Omid Shekoofa
@emu.edu.tr
Mechanical Engineering
Eastern Mediterranean University
I hold the position of assistant professor within the Department of Mechanical Engineering at Eastern Mediterranean University.
EDUCATION
I received my Ph.D. degree from the Department of Electronic Engineering of Tsinghua University.
RESEARCH, TEACHING, or OTHER INTERESTS
Electrical and Electronic Engineering, Renewable Energy, Sustainability and the Environment, Aerospace Engineering, Mechanical Engineering
Scopus Publications
Scholar Citations
Scholar h-index
Scholar i10-index
Scopus Publications
Somayeh Taran, Nasibe Alipour, Kourosh Rokni, S. Hadi Hosseini, Omid Shekoofa, and Hossein Safari
Elsevier BV
Daniyal Khosh Maram, Maryam Haghighi, Omid Shekoofa, Hamidreza Habibiyan, and Hassan Ghafoorifard
Elsevier BV
Farid Nazari, Mehdi Taherkhani, Majid Mokhtari, Hadi Aliakbarian, and Omid Shekoofa
Institution of Engineering and Technology (IET)
In this study, a multidisciplinary design procedure for sandwich radomes is presented. This methodology is composed of two parallel paths which are related to each other, one for electromagnetic behaviour and the other for its mechanical properties. The electromagnetic performance and mechanical properties are often mutually related resulting in a parameter selection compromise between them. The presented methodology is applied on an A type sandwich panel for C-band weather applications. It is composed of primary electromagnetic and mechanical designs, dielectric constant measurement, and electromagnetic and mechanical optimisations. Mechanical design of the sample panels according to survival wind loading of 220 km/h is done numerically and experimentally. Pressure distribution on the radome structure caused by the wind load is calculated numerically. The critical buckling load (120 N) is reported according to ASTM C364 edge wised compression standard test. A sample A-type sandwich panel with the respective thicknesses of 13.2 and 0.6 mm for its core and face sheets, respectively, is fabricated and tested. The dielectric constants of each are measured by using two methods and the results, which are in agreement in both methods, are ∼1.05 and 3.3, respectively. The insertion loss of the fabricated panel is lower than 0.2 dB over the entire desired band.
Omid Shekoofa, Jian Wang, Dejie Li, and Yi Luo
MDPI AG
Microcrystalline silicon, which is widely used in the microelectronics industry, is usually fabricated by chemical vapor deposition techniques. In recent years, magnetron sputtering has been considered as an alternative because it is a simpler, cheaper and more eco-friendly technique. The big drawback of this technique, however, is the need to recrystallize the as-deposited amorphous silicon, which can be done by metal-induced crystallization. Among the different suitable metals, copper has not been extensively investigated for this purpose. Furthermore, the applicability of the microcrystalline film prepared by this method has not been evaluated for photovoltaic device fabrication. Therefore, this paper reports the fabrication of p-type microcrystalline silicon thin film by magnetron sputtering and copper-induced crystallization techniques, and evaluates its appropriateness for solar cell fabrication. In the first step, 60 nm of silicon followed by 10 nm of copper were deposited on n-type silicon wafer and glass substrates, both by the magnetron sputtering technique. Then, the as-deposited samples were annealed at temperatures from 450 °C to 950 °C. The crystal properties of the resulting films were characterized by Raman and X-ray diffraction spectroscopies and optical and secondary emission microscopies, while their electrical characteristics were determined by Hall-effect, J-V curve and external quantum efficiency measurements. These characterizations confirmed the formation of a layer of microcrystalline silicon mostly in the <111> direction with a crystallization ratio of 93% and a largest grain size of 20 nm. The hole concentration and mobility of the fabricated p-type microcrystalline silicon layer were about 1017~1019 cm−3 and 8 cm2/V.s, respectively. By using the fabricated film as the emitter layer of a p-n junction solar cell, a good rectification ratio of 4100 and reverse saturation current density of 85 nA.cm−2 were measured under dark conditions. The highest photovoltaic conversion efficiency, i.e., 2.6%, with an open-circuit voltage of 440 mV and short-circuit current density of 16.7 mA/cm2, were measured under AM1.5G irradiance. These results indicate that microcrystalline silicon created by magnetron sputtering and copper-induced crystallization has considerable potential for photovoltaic device fabrication.
