Search for: circuit-theory
0.007 seconds
Total 33 records

    A genetic-based tabu search algorithm for optimal DG allocation in distribution networks

    , Article Electric Power Components and Systems ; Volume 33, Issue 12 , 2005 , Pages 1351-1362 ; 15325008 (ISSN) Gandomkar, M ; Vakilian, M ; Ehsan, M ; Sharif University of Technology
    This article presents a new optimization algorithm based on integrating the use of genetic algorithms and tabu search methods to optimal allocation of dispersed generation resources in distribution networks. The proposed algorithm finds how much distribution losses can be reduced if dispersed generations are optimally allocated at the demand side of power system. A significant improvement of the proposed algorithm results, over that obtained by genetic algorithm, has been achieved. Numerical examples also showed the superiority of the proposed algorithm compared with the simple genetic algorithm. Copyright © Taylor & Francis Inc  

    Circuit model for extraordinary transmission through periodic array of subwavelength stepped slits

    , Article IEEE Transactions on Antennas and Propagation ; Volume 61, Issue 4 , 2013 , Pages 2019-2024 ; 0018926X (ISSN) Khavasi, A ; Edalatipour, M ; Mehrany, K ; Sharif University of Technology
    In this paper, two circuit models are proposed for analytical investigation of extraordinary transmission through periodic array of subwavelength stepped slits in a thick metallic plate. A cascade model is first developed and then a stub model is suggested for cases that the cascade model is not accurate. The parameters of the proposed circuits are given by closed-form expressions. Both symmetric and asymmetric stepped slits are considered  

    Circuit model for lamellar metallic gratings in the sub-wavelength regime

    , Article IEEE Journal of Quantum Electronics ; Volume 47, Issue 10 , Oct , 2011 , Pages 1330-1335 ; 00189197 (ISSN) Khavasi, A ; Mehrany, K ; Sharif University of Technology
    A circuit model is proposed for periodic 1-D array of metallic strips in the sub-wavelength regime. The parameters of the proposed circuit and their dependence on frequency are all explicitly given by closed form expressions. The necessity of using numerical simulation to extract model parameters is thus sidestepped. It is demonstrated that the proposed model is valid at different incident angles and for arbitrary surrounding mediums given that there is only one propagating diffracted order outside the grating and only one guided mode supported by the slits. Both major polarizations are studied in this paper  

    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  

    Motif structure and cooperation in real-world complex networks

    , Article Physica A: Statistical Mechanics and its Applications ; Volume 389, Issue 23 , 2010 , Pages 5521-5529 ; 03784371 (ISSN) Salehi, M ; Rabiee, H. R ; Jalili, M ; Sharif University of Technology
    Networks of dynamical nodes serve as generic models for real-world systems in many branches of science ranging from mathematics to physics, technology, sociology and biology. Collective behavior of agents interacting over complex networks is important in many applications. The cooperation between selfish individuals is one of the most interesting collective phenomena. In this paper we address the interplay between the motifs' cooperation properties and their abundance in a number of real-world networks including yeast proteinprotein interaction, human brain, protein structure, email communication, dolphins' social interaction, Zachary karate club and Net-science coauthorship networks. First,... 

    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... 

    Electrical equivalent circuit of multi-mode flexible beams with piezoelectric elements

    , Article Journal of Intelligent Material Systems and Structures ; Volume 19, Issue 5 , 2008 , Pages 621-627 ; 1045389X (ISSN) Saghafi, M ; Meghdari, A ; Sharif University of Technology
    Surface mounted piezoelectric sensors and actuators on elastic structures are often connected to electrical networks. The coupled equations of motion of the elastic structure with piezoelectric elements are already well known. However, due to complex behavior of some electrical elements in the electrical network, it is not an easy task to obtain the integrated equations of the whole system. A good remedy for this problem is to take advantage of an equivalent electrical circuit (EEC) representation of the mechanical part, leading the entire system to be represented as an electrical circuit. In this study, the authors propose a new method for constructing the EEC. This method is based upon the... 

    Frequency-dependent network equivalent for electromagnetic transient studies by vector fitting

    , Article IEEE Power Engineering Society Transmission and Distribution Conference, PES TD 2005/2006, Dallas, TX, 21 May 2006 through 24 May 2006 ; 2006 , Pages 166-171 ; 0780391942 (ISBN); 9780780391949 (ISBN) Porkar, B ; Vakilian, M ; Feuillet, R ; Sharif University of Technology
    The size and complexity of modern power systems necessitate the use of Frequency Dependent Network Equivalents (FDNE) for part of the system. In order to give realistic simulation the frequency response of the equivalent must mach that of the system it represents. In this paper a method for developing FDNE is presented and demonstrated by approximation its admittance matrix Y by rational function in the frequency domain based on vector fitting method. The developed FDNE is accurate and efficient. An example showing the accuracy and efficiency of the developed FDNE when used to reduce a radial network is presented. ©2006 IEEE  

