Amirkabir International Journal of Electrical & Electronics Engineering
Volume:55 Issue: 1, Winter-Spring 2023

In this paper, a procedure is proposed to design a wideband transmitarray upon a specified frequency band. In this way, the phase control parameter of a unit cell is adjusted in a suggested range, ensuring linear phase change and low transmission loss over the band. The unit cell is designed for a range of phase control parameters (e.g., slot length in a CSRR), in which a 360° phase variation is provided. Part of this range is applied for the central elements of TA, in which the maximum overlapped passband (for different values of phase control parameter) around the desired frequency is to be achieved. In this way, a scenario for the phase specification of the array elements would be obtained. This range is specially applied for the central elements of the array, which are in exposure to feed peak power. As a proof of this concept, a 14×14 element transmitarray is designed and fabricated based on a back-to[1]back square Complementary Split-Ring Resonator (CSRR). Measurement results indicate maximum gain, 1-dB bandwidth, and aperture efficiency of 24.6 dB, 18.4%, and 53% respectively, at the center frequency of 11.5GHz. At the end of the paper, a comparison between the proposed TA and the previous ones is provided.

Image inpainting is the process of filling in damaged or missing regions in an image by using information from known regions or known pixels of the image. One of the most important techniques for inpainting is convolution-based methods, in which a kernel is convolved with the damaged image iteratively. Convolution based algorithms are very quick, but they don’t have good results in structures and textural regions and result in blurring. The kernel size in the convolution-based algorithm is a critical parameter. The large size results in edge blurring, and if the kernel size is small, the information may not be sufficient for reconstruction. In this paper, a novel convolution-based algorithm is proposed that uses known gradient of the pixels to construct a convolution mask. In this algorithm, the kernel size is controlled by the gradient of the image in the known regions. The algorithm computes the weighted sum of the known pixels in a neighborhood around a damaged pixel and replaces the value in the place of that damaged pixel. The proposed algorithm is fast and results in good edges and smooth regions reconstruction. It is an iterative algorithm and its implementation is very simple. Experimental results show the effectiveness of our algorithm.

A Reflectarray Antenna is designed to operate at X-band as a Local Multipoint Distribution Service (LMDS) base station antenna. It is a center-fed single layer reflectarray consisting of 23×27 elements. The unit cell of the reflectarray has linear polarization with more than 400° linear phase shift and its geometrical parameters have been optimized to achieve wide bandwidth and low cross polarization (XP) level for the reflectarray. An iterative design procedure, that is valid for obtaining any arbitrary pattern, has been implemented to achieve the specified radiation pattern over a desired frequency range. The method has been successfully applied to a LMDS base station antenna, characterized by a sectorial cosecant squared beam in the frequency range of 9.3 GHz - 11.5 GHz. The simulation results are in a good agreement with the design requirements. The antenna has cosecant squared pattern over the bandwidth of 21%, XP level better than -30 dB, and SLL less than -20 dB in both elevation and azimuth planes. The total size of the 23×27-element array is 246×289 mm2 , and its 1dB gain bandwidth is wider than 19%. The proposed antenna performs significantly better than similar structures and has all the features and standards required for LMDS base station antenna

Double-circuit power systems are one of the main types of modern transmission lines due to their reliability. Fault location in these transmission lines has always been a potential problem due to the mutual coupling between lines. Accordingly, this paper presents a novel objective function for the fault location using synchronous post-fault measurements of currents and voltages captured by distance protective relays. Moreover, a fast and accurate modern metaheuristic optimization algorithm for this cost function is proposed, which are key parameters to estimate the fault location methods based on optimization algorithms. In this regard, first, the input data (current and voltage signals) were refined using some auxiliary functions such as Fast Fourier transformation (FFT), Decaying Dc Elimination (DDE), and frequency tracking algorithm to accurately extract the fundamental component of the voltage and current signals. Afterwards, the proposed fault location based on the proposed metaheuristic optimization algorithm estimates the fault location using these input signals. The main advantage of the presented algorithm is the parallel estimation processing to improve the convergence speed and the accuracy of the objective function of the fault location, and was applied to various fault types and various operating conditions to validate the performance of the proposed approach. In addition, the performance of the proposed method was compared with different fault location methods. The simulation was implemented in the PSCAD and MATLAB® software. The simulation results show that the novel proposed approach outperforms other fault locations in estimating the fault location.

