ORIGINAL_ARTICLE
EFFECTS OF FACET PHASES AND REFLECTIVITY ON THE INTERNAL OPTICAL FIELD IN QWS-DFB SEMICONDUCTOR LASERS
In this paper, the effects of reflected waves of the facets on the internal optical intensity of semiconductor DFB lasers are investigated. The uniformity of optical intensity along the cavity length is evaluated with flatness parameter. The dependence of this parameter on coupling coefficient, reflectivity and grating phase at the facets is also studied. This investigation shows that in some structures reflected waves of the facets cause optical intensity along the cavity length to have more uniformed distribution than a DFB laser with anti-reflective facets. It is also shown that flatness parameter is very sensitive to grating phase .Thus it is necessary for designing a DFB laser to consider the effects of reflected wave and grating phase at both ends of cavity in order to increase the stability of the laser against SHB (Spatial Hole Burning) effect. The effects of reflectivity and grating phase on longitudinal distribution of photon and carrier density above threshold are investigated, too.
http://mjee.modares.ac.ir/article_2035_e2384389e25b8c6f219587f81acd8ef9.pdf
2010-10-03T11:23:20
2017-11-25T11:23:20
1
12
QWS-DFB
Distributed feedback Lasers
Facet Reflectivity
Spatial Hole-Burning
Fateme
SHAHSHAHANI
f_shahshahani@alzahra.ac.ir
true
1
Amirkabir university of technology
Az.zahra university,tehran
Amirkabir university of technology
Az.zahra university,tehran
Amirkabir university of technology
Az.zahra university,tehran
AUTHOR
Vahid
AHMADI
av1385@gmail.com
true
2
Tarbiat Modarres University
Tarbiat Modarres University
Tarbiat Modarres University
LEAD_AUTHOR
Kavous
MIRABBASZADEH
true
3
Amirkabir university of technology
Amirkabir university of technology
Amirkabir university of technology
AUTHOR
ORIGINAL_ARTICLE
APPLICATION OF THE METHOD OF LEAST SQUARES FOR THE ANALYSIS AND DESIGN OF THE ELECTROMAGENTIC ENGINEERING PROBLEMS
In this paper, some applications of the Method of Least Squares (MLS) for the solution of various problems in electromagnetics engineering is briefly reviewed. Here, MLS is employed for the solution of various problems such as solution of equations, curve fitting to measured data, generalized Fourier coefficients, linear operator equations, inegro-differential equations, electrostatics and magnetostatics problems, boundary value problems (by the Least Square Boundary Residual Method LSBRM), design of impedance transformers and matching by step and tapered lines, optimum design of multihole directional couplers, coupled-line couplers, branch line couplers, ring couplers, analysis of wire antennas, antenna pattern synthesis, array synthesis and scattering. In this study, it becomes clear that MLS can be applied to devise effective numerical algorithms for the analysis and design of problems in the subject areas of radiation, scattering, antennas, microwaves, engineering mathematic, etc. Some papers and books published in the area of MLS applications for the analysis and design of problems in electromagnetics engineering are grouped and presented in references.
http://mjee.modares.ac.ir/article_2036_b5f1dea068caae7f4eefa0efd754dd8c.pdf
2010-10-03T11:23:20
2017-11-25T11:23:20
13
34
Method of Least Squares
Least Squares Boundary Residual Method
Numerical Methods in Electromagnetics
Error Function
Optimization
Minimization
Solution of Equations
Linear Equations
Integro-Differential Equations
Microwave Devices
Antennas
Arrays
Radiators
scattering
HOMAYOUN
OREYZI
h_oraizi@iust.ac.ir
true
1
Iran University of Science and Technology
Iran University of Science and Technology
Iran University of Science and Technology
AUTHOR
ORIGINAL_ARTICLE
DESIGN, OPTIMIZATION AND ANALYSIS OF HIGH POWER AMPLIFIER IN THE KA BAND
The graphical technique for nonlinear circuits was described that enable us to optimize circuits to obtain maximum output power, maximum efficiency or minimum intermodulation.
According to this method a high power amplifier in the Ka band was designed. Using a nonlinear model of the transistor, optimum slope for load-line was determined so that maximum power at the output was obtainable, then the output matching circuit was synthesized. Finally, the nonlinear network of the high power amplifier was analyzed by the harmonic balance method and the output load cycles were optimized by modification of the bias point or output matching network.
http://mjee.modares.ac.ir/article_2037_5b717c44aceec1efb6beb5fe19e3dd25.pdf
2010-10-03T11:23:20
2017-11-25T11:23:20
35
50
nonlinear model
PHEMT
graphical optimization
load cycle
Harmonic Balance
High Power Amplifier
Abdol Ali
ABDIPOUR
true
1
Amirkabir university of technology
Amirkabir university of technology
Amirkabir university of technology
AUTHOR
Mohammad
Hakkak
true
2
Tarbiat Modarres University
Tarbiat Modarres University
Tarbiat Modarres University
AUTHOR
Zahra
GHANIAN
true
3
Amirkabir university of technology
Amirkabir university of technology
Amirkabir university of technology
AUTHOR
ORIGINAL_ARTICLE
FIBER OPTIC NETWORKS PERFORMANCE EVALUATION
Performance of the fiber optic networks with different physical topologies such as point-to-point, bus, ring and star, with respect to requirements as bit rates, topology structure, bit. error rate (BER) and optical component characteristics including optical amplifiers, filters, sources and detectors, are analyzed and simulated.
