نشریه الکترومغناطیس کاربردی
سال دهم شماره 2 (پیاپی 25، پاییز و زمستان 1401)

In this paper, a two-dimensional computational model is implemented to study all the necessary phenomena in a simple one-stage plane depositor by considering the interactions between the electrostatic field, the flow field, the charge of the particles and their turbulent motions. In the first step of this paper, while presenting the connections between electrostatic fields, particle dynamics and fluid dynamics, the mathematical model of the corona field, air flow and particle motion is explained. In the following, the electrical conditions (electric field and space charge) and the induced flux pattern are analyzed by the interaction of ion wind and the main gas flux in the studied model. Also, while examining the path of movement and accumulation of particles, their sediment distribution in the channel is investigated and the partial efficiency of particles with different diameters is calculated. In the following, the effect of electrohydrodynamic flux on the efficiency of the equipment is investigated. Finally, considering the normal logarithmic distribution for particles at the input of the sediment channel, the effect of different concentrations of particles at the input on the overall efficiency of the equipment is analyzed. This model is simulated in COMSOL software.

Surge arresters are used to protection of high voltage equipment and power transmission lines. Due to the presence or absence of shielding wire in transmission lines, surge arresters play an important role in reducing overvoltages. In this paper, the performance of an external gap arrester is investigated by considering different values of ground resistance and also the effect of soil ionization. The effect of lightning strike parameters such as rise time and tail time on overvoltage, insulator failure and energy absorbed in surge arrester for 63 kV transmission line without shielding wire has been simulated and studied in EMTP-ATP software. Considering the effect of the ground system, the use of external gap line arresters has provided better results compared to conventional arresters. Also, the surge arresters in the transmission line with shielding wire have a different operation from the transmission line without it. The results show that the surge arrester with an external gap compared to the surge arrester without gap has a better protective performance in absorbing energy and reducing overvoltage in this type of transmission line.

Metamaterial is defined as an artificial, macroscopic, and effectively homogeneous structure (with an average unit cell size much smaller than the guide wavelength). In the electromagnetic literature, the response of a system to an electric or magnetic field is largely determined by the characteristics of the materials in question. Two examples of these microscopic properties are the electric permittivity and magnetic permeability coefficients, both of which are positive in ordinary materials. By arranging an array of metal wires, a negative electric permittivity can be obtained, and by arranging an array of periodic split ring resonator structures, a negative magnetic permeability coefficient can be obtained. To model metamaterial structures, integral equations of electric field or magnetic field are used, which can be studied based on the numerical method of moment. One of the advantages of this method is that it only segregates the source, although the required memory increases in proportion to the size of the geometry of the structure. To solve this problem, today, alternative methods such as fast multipole method (single level and multi-level) are used, which in addition to the source, the basic functions and observation points are also segmented. In this paper, using surface integral equations and multi-level fast multipole method, the diffraction and calculation of scattering fields of some metamaterial surfaces are investigated and the importance of this method compared to the direct moment method is greatly reduced in the computation time, approximately 75%.

The standard methods for determining the efficiency of electric motors have been divided into two distinct categories; direct and indirect methods. Usually, it is difficult to prepare all necessary facilities and requirements for measuring the efficiency of in-service electric motors. Meanwhile, some online efficiency estimation methods have been developed for three-phase induction motors that can be used in necessity. In these methods, the output power of the three-phase induction motor is estimated by measuring electrical signals of the motor including current, voltage, active power, and power factor. Three-phase induction motor's in-service efficiency estimation methods are divided into four categories including slip method, current method, equivalent circuit method, and air gap torque method. The two latter mentioned methods have enough accuracy in comparison with the standard methods. In this article, previous literature on online and in-service efficiency estimation methods of three-phase induction motors, based on the equivalent circuit method and the air gap torque method are reviewed.

In the vast majority of previous research on electromagnetic rail launchers, either the two-dimensional analysis have been performed by finite element simulation, or in the case of three-dimensional study, armature and projectile motion have not been considered simultaneously. Due to the importance of the subject and the need to carefully study the behavior of this type of electromagnetic launchers, in this paper, simulations and analysis are performed in a completely three-dimensional manner, taking into account the armature motion. In this paper, two solid armature electromagnetic rail launchers, which have different geometry and dimensions, are simulated and analyzed in a completely three-dimensional manner, taking into account the armature motion, and compared in terms of different physical quantities. The main quantities in electromagnetic rail launchers include electric current density distribution, magnetic flux density distribution, inductance gradient, force and pressure on armature and rails, muzzle velocity and heat distribution, which are also changed by changing the geometry of the armature. In simulations, the powerful COMSOL Multiphysics software is utilized, which has the ability to solve the problems involved with several different physical phenomena, using the finite element analysis (FEM) method. Finally, according to the results of the simulations, the necessary analysis and comparisons have been made and the relative superiority of each of the structures under study in terms of the above quantities is presented.

In this paper, in order to improve the cogging torque in the radial flux magnetic gear with integer gear ratio, the axial pole skew technique has been used. This design reduces cogging torque by shaping the distribution of the magnetic field in the air gap of inner rotor in the axial and radial directions. In order to compare the proposed method, the optimal design of radial shaping in inner high speed rotor is also investigated. The introduced methods have been optimized using genetic algorithm in order to obtain the maximum torque density and the minimum cogging torque. The results are compared using 3-D finite element method and the superiority of the axial shaping method is shown in it.