Daniyal Khosh Maram, Hamed Abnavi, Hamidreza Habibiyan, Hassan Ghafoorifard, and Omid Shekoofa
IEEE
An important tool for explaining the hysteretic behavior in movement of electronic and ionic charges is drift-diffusion model. Adding numerical methods to these models in realistic operation situations is challenging due to the fact that some parameters have extreme values. We present a time scale dimensionless model that considers charge carrier motion and ion migration in a perovskite solar cell. The proposed model provides high accuracy accompanied by the use of realistic parameters. In order to solve matrix and equations, tridiagonal matrix algorithm (TDMA) method is exploited. Electric potential, density of ion vacancy migration, hole and electron concentration characteristics are calculated and illustrated in transient time scale. Besides, the mentioned characteristics are illustrated with different feasible built-in potential. This approach gives insight into device physics, charge transport model, ion migration and hysteresis phenomena.
Jalaledin Tayebpour, Behzad Ahmadi, Mojtaba Fallahzadeh, Omid Shekoofa, and Abdorreza Torabi
Institute of Electrical and Electronics Engineers (IEEE)
A novel dual-pole dual-throw (DPDT) waveguide switch is proposed for high-power and low-loss applications. The proposed DPDT was designed based on the contactless properties of the gap waveguide technologies in the Ku frequency band. The DPDT was composed of two concentric contactless cylinders. Standard rectangular waveguide ports (WR 75) and waveguide paths are machined in the middle of these cylinders. The rotational movement of the inner cylinder is realized using two bearings in the top and bottom of the DPDT. The proposed structure is fabricated and the measured results are in good agreement with the simulated ones. The measured insertion loss and return loss for the aligned ports are better than 0.1 and 25 dB in the frequency band ranging from 11 to 13.5 GHz, respectively, and the measured isolation between two adjacent ports is better than 60 dB.
M.J. Esfandyari, M.R. Hairi Yazdi, V. Esfahanian, M. Masih-Tehrani, H. Nehzati, and O. Shekoofa
Elsevier BV
M.J. Esfandyari, V. Esfahanian, M.R. Hairi Yazdi, H. Nehzati, and O. Shekoofa
Elsevier BV
Daniyal Khosh Maram, Hamidreza Habibiyan, Hassan Ghafoorifard, and Omid Shekoofa
IEEE
In this paper, numerical simulation of a lead halide perovskite-based solar cell with ultrathin Cu2o (Copper oxide) as inorganic hole transporting material is investigated. The proposed thickness and properties of Cu2o layer must be precisely tuned in order to achieve the optimal cell characteristics. The influences of effective density of states, hole mobility of hole transporting layer, thickness of perovskite absorber and P-type Cu2o layer are considered in details. Improvements in efficiency are achieved by changing the Cu2o and absorber layer thickness. Based on the best possible optimization, power conversion efficiency exceeding 13% is obtained. Simulated values after optimization are described in detail, lead to have a better insight of design, referred to experimental works for achieving high-efficiency solar cells.
Omid Shekoofa, Jian Wang, Dejie Li, Yi Luo, Changzheng Sun, Zhibiao Hao, Yanjun Han, Bing Xiong, Lai Wang, and Hongtao Li
Elsevier BV
Omid Shekoofa and Jian Wang
IEEE
$P$-type micro-crystalline Silicon thin film was realized by magnetron sputtering and copper-induced crystallization for photovoltaic applications. Firstly, amorphous Silicon film was deposited by direct current magnetron sputtering from highly-doped single crystalline Si target. Then it was crystallized by copper-induced crystallization in nitrogen atmosphere with the annealing temperatures ranges from 450 to 950°C. The microcrystalline Silicon thin film was characterized by X-ray diffraction and Ramon spectrometry. Its grain size and crystallization ratio were approximately 20 nm and 93%, respectively. Finally, a PN junction solar cell was fabricated by creating the P-type microcrystalline Si thin film (as the $P$ region) on a highly-doped N-type Silicon wafer (as N region). The fabricated device showed the good rectification characteristics of a typical diode where under dark condition it represented the rectification ratio of 150 and reverse saturation current density of 9 μA.cm-2. The fabricated solar cell showed a significant photovoltaic effect under AM 1.5G illumination conditions. The highest photovoltaic conversion efficiency of 2.1%, with the open-circuit voltage of 416 mV and short-circuit current density of 13.3 mA/cm2, was measured from the sample fabricated by the optimal process.