For this purpose, maximum number of supportable nodes and throughput, crosstalk due to optical amplifiers and optical filters, reliability, physical limitations and fiber induced limitations such as dispersion and nonlinear effects (self phase modulation) are considered as performance evaluation criteria of different topologies.
Dispersion and nonlinearities are simulated with split-step Fourier method, sometimes referred to as beam-propagation method. The fiber length can be estimated by this method, with respect to above effects and maximum tolerable power penalties. Parameters such as maximum number of supportable nodes and crosstalk are evaluated using amount of degradation in BER of receiver, BER is calculated using Gaussian approximation. Reliability of networks is modeled on the bypassing of the failed station as recovery mechanism in ring and bus networks and reliable assumption for central node in star network. By the way physical limitations in each topology, regarding its structure, are derived as an economical criterion.
Results indicate that no topology can be preferred to others, however imposed limitations and requirements determine the optimum topology. Neglecting economical aspects, star topology is preferred from different points of view such as reliability, crosstalk and maximum number of supportable nodes. Results of above simulations can be used in calculating power penalties of different factors such as dispersion, crosstalk and nonlinearities. This penalties perform important role in estimating power budget of networks.
http://mjee.modares.ac.ir/article_2038_d5959b426ccd9403d270badaef788ebf.pdf
2010-10-03T11:23:20
2017-11-25T11:23:20
51
76
Self Phase Modulation
Traveling Wave Amplifier
Erbium Doped Fiber Amplifier
Crosstalk
Extinction Ratio
Fabry-Perot Filter
MAJID
MALAKOUTI
majid_malakuti@yahoo.com
true
1
Iran Telecommunication Research Center
Iran Telecommunication Research Center
Iran Telecommunication Research Center
LEAD_AUTHOR
Nasrollah
GRANPAYEH
true
2
K.N.Toosi university
K.N.Toosi university
K.N.Toosi university
AUTHOR
ORIGINAL_ARTICLE
ANALYSIS OF LARGE ELECTROMAGNETIC PULSE SIMULATORS USING THE ELECTRIC FIELD INTEGRAL EQUATION METHOD IN TIME DOMAIN
A time-domain approach is presented to calculate electromagnetic fields inside a large Electromagnetic Pulse (EMP) simulator. This type of EMP simulator is used for studying the effect of electromagnetic pulses on electrical apparatus in various structures such as vehicles, a reoplanes, etc. The simulator consists of three planar transmission lines. To solve the problem, we first model the metallic structure of the simulator as a grid of conducting wires. The numerical solution of the governing electric field integral equation is then obtained using the method of moments in time domain. To demonstrate the accuracy of the model, we consider a typical EMP simulator. The comparison of our results with those obtained experimentally in the literature validates the model introduced in this paper.
http://mjee.modares.ac.ir/article_2039_229540818da895150353747d1a2f1ea5.pdf
2010-10-03T11:23:20
2017-11-25T11:23:20
77
94
Electromagnetic pulse
Simulator
integral equation
Method of Moment
time domain
Jasem
JAMALI
true
1
Amirkabir university of technology
Amirkabir university of technology
Amirkabir university of technology
AUTHOR
Ramin
AGHAJAFARI
true
2
Atomic Energy Organization of Iran
Atomic Energy Organization of Iran
Atomic Energy Organization of Iran
AUTHOR
Ruzbeh
MOINI
moini@cic.aut.ac.ir
true
3
Amirkabir university of technology
Amirkabir university of technology
Amirkabir university of technology
AUTHOR
Seyed hossin
SADEGHI
true
4
Amirkabir university of technology
Amirkabir university of technology
Amirkabir university of technology
AUTHOR
ORIGINAL_ARTICLE
CORROSION OF CHROMATE CONVERSION COATINGS ON ALUMINUM ALLOYS IN ELECTRICAL AND ELECTRONIC EQUIPMENT
Chromate conversion coating is applied on aluminum 6061. The optimum conditions for chromate bath composition and immersion time are also obtained for standard requirements provision such as corrosion resistance in salt spray test, electrical resistance and coating quality. The applied coatings are electrochemically tested in sea and distilled water. According to Tafel and cyclic polarization curves, the protection mechanism are evaluated in said environments. This evaluation has shown the formation of passive film layer, contains chromate and alumina on the base. The proper behavior of corrosion and electrical conductivity is probably due to this mechanism.
