نشریه الکترومغناطیس کاربردی
سال نهم شماره 1 (پیاپی 22، بهار و تابستان 1400)

One of the multiplexing methods used in optical telecommunication systems that increases the data transmission rate is Wavelength Division Multiplexing (WDM). In this technology, the information produced by several separate transmitters can be sent simultaneously in the optical fiber and then the information is separated in the receiver. The use of WDM technology and erbium doped fiber amplifier (EDFA) has led to the dramatic growth of optical telecommunication systems, especially direct intensity modulation / detection (IM DD) systems. Today, in order to increase the data transfer rate, the use of coherent detection methods is considered.In this paper, the main purpose is to increase the data rate in optical telecommunication systems using WDM technology and increase the communication distance using EDFA. Therefore, we design and simulate an optical telecommunication system that in each WDM channel, the data transmission rate will be equal to 100 Gbps. To achieve the specified data rate, we also use Dual Polarization transmission, linear effect reduction (CD) and nonlinear (SPM) methods, coherent detection systems and signal processing methods. The simulation results in this paper showed that all the effective components considered in the design, achieved the desired quality factor with a communication distance of 80 km. Proper use of EDFA also improves the transmission link length by at least 100%.

The ceramic fracture in output RF1 window is one of the most important failure factors in high power vacuum tubes. Fast protection systems are used to protect the tube. These protection systems are activated with some measured variables such as the level of backward RF power. On the other hand, a fast protection system can be activated with noise. Therefore, a tradeoff must be done between the response time of the protection system and its sensitivity to the noise. There are many methods to determine the response time of the protection system. The level of allowable power loss in the tube failure process is one of the conventional figures of merit for protection response time determination. However, these methods are conservative and the resulted response time is usually less than the critical time which is necessary for protecting the tube. In this paper, an experimental investigation is presented about the relation between the response time of the tube protection system and the crack growth in the ceramic of RF window. It is shown that the twin growth in ceramic can be a reliable figure of merit for the response time calculation of the tube protection system.

In this paper, a dynamic model is provided to obtain the waveform of the unbalanced magnetic force in the wound rotor induction machines with static eccentricity. The provided dynamic model is based on the voltage state-space equations of the coupled circuits in the eccentric induction machine. In the model the slotting effect and saturation is neglected and the slot ampere turn is distributed on the slot opening. To avoid computation of the air gap flux density and evade of magnetic pressure integration in each time-step of Runge-Kutta computations and consequently reducing the computation time of dynamic simulations, a static function of the stator and rotor windings’ currents are proposed for computation of the unbalanced magnetic force. The parameter of the proposed function is obtained by analyzing the air gap field density by using winding function theory. Finally, the waveform of the unbalanced magnetic force of the eccentric induction machine is obtained and verified by time-stepping finite elemnt analysis.

Besides introducing the triple-speed coaxial magnetic gear, the paper studies the influence of the geometric structure on torque and tangential and radial flux density. As rectangular and trapezoidal structures are more welcomed in most projects thanks to their ease of use, the present paper also introduces triple-speed coaxial magnetic gears with rectangular and trapezoidal structures. Then these gears are compared with crescent-shaped magnetic gear using the finite element method. The comparison shows that rectangular magnetic gears are not much different from crescent-shaped gears in terms of the flux density on the edges and corners. However, flux density distribution is more desirable in the former as the air gap between the middle rotor and modulators is variable, and less oscillation is experienced considering tangent and radial flux density distributions. Nonetheless, the trapezoidal structure presents unsatisfactory performance in comparison to the crescent-shaped structure in terms of flux density distribution and torque. An experimental crescent-shaped magnetic gear was built. The obtained results prove the validity of the use of this structure in triple-speed coaxial magnetic gears and the high performance of it compared to other structures used in magnetic gears.