Today, there are various sources of information in different fields that users can refer to. Generally, the presence of a question in users’ minds leads to reference to these sources of information. Users can search for the answer by entering a few keywords in search engines. They can also ask their questions in more detail in the Community Question Answering (CQA) networks so that experts can give a more comprehensive answer to their questions. To get the proper answer, it is necessary to address all the required details in the question. The questions posted in these networks can be divided into clear and unclear. In this study, an attempt has been made to extract unique features from the questions through various machine learning approaches, which can be used to classify questions. To extract these features, the word vector of each question was created, and then using unsupervised algorithms, the questions with similar word vectors were placed in the same group. Afterwards, repetitive concepts were extracted from each group, and their repetition rate in each question makes its feature vector. Finally, the questions were classified based on the extracted feature vector, using ensemble classification models. The achievement of this study is an efficient classification model along with efficient high-resolution feature extraction for classifying clear and unclear questions in CQA networks. Compared to other baselines and transformer[1]based models on different datasets, the proposed method makes high accuracy results.

Input-Parallel Output-Parallel DC-DC converters are convenient for high voltage and high current applications. One important goal of this type connection is to power-share and reduce circulating current between the converters. Therefore, control methods for power-sharing between converters should be used when the parameters mismatch. In this paper, a configuration comprising two DC-DC common grounded Z-source converters with Input-Parallel Output-Parallel connections is presented, which common grounded Z-source converter have advantages over similar converters. This study proposes two control strategies: (1) a decentralized inverse-droop control, (2) a general control strategy. Inverse-droop control is a simple method and does not need any communication between parallel converters. In the general control strategy, each converter is self-contained, and no external controller is required for achieving input/ Output Current Sharing, and a few wires are needed to create the entire system. The simulation results of an Input-Parallel Output-Parallel system comprising two common grounded Z-source converters are evaluated for investigating effectiveness of general control and inverse-droop control. It reported performance of the general control method to be better than the decentralized inverse-droop control method, which enhances the stability and dynamic characteristics of the system. The validity of the two control strategies has been studied through MATLAB simulation and the results were satisfactory.

Exposure protective clothing has been suggested as a protection against RF and microwave electromagnetic fields, especially for pregnant women. These clothings are usually made of metal-woven fabrics. In this article, we use computer simulation methods with a homogeneous human model and plane wave exposure at different polarizations and wave incidence angles over a wide range of frequencies to inspect if a typical anti-exposure clothing model might fail to reduce the fields inside the body under certain exposure conditions and/or at some frequencies. Indeed, as far as our model and computational study can represent actual conditions, it is found that for waves incident along the body axis (as arises e.g. in the sleeping status against a cell-phone tower) the clothing might not only fail to reduce the penetration of EM fields, but can rather increase the electric field intensity in certain body areas, including the abdominal parts which were intended to be protected during pregnancy. We conclude that more physics-aware designs should be employed for such clothing.

There are numbers of technical limitations that must to be satisfied for the operation of the power systems, and these limitations are related to the power flow of the power system, thus the solar panels cannot inject any unlimited amount of power into the power system. Therefore, the maximum injection power of solar panels is limited to the specific value. This issue is also true for the reactive power produced or consumed by SVCs and solar panels, so the maximum injected power of photovoltaic panels must be obtained in such a way that the technical limitations of the power system are maintained. In the current research, a 33 bus radial distribution network has been considered and the goal is to maximize the injection power of photovoltaic panels, minimize the network power losses, by reconfiguring in this type of the network and establishing effective coordination between the control devices, including the output reactive power of photovoltaic panels and the fire angle of the SVC and graph of the power system. The bus voltage should be within the allowed range, and the cost of purchasing electricity from the upstream network should be minimized. The results of the simulation on the 33 bus radial network confirm the validity of the above claims.