http://mjee.modares.ac.ir/article_2040_0922dfb6e83d1999c8327594b34f513a.pdf
2010-10-03T11:23:20
2017-11-25T11:23:20
95
104
Corrosion
Chromate coating
Aluminum and Electrical and electronic equipment
Reza
SHOJA RAZAVI
shoja_r@yahoo.com
true
1
Malek Ashtar University of Technology
Malek Ashtar University of Technology
Malek Ashtar University of Technology
LEAD_AUTHOR
Taghi
SHAHRABI
true
2
Tarbiat Modares University
Tarbiat Modares University
Tarbiat Modares University
AUTHOR
Reza
MOZAFARINIA
true
3
Malek Ashtar University of Technology
Malek Ashtar University of Technology
Malek Ashtar University of Technology
AUTHOR
ORIGINAL_ARTICLE
A NEW METHOD FOR TOOL-PATH GENERATION AND ADAPTIVE INTERPOLATION OF A THREE-AXIS CNC MILLING MACHINE
In this paper we present a new method for tool-path generation and adaptive interpolation for a three-axis CNC milling machine. This method satisfied the force and / or the error conditions by using a variable-direction variable-feedrate strategy based on Maximum Feedrate Map. The proposed adaptive interpolator modifies the cutting path and the moving direction according to the actual instantaneous position error in real time. It also adaptively slows down the speed of the cutting tool if the position error exceeds a permissible threshold so as to decrease the error. As the cutting points on the spline at each cycle are not calculated beforehand, memory requirement for the interpolator drastically reduces. The significance of the proposed method on the reduction of the cutting error in the presence of disturbance is demonstrated via computer simulations.
http://mjee.modares.ac.ir/article_2041_97ae38c49bac08655a12af08ffd53682.pdf
2010-10-03T11:23:20
2017-11-25T11:23:20
105
114
Maximum Feedrate Map
Path planning
Adaptive Interpolation
Vahid
JOUHARI MAJD
majd@modares.ac.ir
true
1
Tarbiat Modarres University
Tarbiat Modarres University
Tarbiat Modarres University
LEAD_AUTHOR
Homan
HASANZADEGAN
true
2
Tarbiat Modarres University
Tarbiat Modarres University
Tarbiat Modarres University
AUTHOR
ORIGINAL_ARTICLE
AN IMPROVED MODEL BASED ON UTD FOR MULTIPLE DIFFRACTIONS BY BUILDINGS
In this paper, a new propagation model based on UTD for multiple diffraction paths in cellular mobile radio communications in urban environments is proposed. Moreover, the most rigorous novel UTD-based expressions for multiple diffractions by buildings and excess path losses are d - rived and analyzed. For this purpose, building rows are supposed to have rectangular cross-sections with the same heights and spacings. In addition, in this analysis actual electrical
roperties of buildings are regarded.
Previous studies have been concentrated on the simplified models that approximated building rows as absorbing half-screens or perfectly conducting half screens (knife-edges) or 90 degrees wedges. In this work, buildings are assumed flat-roofed parallel rows of dielectric blocks and their actual relative permittivity and conductivity are applied.
http://mjee.modares.ac.ir/article_2042_645058e54be62d0f5b909faa8a9161cb.pdf
2010-10-03T11:23:20
2017-11-25T11:23:20
116
126
Urban radio propagation
multiple building diffractions
excess path loss
uniform theory of diffraction
land mobile radio cellular systems
Reza
ARABLOUEI
a7923221@aut.ac.ir
true
1
Amirkabir university of technology
Amirkabir university of technology
Amirkabir university of technology
AUTHOR
Ayaz
GHORBANE
ghorbani@aut.ac.ir
true
2
Amirkabir University of Technology
Amirkabir University of Technology
Amirkabir University of Technology
AUTHOR
ORIGINAL_ARTICLE
A NOVEL ACTIVE POWER FILTER CONTROL METHODOLOGY
This paper presents a new control methodology for active power filters that provide an adaptive online harmonic estimation with partial and selective harmonic reduction schemes, which has been implemented within an integrated controller. The proposed approach is to provide partial and selective reduction of those individual harmonics which exceed the recommended levels as set by regulatory bodies reduces the rating of active power filters thus leading to cost savings. This approach contrasts with existing techniques in which the objective is to reduce all possible harmonic components to zero. Performance evaluation of the proposed technique for harmonic estimation for time-varying non-linear load is carried out when the simulation and experimental results show that the proposed control strategy provides a new alternative for harmonic reduction in power system.
http://mjee.modares.ac.ir/article_2043_9d6d3de282774456072fd45c692128a1.pdf
2010-10-03T11:23:20
2017-11-25T11:23:20
127
138
Harmonic estimation
Active power filter
Harmonic Reduction
ALI
YAZDIAN VARJANI
yazdian@modares.ac.ir
true
1
TARBIAT MODARRES UNIVERSITY
TARBIAT MODARRES UNIVERSITY
TARBIAT MODARRES UNIVERSITY
LEAD_AUTHOR
Jo
CHICHARO
true
2
Wollongog university,Australia
Wollongog university,Australia
Wollongog university,Australia
AUTHOR
Sarat
PERERA
true
3
Wollongog university,Australia
Wollongog university,Australia
Wollongog university,Australia
AUTHOR