Omid Shekoofa, Jian Wang, Dejie Li, Yi Luo, Changzheng Sun, Zhibiao Hao, Yanjun Han, Bing Xiong, Lai Wang, and Hongtao Li
Elsevier BV
Omid Shekoofa, Jian Wang, Yi Luo, De Jie Li, Changzheng Sun, Zhibiao Hao, Yanjun Han, Bing Xiong, Lai Wang, Lei Wang,et al.
IOP Publishing
Two different layer orders of p-Si/Al (as structure #1) and Al/p-Si (as structure #2) thin films were deposited on n-type mono-crystalline Silicon wafer and quartz glass by magnetron sputtering at 200 °C. The fabricated films were annealed at different temperatures for various durations. Then, they were analyzed by XRD, Raman and SEM methods. According to XRD results the largest grain size of both structures was smaller than 20 nm. The Raman spectra of the samples annealed at 1000 °C determined a crystallization ratio of 98% and 75% of structures #1 and #2 respectively. SEM images confirmed that the crystallization happened for structure #1 at lower temperatures than for structure #2. The impact of annealing on electrical and photovoltaic performance of the samples were studied after the fabrication of metal contact by sputtering of a few hundred nanometers of aluminium. The highest measured Voc were 360 and 402 mV, and the best Jsc were 2.2 and 0.12 mA/cm2, for structure #1 and #2 respectively.
Omid Shekoofa and Jian Wang
IEEE
This paper introduces a new model for gallium arsenide (GaAs) solar cells. GaAs technology plays an important role in the high efficiency solar cells industry. GaAs solar cells are fabricated in single-junction and multi-junction structures. The one that we study here is the mathematical model and electrical equivalent circuit of multi-junction solar cell, which is compared with the model of commercial single layer Silicon (Si) cells. Subsequently the modeling and simulation of a triple-junction cell is discussed and a new equivalent circuit model is proposed for triple-junction solar cells. We evaluate these models in various environmental conditions, cell specifications and physical dimensions. We consider three main factors: maximum power, short circuit current density and open circuit voltage of the solar cell. Taking into account the overall effect of temperature and solar irradiance, the proposed models are evaluated, and the resulted simulation data are presented. Results indicate that the proposed model accurately represent the cell operation in real conditions.
Jian Wang, Omid Shekoofa, Zhiqiang Yin, Jing Qi, Xijie Liu, and Wei Ke
Elsevier BV
Omid Shekoofa, Jian Wang, Jing Qi, Jian Zhang, and Zhiqiang Yin
Elsevier BV
Omid Shekoofa and Ehsan Kosari
IEEE
This paper focuses on evaluating three main design criteria including efficiency, reliability and cost for different topology schemes of Electrical Power Subsystem (EPS) of a satellite in Low Earth Orbit. Selecting an appropriate topology may increase the overall EPS efficiency and extend the lifetime of satellites. In this article, ten basic EPS topologies are studied, evaluated and compared. In order to choose a more efficient and more reliable EPS topology, along with cost considerations, the mentioned parameters would be calculated for each topology separately. In the next step, these topologies can be compared by defining an overall cost function composed of all three criteria.
Maryam Baghban and Omid Shekoofa
IEEE
This paper is a survey on major topics and basic phenomena of concern in electrostatic discharge occurrence on solar panels. Different mechanisms of electrical interactions between spacecraft solar array and space environment have been reviewed for this purpose. The role of various parameters in arc inception is investigated from the different points of view. The article provides a road map for developing new software tools through categorizing and summarizing what parameters are needed to be considered, and how they should applied.
