
حسن
آبروش
author
text
article
2007
per
For evaluating quality of electrical insulation, it is necessary to measure the property of insulators. Dielectric constant and loss tangent (tans) are two important parameters for determining the property of insulator. The measurement of above parameters is normally based on the time domain and frequencydomain, which is costly and time consuming.
In this study a multiplefrequency binary sequence signal was applied to the specimen, which is a periodic voltage that switches rapidly between two presets values. Since the applied voltage is periodic, therefore the results are obtained by using a numerical Fourier series analysis. The difficulties associated with Fourier transform are avoided. By applying the above method, capacitance (dielectric constant) and loss tangent is measured over a wide range of frequency.
University College of Engineering
دانشکده فنی
08031026
41
v.
7
no.
2007
https://jfe.ut.ac.ir/article_19002_59f26dca2bf6b11936006e41814ff8a1.pdf

حسین
افراخته
author
محمودرضا حقی
فام
author
text
article
2007
per
In this paper, effect of the islands number variation in restoration process is investigated and a graph based method for determination of optimum islands boundaries is presented. Also, the effect of number and location of blackstart units on the restoration process is evaluated. In optimization process, objective function is minimizing Energy Not Supplied (ENS) and constraints are voltage margins in buses, transmission lines capacities and generators loading limits. The ENS is evaluated based on generation capacity allocation to demand loads method. Genetic algorithm (GA) is the base of optimization and a suitable chromosome coding is developed to network modeling and applying to the algorithm. In order to assess the capabilities of proposed method, the IEEE118 bus network has been used as test system and the results of sectionalizing the test system to 2, 3, 4, 5, 6 and 7 islands and the optimum boundaries of each island have been given in case studies section.
University College of Engineering
دانشکده فنی
08031026
41
v.
7
no.
2007
https://jfe.ut.ac.ir/article_19003_b7a75405cacceeb9bc8941f32d251deb.pdf

فائقه
امیرزاده
author
محمود کمره
ای
author
غلامرضا داداش
زاده
author
text
article
2007
per
In this paper a novel method for computing the radiation pattern and also the input impedance of a planar rectangular microstrip antenna array with consideration of mutual coupling and mutual impedance is presented. Each two triangles with a common edge make an Edge element or RWG. Any such edge element is considered as an infinitesimal dipole. The electrical currents over each dipole can be calculated by solving an electric field integral equation (EFIE), using the method of moments. Using the resulting surface currents and considering the mutual coupling effect between the elements, the radiation pattern of the whole array is obtained employing a new method, which we call it “active element pattern based on RWG edge element”. Moreover, using the above mentioned model for the edge elements and also considering the mutual impedance between the elements, the input impedance of the array is now calculated.
University College of Engineering
دانشکده فنی
08031026
41
v.
7
no.
2007
https://jfe.ut.ac.ir/article_19004_081a448b8844960223cacc15ecb99c2c.pdf

نیما
ایزدی
author
امیر
سماک
author
شمس الدین
مهاجرزاده
author
text
article
2007
per
In this paper, we report vertical etching of polyethyleneterephtalate plastic substrates by means of a chemical solvent and in the presence of ultraviolet illumination. Since the PET substrate is not dissolved in solvent without a UV source, only the desired areas with proper opening for UV exposure are removed in a vertical fashion. The etch rate varies between 1 and 8 micrometer per minute, depending on the process conditions. Various structures such as microgears and interdigital structures have been realized using this approach. Combining this method with electroplating, the fabrication of micromotors, microvalves and optical devices would be possible.
University College of Engineering
دانشکده فنی
08031026
41
v.
7
no.
2007
https://jfe.ut.ac.ir/article_19005_700b75cfa304caed0960c4952edeae48.pdf