    A 1.5V 150MS/s current-mode sample-and-hold circuit

    , Article 2005 European Conference on Circuit Theory and Design, Cork, 28 August 2005 through 2 September 2005 ; Volume 2 , 2005 , Pages 91-94 ; 0780390660 (ISBN); 9780780390669 (ISBN) Sedighi, B ; Rajaee, O ; Jahanian, A ; Bakhtiar, M. S ; Sharif University of Technology
    A high-speed current-mode sample-and-hold circuit is presented. This circuit allows for high sampling speed together with high linearity and precision. The sample-and-hold circuit has been designed and simulated in standard 0.18μm CMOS technology with 1.5V supply voltage. It is capable of operation with sampling frequency of 150MHz (300MHz using double sampling technique) for 12-bit accuracy using 3.7mW power  

    General solution of linear differential equations by using differential transfer matrix method

    , Article 2005 European Conference on Circuit Theory and Design, Cork, 28 August 2005 through 2 September 2005 ; Volume 3 , 2005 , Pages 113-116 ; 0780390660 (ISBN); 9780780390669 (ISBN) Eghlidi, M. H ; Mehrany, K ; Rashidian, B ; Sharif University of Technology
    A new analytical method for finding the general solution of the nth-order linear differential equation with variable coefficients is given based on generalizing the idea of differential transfer matrix method already proposed for solving the second order Helmholtz equation. Our generalization has two aspects. First, the given formulation copes with the nth-order linear differential equations, rather than the special case of second order wave equations. Second, the proposed approach is generalized in several different ways each yielding different types of differential transfer matrices with correspondingly different numerical accuracies. The presented methods can be applied to problems such... 

    Calculation and Distribution of Transmission Loss in Restructured Power Systems

    , M.Sc. Thesis Sharif University of Technology Ebrahimi Bojdani, Mohammad Reza (Author) ; Ehsan, Mehdi (Supervisor)
    The electric power industry is experiencing important changes brought about by the deregulation. Electric power generators and users engage in power transactions which take place over the transmission system and create losses. Transmission losses represent up to 1⎯5% of the total generation, and cost millions of dollars per year. Consequently, the problem of “who should pay for losses” arises and the satisfactory sharing of the transmission system utilization costs among all market participants has become a key issue. Unfortunately, losses are expressed as a nonlinear function of line flows, and it becomes almost impossible to calculate exactly the losses that are incurred by each generator,... 

    Circuit model for periodic array of slits with multiple propagating diffracted orders

    , Article IEEE Transactions on Antennas and Propagation ; Vol. 62, Issue 8 , August , 2014 , pp. 4041-4048 ; ISSN: 0018-926X Yarmoghaddam, E ; Shirmanesh, G. K ; Khavasi, A ; Mehrany, K ; Sharif University of Technology
    We propose an analytical circuit model for accurate analysis of one-dimensional periodic array of metallic strips. The proposed model is valid not only in subwavelength regime, but also for wavelengths shorter than the period of structure. The working frequency can reach the visible range and thus electromagnetic properties of periodic arrays of nano-slits can be analyzed by the proposed model. The proposed model remains valid for arbitrary incident angles even when nonspecular diffracted orders become propagating. Analytical expressions are derived explicitly in order to describe the parameters of the proposed circuit model. The circuit model is derived by assuming that only one guided mode... 

    Circuit model in design of THz transparent electrodes based on two-dimensional arrays of metallic square holes

    , Article IEEE Transactions on Terahertz Science and Technology ; Vol. 4, issue. 3 , April , 2014 , p. 383-390 Shirmanesh, G. K ; Yarmoghaddam, E ; Khavasi, A ; Mehrany, K ; Sharif University of Technology
    In this paper, we propose a circuit model for two-dimensional arrays of metallic square holes located on a homogeneous substrate, in order to propose a new scheme containing this type of metamaterials to obtain transparent electrodes with simultaneous terahertz transparency and low electrical resistance. The results of the introduced circuit model, which is a fully analytical model with explicit expressions, are in almost complete agreement with the full-wave simulations. Thanks to this analytical model, we can employ standard binomial matching transformer in order to minimize the reflected power from the structure at a desired frequency. Furthermore, taking advantage of this model, we... 

    Circuit model for mode extraction in lossy/lossless photonic crystal waveguides

    , Article Journal of the Optical Society of America B: Optical Physics ; Volume 29, Issue 1 , 2012 , Pages 170-177 ; 07403224 (ISSN) Habibi, N ; Khavasi, A ; Miri, M ; Mehrany, K ; Sharif University of Technology
    An approximate circuit model is proposed for mode extraction in two-dimensional photonic crystal waveguides. The dispersion equation governing the complex propagation constant of the photonic crystal waveguide is then related to the resonance condition in the proposed circuit model. In this fashion, a scalar complex transcendental equation is given for mode extraction. To avoid searching for the complex roots of the derived scalar dispersion equation, however, the real and imaginary parts of the sought-after propagation constant are extracted by using the physical resonance condition and its corresponding quality factor in the here-proposed circuit model, respectively. All the necessary... 

