired to be provided such that the systems occupy a small space. On top of that in 400 volt energy distribution systems galvanic isolation is investigated to be inevitable. In this paper a new method is presented that makes it possible to interleave the topology of an isolated low-cost low-size rectifier in which the DC link capacitor of power factor correction stage and DC-DC stage inductor are eliminated and as result it is shown that all the benefits of interleaving such as low current ripple and higher power density are combined with the...
Gain ripple minimization in the wide-band SCISSOR raman amplifier
, Article Optics Communications ; Volume 282, Issue 8 , 2009 , Pages 1648-1653 ; 00304018 (ISSN) ; Bazouband, F ; Sharif University of Technology
2009
Abstract
A side coupled integrated spaced sequence (SCISSOR) of Silicon or Chalcogenide glass microrings of different diameter are considered as a wide-band Raman amplifier. Because the two-photon absorption (TPA) losses in Chalcogenide glass are less than that of Silicon, it is shown that Chalcogenide microrings are suitable for wide-band Raman amplifier in the telecommunication bandwidth (1.5 μm). The Lagrange unknown multiplier method is employed to minimize the gain ripple of the amplifier versus the pump and system parameters. Crown Copyright © 2008
An Extremely low ripple high voltage power supply for pulsed current applications
, Article IEEE Transactions on Power Electronics ; Volume 35, Issue 8 , 2020 , Pages 7991-8001 ; Mohsenzade, S ; Hadizade, A ; Kaboli, S ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2020
Abstract
This article describes the development of an 18 kV, 30 kW power supply for a pulsed current load with the maximum current of 20 A and a di/dt equal to 100 A/μs. The achieved output ripple is less than 0.01%. In such a high level of precision, the most important issues are considerable difference between the instantaneous and average output powers, as well as insufficient reaction speed of the converter to the fast load change. Very low level of the voltage feedback and its sensitivity to the noise. The first issue necessitates a notable overdesign of the converter switches if the output voltage precision is dedicated to the converter. The second issue raises the problems relevant to...
A distortion-free phase-locked loop system for FACTS and power electronic controllers
, Article Electric Power Systems Research ; Volume 77, Issue 8 , 2007 , Pages 1095-1100 ; 03787796 (ISSN) ; Sharif University of Technology
2007
Abstract
This paper presents a single-phase phase-locked loop (PLL) system which is primarily free from the double-frequency ripples from which the conventional PLL system suffers. The proposed PLL is then extended to reject the harmonic components from the input signal and to estimate the phase-angle and frequency of the distorted input signal with no error. Three units of the proposed PLL can be used in three-phase power systems, such as FACTS and HVDC converters, to estimate the phase-angles of the individual phases with no double-frequency ripples and without sensitivity to the presence of harmonics and inter-harmonics. This makes the proposed PLL unique and desirable for applications which...
Development of New Wind Turbine Scheme and Pure DC Wind Farm based on Excitation Controlled Synchronous Generator
, Ph.D. Dissertation Sharif University of Technology ; Parniani, Mostafa (Supervisor)
Abstract
In this thesis, a new wind turbine scheme based on Electrically-Excited Synchronous Generator (EESG) and diode-bridge rectifier is proposed and developed. This new scheme is mainly based on the idea of generator excitation current employment as a means of wind turbine control. That is why the new scheme is called Excitation Controlled Synchronous Generator (ECSG) wind turbine. The most important aspects of the proposed ECSG wind turbine scheme are cost-effectiveness, simplicity and higher reliability, as well as higher efficiency. Considerable cost reduction for the converter unit of ECSG wind turbine is so important since costly converter has been one of the main challenges of the...