حمیدرضا
بخشی
author
آذر
محمودزاده
author
text
article
2007
per
One of the important issues in many of array systems such as Radar, Sonar, Mobile, and satellite telecommunications is the estimation of DOA of narrowband received signal. CRB is very important in evaluation of parameter estimation. CRB is the lower bound estimation error variance for any unbiased estimation. In this paper, the array antenna with equal distance arrays is extended in two separated subarrays. At first we study the lower bound of estimation error variance for DirectionofArrival in array antennas using CRB method. Then, with extending the above method, the estimation error variance for DirectionofArrival in array antennas with two separated subarrays is computed. It is observed that if the size of array increases, the estimation accuracy also increases. But the cost of array and complication of the system also increase. Therefore, we suggest using array antennas with separated subarrays. Furthermore, when signal to noise ratio in the communications system is low, by using of array antennas with two separated subarrays, the DirectionofArrival is estimated with high accuracy.
Simulation results show that as the distance between the two subarrays and the distance between the antennas increase, the estimation error variance decreases. It should be noted that the distance between antennas should not be more than wavelength of received signal. This causes the ambiguity in estimation and grows up the sidelobes
University College of Engineering
دانشکده فنی
08031026
41
v.
7
no.
2007
https://jfe.ut.ac.ir/article_19006_a29a3928bceafd9d92985f21ecbcf76e.pdf

محمد
ترکمندی
author
محمد تقی حمیدی
بهشتی
author
text
article
2007
per
University College of Engineering
دانشکده فنی
08031026
41
v.
7
no.
2007
https://jfe.ut.ac.ir/article_19007_89e9dd1f6d8cac972521c41358e9d868.pdf

سعید
جلیلی
author
علی اکبر
صدری
author
text
article
2007
per
Nowadays, the automated text classification has witnessed special importance due to the increasing availability of documents in digital form and ensuing need to organize them. Although this problem is in the Information Retrieval (IR) field, the dominant approach is based on machine learning techniques. Approaches based on classifier committees have shown a better performance than the others. In this research, in addition to study text classification techniques and classification committees, two ideas in this field are proposed.
The first idea, is proposed based on Bagging committees. According to this idea, first, a training set by one of clustering techniques automatically is divided into several clusters based on class similarity (or dissimilarity). So for documents of every cluster, a classifier is trained and put in the committee as a member. In this approach the members of committee are created by the same technique. In our experiments for this idea, Naïve Bayesian, Rocchio and SVM learning techniques are used.
In the second idea, the creation of two layered committee is discussed. Based on this idea, one committee can be created that its members are itself a committee. Members of subcommittees are creating based on the first idea. This idea is based on the fact that if Naïve Bayesian committee acts better than Naïve Bayesian classifier and so, a committee out of these committees will improve the performance of classification.
Evaluation of the first idea showed that the improvement in performance based on precision and recall in Naïve Bayesian committee is exceeded the other committees (respectively 12 and 5.1 percent). Evaluation of the second idea showed that the improvement in performance in the second type of committee (based on the second idea) is more than that in the first type of committee (based on the first idea). Most improvement of performance in the second type of committee is referred to the Rocchio’s committee (based on precision and recall 3.8 and 18.8 percent, respectively).
University College of Engineering
دانشکده فنی
08031026
41
v.
7
no.
2007
https://jfe.ut.ac.ir/article_19008_5a5b5ed685c648224df07d56293550d1.pdf

ابراهیم رحیم
پور
author
وحید
رشتچی
author
اسماعیل مشهدی
رضاپور
author
text
article
2007
per
Regarding the fact that a detailed model of a transformer can be obtained by help of an internal physical structure of transformer; this model can be used to study internal phenomena of transformer in different conditions. In order to simulate transformer behavior in frequency domain by a detailed model, it is necessary to calculate the parameters of model as precisely as possible.
In this paper a detailed model based on self and mutual inductances is used for simulation of a high voltage winding of a 1.2 MVA distribution transformer. After calculating the parameters of the detailed model by analytical formulas, it has been seen that the calculated parameters cannot simulate transformer exactly, because of approximation in formulas and tolerance of transformer manufacturing. This study presents a new method based on genetic algorithm that can be used for determination of the detailed model parameters for more precise simulating of transformer transfer function.
University College of Engineering
دانشکده فنی
08031026
41
v.
7
no.
2007
https://jfe.ut.ac.ir/article_19009_595fb256d9162c68b7a6897e1b1eae4f.pdf