    A small signal circuit model of two mode InAs/GaAs quantum dot laser

    , Article IEICE Electronics Express ; Volume 8, Issue 4 , 2011 , Pages 245-251 ; 13492543 (ISSN) Horri, A ; Faez, R ; Hoseini, H. R ; Sharif University of Technology
    In this paper, for the first time, we present a small signal circuit model of quantum dot laser considering two photon modes, i.e., ground and first excited states lasing. By using the presented model, effect of temperature variations on modulation response of quantum dot laser is investigated. Simulation results of modulation response are in agreement with the numerical and experimental results reported by other researchers  

    Analytical circuit model for periodic arrays of graphene disks

    , Article IEEE Journal of Quantum Electronics ; Volume 51, Issue 9 , July , 2015 ; 00189197 (ISSN) Barzegar Parizi, S ; Rejaei, B ; Khavasi, A ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2015
    In this paper, an analytical circuit model is proposed for 2-D arrays of graphene disks. First, we derive an analytical expression for the surface current density on a single graphene disk in the subwavelength regime, induced by a normally incident plane wave. The solution is then extended to 2-D arrays of graphene disks using perturbation theory. Finally, by applying appropriate boundary conditions, an R - L - C equivalent circuit of the structure is obtained. It is shown that both a single graphene disk and periodic array of graphene disks have dual capacitive-inductive nature. The results of the proposed model are in excellent agreement with those obtained by full-wave simulations  

    Identifying critical components for reliability centred maintenance management of deregulated power systems

    , Article IET Generation, Transmission and Distribution ; Volume 9, Issue 9 , 2015 , Pages 828-837 ; 17518687 (ISSN) Ghorani, R ; Fotuhi Firuzabad, M ; Dehghanian, P ; Li, W ; Sharif University of Technology
    Competition in the electric power industry urges utilities to not only reduce the investment costs, but also to reasonably cut the operation and maintenance expenses as much as possible, while keeping both power quality and reliability requirements met. Reliability-centred maintenance (RCM) has been proven to be in response to this dilemma in power systems and has been yet successfully applied in various engineering contexts. This study introduces a novel approach, as of the first steps of RCM implementation in composite power generation and transmission systems, to identify the critical components for the main sake of a more focused maintenance management. Criticality evaluation is, here,... 

    Design of mid-infrared ultra-wideband metallic absorber based on circuit theory

    , Article Optics Communications ; Volume 381 , 2016 , Pages 309-313 ; 00304018 (ISSN) Arik, K ; Abdollahramezani, S ; Farajollahi, S ; Khavasi, A ; Rejaei, B ; Sharif University of Technology
    Elsevier B.V  2016
    An ultra-broadband absorber of light is proposed by using periodic array of ultra-thin metallic ribbons on top of a lossless quarter-wavelength dielectric spacer placed on a metallic reflector. We propose a fully analytical circuit model for the structure, and then the absorber is duly designed based on the impedance matching concept. As a result, normalized bandwidth of 99.5% is realized by the proposed absorbing structure in mid-infrared regime. Performing a numerical optimization algorithm, we could also reach to normalized bandwidth of 103%  

    Circuit model for plasmons on graphene with one-dimensional conductivity profile

    , Article IEEE Photonics Technology Letters ; Volume 28, Issue 3 , 2016 , Pages 355-358 ; 10411135 (ISSN) Farajollahi, S ; AbdollahRamezani, S ; Arik, K ; Rejae, B ; Khavasi, A ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc 
    The scattering of graphene surface plasmons normally incident on a line discontinuity in graphene surface conductivity is investigated. The effect of the length of the transition region on the reflection and transmission coefficients is studied. It is shown that the reflection coefficient is reduced by widening the transition region. Based on the results obtained, a transmission line model is derived for the graphene sheet in which the discontinuity is represented by a simple circuit. This model is next used to design graphene-based bandpass and bandstop filters with arbitrary bandwidth in the terahertz regime  

    Generalized vector model for the brushless doubly-fed machine with a nested-loop rotor

    , Article IEEE Transactions on Industrial Electronics ; Volume 58, Issue 6 , August , 2011 , Pages 2313-2321 ; 02780046 (ISSN) Barati, F ; Shao, S ; Abdi, E ; Oraee, H ; McMahon, R ; Sharif University of Technology
    This paper presents a generic vector model for the brushless doubly-fed machine (BDFM) with a nested-loop rotor. The vector model is presented for a generic p1/p2 pole-pair BDFM which may have any number of loops per nest. The vector transformations utilized in the derivation of the vector model are provided in general form such that the model can be represented in any appropriate reference frames according to the specific application of the model, such as BDFM analysis, simulations, or control system synthesis. The derived vector model benefits from the feature of reduced order in comparison with the coupled-circuit model, which is the most detailed model for the BDFM, while maintaining the...