A major challenge in the development of an assistive exoskeleton robot is to design appropriate control algorithms. These algorithms should be trajectory-independent and require a minimum number of sensors to work in any intended motion and to be easily implementable. As a simple assistive strategy with all promising features, Delayed Output Feedback Control (DOFC) is shown to be effective in assisting the wearers in different types of motion. In this method, the assistive torques are defined in proportion to delayed feedback from the angle difference between the two legs. The authors have recently suggested an intelligent version of DOFC, in which a Deep Q-Network (DQN) was used to adjust the feedback delay according to the speed of the motion. Simulation studies were used to investigate the idea. By conducting some real-world experiments, the present paper extends the results to practical conditions. The provided results clearly verify that if the time delay is adjusted according to the walking speed, the DOFC method can effectively help the users in their motions of any speed. The results also indicated that a fixed or an inappropriate value of the delay may result in resistance against the user motion.

In this paper, the effects of ionization and dispersion of a lossy soil on the Grounding Potential Rise (GPR) of buried multiple vertical rods under lightning return strokes are simultaneously studied. In all studies, an efficient modeling method, called improved Multiconductor Transmission Line, is adopted. In the case of a single rod, it is shown that the simultaneous occurrence of soil ionization and dispersion causes further reduction in the value of GPR as compared to the case where each phenomenon takes place separately. The amount of reduction is further accentuated when treating highly resistive soils and fast-fronted lightning currents. In the case of multiple rods, however, the value of GPR in both ionized and dispersed soil lies between those of the only-ionized and only-dispersive soils. Besides, the sensitivity analysis of the non-homogeneity effect in ionized and dispersive soils provides a comprehensive platform to study the soil dependence of the GPR of buried rods in a multi[1]layer soil. Finally, closed-form expressions are proposed that can accurately predict the value of GPR for both single and multiple rods buried in a dispersive and ionized lossy soil when subjected to a lightning current waveform.

A distributed control strategy is proposed to enhance voltage regulation and reactive power sharing in Low Voltage (LV) distribution networks with high penetration of Photovoltaic (PV) systems. This paper investigates the disadvantages of the available methods that their aims are modifying the voltage profile levels of buses and managing the reactive power of PV inverters. Next, through the proposed method, PV systems reduce the deviation of voltage profile by absorbing or injecting reactive power. This paper eliminates the disadvantages of the available control method by the combination of distributed and local control approaches. Indeed, a local droop characteristic determines the reactive power ratio of the worst bus voltage deviation at a critical bus. Afterwards, the distributed control coordinates all PV systems to operate according to the PV system that locates at the critical bus. In addition, the proposed technique prevents PV systems from active power curtailment and manages reactive power sharing among PVs based on their reactive power ratings. A radial LV distribution system with seven PV systems is presented to analyze the proposed procedure. Simulation consequences are demonstrated to confirm the effectiveness of the control method for decreasing voltage deviation and precise reactive power sharing in the distribution network with PV systems.

New applications such as 3D graphics, 3D displays, and image-based modeling have made stereo vision an active research area in recent years. In dense disparity map estimation, which is a basic problem in stereo vision, using two left and right images taken from a scene from two different positions, the disparity of each pixel of the reference image is determined (meaning determining each pixel with how displacement is appeared in the other image). Based on the disparity value, the depth of each pixel in scene is simply determined. For dense disparity map estimation, local stereo matching methods are simpler and faster than global methods, and therefore suitable for real time applications. In these methods, defining proper window which aggregate intensity pattern as well as keeping disparity consistency in all the window area, is an important challenge. To overcome this challenge, the idea of directional multiple window has been proposed in the previous researches. On the other hand, local binary patterns have considerable success in pattern recognition applications, while computationally simple. Therefore, the idea of using local binary pattern in a directional multiple window arrangement is proposed for dense stereo matching in this paper. Experimental results on standard stereo images show the better performance of the proposed method with respect to other proposed binary descriptors