حبیب اله
زلفخانی
author
جلیل راشد
محصل
author
فرخ حجت
کاشانی
author
text
article
2007
per
Modern microwave and millimeter wave phased array antennas are attractive because of their ability to steer wave beams in space without physically moving the antenna element. A typical phased array antenna may have several thousand elements fed by a phase shifter for every antenna, which can steer the resulting array beam to different directions. Their low loss, low cost and lightweight phase shifters are important for the design of phased array antennas. The ferrite phase shifters have low insertion loss and can handle significantly higher powers, but they are complex in nature and have a high fabrication cost. While semiconductor phase shifters using PIN diodes or FET’s are less expensive and smaller in size than ferrites, their application is limited because of high insertion losses. Recently, others types of phase shifters using MEMS technology have been investigated to overcome the above limitations.
This paper presents analysis and design of distributed MEMS phase shifters for Kaband communication systems. The phase shift can be obtained by changing MEMS bridge capacitors located periodically over the transmission line. Simulation results of phase shifters with various structural parameters are analyzed to develop the optimized designs. It is observed that the distributed microelectromechanical transmissionline (DMTL) phase shifter can be accurately modeled using a combination of fullwave electromagnetic and microwave circuit analysis. The fullwave electromagnetic simulation of the unit cell is done by finite element using Ansoft High Frequency Structure Simulator (HFSS). After the full wave analysis is performed, Sparameters are extracted in the frequency range going from 26 to 40 GHz for different widths and heights of the MEMS bridge. Sparameter presentation of phase shifters is very important in computer aided design (CAD). Finally, the Sparameters are combined to obtain the overall phase shifter performance over Kaband. This phase shifter offers the potential for building a low loss device for a variety of phased arrays and radar. The average insertion loss and return loss and the phase errors of our phase shifter are compared with the reported MEMS phase shifters at various references.
The overall performance of nbit phase shifter is obtained, using Sparameters and microwave circuit theory. Using phase shifts versus numbers of cells, it is shown that the nbit phase shifter can be obtained with a suitable combination of onebit phase shifters with 11.25, 22.5, 45, 90 and 180 degrees. Insertion losses, return losses, and phase shifts ware obtained in 32states at the frequency range 2640 GHz. Average insertion loss –1.68 dB, return loss –11.94 dB, and phase errors of 2.33 was obtained in 33 GHz for 4bit phase shifter. The results are in good agreement in comparison with the reported MEMS phase shifters.
University College of Engineering
دانشکده فنی
08031026
41
v.
7
no.
2007
https://jfe.ut.ac.ir/article_19010_989c3e1ee91decb565eac9ca13cdba3d.pdf

سید محمد
عظیمی
author
سعید
افشارنیا
author
text
article
2007
per
University College of Engineering
دانشکده فنی
08031026
41
v.
7
no.
2007
https://jfe.ut.ac.ir/article_19011_019933eeb90ac43fda32c29bc6f7c52a.pdf

حسن
منصف
author
طاهر
قمیان
author
text
article
2007
per
This paper introduces Artificial Neural Network (ANN) method for measuring voltage in the Optical Voltage Transducer (OVT) using one or more electric field sensors. In order to obtain an accurate voltage measurement with minimum number of sensors, first the locations of sensors are specified by quadrature method. Then the electric field intensity at these locations is provided to ANN for the calculation of applied voltages. Less number of sensors with no displacement required to obtain high accuracy is the most important advantage of this method. The numerical simulations demonstrate the effectiveness of this technique.
University College of Engineering
دانشکده فنی
08031026
41
v.
7
no.
2007
https://jfe.ut.ac.ir/article_19012_91c00573763b5b9de468388829a7cffa.pdf

حسین هارون
آبادی
author
محمودرضا حقی
فام
author
محمود فتوحی
فیروزآباد
author
text
article
2007
per
Deregulation policy has caused some changes in the concepts of power system reliability assessment. This paper deals with generation reliability evaluation in perfect competition power market using market economic concepts and its dynamic. Also, because of power markets and generators’ forced outages stochastic behavior, Monte Carlo Simulation (MCS) is used in this research. Generation reliability merely focuses on interaction between generation complex and load, and it’s supposed that transmission and distribution systems are reliable. Therefore, this paper using perfect competition market subjects and demandoffer curves interaction, deals with generation reliability evaluation. The proposed method is assessed on IEEEReliability Test System (IEEERTS), and reliability indices are evaluated with various parameters.
University College of Engineering
دانشکده فنی
08031026
41
v.
7
no.
2007
https://jfe.ut.ac.ir/article_19013_c591a64d2f7b64b1408eee13d15ed726.pdf