Omid Shekoofa and Shahab Karbasian
IEEE
Choosing an appropriate topology is a key step in the process of electrical power subsystem design. This selection should be done based on the design requirements implied from higher level like mission, system and subsystem levels. In this study the essential criteria selecting a suitable topology are discussed. This paper starts with an overview on EPS design process with emphasizing on EPS architecture and topology selection. Two concepts of energy transfer, i.e. Direct Energy Transfer and Peak Power Tracker, are reviewed and compared in details. For each concept different methods of main bus voltage regulation, like unregulated bus, regulated bus, semi-regulated bus, quasi-regulated bus and hybrid bus are discussed. They have been evaluated by comparing their advantages, disadvantages, and their applications in different space missions. These comparisons are carried out based on essential criteria for EPS design such as efficiency, complexity, reliability, weight and cost.
Omid Shekoofa
IEEE
Solar arrays are the power source for the majority of space missions. They are the reason for many anomalies and failures in the electrical power subsystem, because they have to operate in a very harsh environmental condition. Undergoing to such sever conditions for generally long space mission life times is capable of degrading or damaging almost any parts of the solar arrays. Therefore it is quite necessary to do the qualification tests on the space solar cells and panels as much as complete and accurate as possible. Various standards have been developed by different space organizations in order to improve the level of quality of solar arrays and to assure the consumers about the reliability of these expensive products. In this paper some of the standards and procedures developed by ISO, AIAA, NASA and ECSS are discussed according to their methods and requirements.
Omid Shekoofa, Nader Pouryaie, Kaveh Sohrabzadeh, and Mohammad Rezvani
IEEE
This paper intends to report and describe a variety of activities such as modeling, simulation, design, implementation, test and analysis in order to design and develop EMUBAT, a battery emulator for space applications. The first step of EMUBAT development is battery modeling which is performed by using a typical equivalent circuit. The required parameters for battery modeling are extracted by means of electrical characteristics curves which are presented in battery datasheets or obtained from battery testing. Then, the orbit parameter modeling is investigated for LEO and GEO satellites. Battery thermal conditions due to its in-orbit operations are modeled in the next step. Finally, the hardware configuration and the software structure of EMUBAT are described. Besides, a battery test setup is presented, which is established to facilitate the process of obtaining the required data and parameters, for EMUBAT modeling and simulation. This test setup also makes it possible to have an easier and more precise verification of the emulator outputs.
Omid Shekoofa and Mohsen Taherbaneh
IEEE
This paper intends to review and analyze the approach of power source sizing, which is an important step in Electrical Power Subsystem (EPS) design, based on change in orbit parameters. There are two main objectives for doing this research: 1) understanding the impacts of the orbital parameters change and the mechanisms of their interactions with the EPS design and operation, 2) evaluation of the importance of their effects. To this end, a typical LEO micro-satellite has been considered in different orbits, to investigate the impacts of variation in the main orbit parameters e.g. altitude and inclination angle. Then the sizing, operation and performance of power sources have been evaluated via comparing the results of in-orbit simulations of EPS operation. In addition, some indirect impacts of the orbit parameters change are evaluated, by analysis and calculation of the interaction between EPS and other subsystems. The results support and show how the sizing and operation of solar array and battery are under the influence of orbit parameters change via certain factors, such as orbit period, duration and the fraction of eclipse/sunlit phases, received solar irradiance by solar panels, and received thermal fluxes from the Sun. According to the acquired results, any altitude increment leads to have better margins in power source sizing but there is an optimum value for inclination angle from this point of view.
Omid Shekoofa and Mohsen Taherbaneh
IEEE
This paper starts by describing a silicon solar panel model based on a comprehensive solar cell equivalent circuit. Then, as a case study, four similar modelled panels are considered in lateral sides of a satellite as its power source. Considering the panel model with different combinations of its equivalent circuit essential elements, the model operation is evaluated in a orbit attitude with some eclipse times. The variations in output characteristics of the panels due to changes in received solar irradiance and panels' temperature are calculated for each equivalent configuration. The values of maximum generated power and total generated energy during a satellite typical period are compared for different spin rates. Finally, the best topology for panel equivalent circuit is stated based on the compared results.