Flux Reversal Machine (FRM) integrates the features of permanent magnet synchronous machines and switch reluctance machines due to the presence of permanent magnets in the stator tooth and the robust structure of the rotor. In this paper, a model of a 250-watt flux reversal machine with 12 stator slots and 17 rotor teeth is designed. Using the Taguchi optimization method with the help of Minitab, the flux reversal machine is designed to achieve minimum torque ripple and maximum output torque. The most important achievement of this paper is optimization with precise planning of the Taguchi method to determine the optimal combination of the desired parameters as well as acceptable compliance of the predicted results with the simulation results of Altair Flux.

The Vernier PM machine is known as a machine with high torque and low speed, which has several advantages such as higher torque density, lower PM material volume, lower gear torque, improved performance and simpler and more durable structure compared to other structures based on the magnet is permanent. These machines are a good option for use in electric vehicles. One of the proposed structures that is suitable for this purpose is the structure of the Dual-Stator Consequent-Pole Vernier PM machine, which has high torque density, optimal functional characteristics and lower magnet consumption. But for the complete design of this structure, mechanical studies including thermal and vibration studies must be done on the designed electromagnetic structure. This is important because of the different geometry of conventional radial flux machines, unbalanced magnetic forces, and mechanical and thermal constraints. In this paper, the design of heat transfer system and mechanical structure of DS-CP-VPM machine has been done and thermal and vibration studies have been performed. Design variables were selected based on sensitivity analysis using the finite element method. Several design limitations in geometric dimensions, current density and magnetic flux density in different areas and mechanical forces have been considered. The results are confirmed for a 10 kW car with a torque of 2 KN for the application of an electric vehicle using the three-dimensional finite element method. In this paper, the thermal-mechanical analysis of the engine is performed and the simulation results in Comsol software are evaluated.

Free electron laser technology is one of the most suitable options to achieve high power, coherent radiation in the range of short wavelengths, especially XUV and X. One of the most important challenges in construction of short-wavelength free electron lasers is the large dimension of the system. Therefore a significant part of free electron laser researches is concentrated on length reduction and radiation enhancement of the system. In this paper, the performance of free electron lasers in the range of XUV or soft X is investigated and some techniques for minimizing and radiation enhancement of the system are presented. For this purpose, methods such as using higher harmonics of the radiation field and pre-bunched injecting electron beam into the wiggler are proposed. To compensate for the decrease in the radiation power of the third harmonic, the wiggler tapering method was used to amplify the radiation field. Based on three-dimensional simulations performed using the MEDUSA code, it was observed that wiggler tapering can increase radiation power significantly. It was also found that using a pre-bunched electron beam can amplify saturation power and accelerate the growth process of the radiation field and thus reduce the saturation length of the free electron laser. Therefore, tapering of the wiggler field along with the beam pre-bunching method can play a very important role in length reduction and amplification of the radiation field of short-wavelength free electron laser.

Sensors are one of the most vulnerable electronic devices to high-power electromagnetic waves such as (HPEM), (UWB), and (EMP). To achieve such effects, a model of the effect of electromagnetic interference has been proposed. The susceptibility of such components to waves by finite element software (COMSOL MULTYPHYSIC) is simulated and vulnerability has been investigated. The results show the destruction of electronic components in the sensor during attacks. When the frequency of the pulse carrier is similar to the operating frequency of the target, it will be much higher. Parameters such as the angle of radiation or the proximity of the elements used in the sensor can also increase or decrease the degradability of the target. In this paper, the factors affecting the vulnerability of components during the emission of high-powered electromagnetic waves will be investigated and finally, the degree of damage will be shown.

In this paper,considering the effect of a strong uniformly axial magnetic field on the plasma dielectric tensor, electromagnetic fields and other results in a waveguide with a metal wall with a cross-section in the shape of a Piet Hein curve containing cold and strongly magnetized plasma is investigated using an appropriate approximation. First, by introducing the Pitt Hein waveguide, the electromagnetic wave equation in this type of waveguide is presented , using a suitable approximation and by separating the variables, as two separate differential equations. The electric and magnetic fields as well as the dispersion relations for the TM and TE modes are then calculated in a Piet Hein waveguide with a metal wall containing strongly magnetized cold plasma, and the dispersion relations and resulting fields are plotted., Next, the motion of an injected electron into this waveguide and the effect of a strong uniformly axial magnetic field on the electron energy is investigated. The electron motion and energy equations are written in the Pitt Hein plasma waveguide in the presence of a strong uniform axial magnetic field and are solved using fourth-order Runge Kutta method for TM and TE modes. The motion path and kinetic energy of the electrons injected into the waveguide have been graphically investigated for both modes.

In this research, the effect of adsorbent layer on the hydrogen gas sensing of tapered optical fiber sensors has been investigated. First, the taperd optical fiber is prepared by heating and pulling a single mode optical fiber. Then, by using magnetic sputtering method, two samples of palladium and palladium-copper layers were deposited on one-side of the surface of the fiber as an adsorbent layer. The results of X-ray energy dispersion spectroscopy analysis (EDX) showed that the ratio of palladium to copper in the sample area is 97. 53 to 2. 47%. Sensor operation tests for different percentages of hydrogen gas showed that the palladium-copper composite layer (Pd97. 53Cu2. 47) demonstrates lower sensitivity in comparison to the palladium layer Typically, the percentage change in output power in the presence of 3% hydrogen gas was 3. 38% for sensors with palladium-copper adsorbent layer and 16. 77% for sensors with palladium adsorbent layer. But anyway the response of the composite layer to different hydrogen precentages exposure is linear, in contrast to the palladium layer which shows a nonlinear behavior.