In this paper, approximate and exact equivalent circuits for grounding electrodes buried in horizontally two-layered soils are introduced. In the approximate one,  two-layer soil is approximated with equivalent resistivity and then the grounding electrode is modelled with RLC equivalent circuit, while in the exact one, the input impedance of the grounding electrode is first computed in the frequency domain via numerical solution of Maxwell’s equations. Then the input impedance is replaced with rational functions and finally the equivalent circuit in time domain is achieved. In order to extract the validity range of the approximate circuit in two-layer soils, transient analysis of overhead line terminated to arrester in the presence of two-layer soils is carried out where the grounding electrodes are modelled with approximate and exact circuits. The simulation results show that when the thickness of the first layer is less than 1 meter or greater than 40 meter, the approximate circuit yields acceptable results. In addition, sensitivity analysis is carried out on the thickness of the first layer with respect to the single-layer soil. The simulation results show that when the thickness is greater than 40 meter, the two-layer and single-layer soils have the same behavior.

This paper presents a new structure in the magnetic gearbox field, which can bring better performances rather than the conventional one. This work aims to describe a developed magnetic gear with a novelty in its physical structure which cause gearbox can experience a new magnetic field distribution. Having experienced a further distribution in its magnets plan, the new model can reveal better performances rather than the original coaxial gearboxes. Although dimensions of the new coaxial gearbox get smaller than the ones in typical design, torque transfer and fluctuating rates have incredibly improved. Simulation results, based on the proposed models, are extracted from a time-stepping finite element analysis. ANSYS Maxwell software uses the Finite Element Method in its calculations and reports the results to validate the magnetic systems operations.

Superconducting microwave circuits are composed of components made from superconducting microstrip transmission lines (SMTLs). The spatial features of the superconductors provide the system operation at high speed and low noise floor. However, coupling the external electromagnetic field in these systems reduces or nullifies their performance. In this article a general solution for evaluating the electromagnetic behavior of SMTL in different incidence angles is proposed. The analysis is portrayed in the spectral domain. Using the proposed approach, the electromagnetic susceptibility (EMS) of the line is evaluated for oblique incidence. It is investigated for different film thicknesses. The study reveals that the line's susceptibility has the highest value at 80o. But, its value varies for different thicknesses. Different behavior of the induced current for different thicknesses is due to the difference in equivalent impedance. Moreover, due to increase in the equivalent reactance, the line's susceptibility is decreased as the film thickness is decreased.

In this paper, an ultra-wide-band Metamaterial Absorber with simple structure and optimum dimensions and thickness is proposed for X-band applications. This structure design with using three split circular rings and its dimensions optimized with HFSS. The unit cell of the proposed absorber has low dimensions and thickness (thickness 0.066λ_0 at 10 GHz central frequency). An array of 24 × 24 elements of the proposed metamaterial absorber with dimensions of  〖170×170 mm〗^2 was constructed and evaluated in practice. The structural parameters of resultant Metamaterial including permeability (μ) and permittivity (ε) are extracted by using Nicolson- Rose method. The results of simulation and practical measurement, show that, almost in total X-band rang (of 7.3 GHz to 11.5 GHz), the structure of the absorption bandwidth is 90%. Also, the studing of the results shows that, there is a good agreement between the acting measurement and simulation. The designed structure was also tested for the angles of perpendicular and obliquely incident electromagnetic wave, that, up to 45 degrees, absorption bandwidth did not change much.

In this paper, a new design of a wide band rectangular microstrip patch antenna in Ku-band using multilayered dielectric structure is presented for broadband RADAR and satellite applications. In this compact design, a conductor pin is used to excite the radiating patch. The parasitic patch is separated from the radiating one by air gap. The obtained 10-dB impedance bandwidth of the antenna is improved to more than 22%. The variations in the measured gain of the proposed antenna are less than 1 dB in the whole bandwidth. The simulation and fabrication results of the proposed antenna are in a good agreement.

The design of a dual mode ferrite phase shifter with linear polarization is investigated in this paper. Phase shifters are one of the most commonly used components in phased array radars. The main parts of this phase shifter are ferrite rod, yoke and polarizer. The main specifications of phase shifter are 10.1-10.7 GHz bandwith, less than 1 dB average loss and 360 degree phase shift. Due to the limitations of manufacturing in some parts, a parametric analysis has been performed on some specifications and the allowable amount of changes in these parameters such as yoke and ferrite rod contact length and the air gap between them, the length and radius curvature of polarizer has been reported.

Design and analysis of a magnetic gear (MG) needs to pricise calculation of flux density distribution along the MG. However applying the finite element methode is relatively accurate, it takes a long time in the preliminary design process in order to study the effective parameters. One of the new structures of MGs is consequent-pole mahgnetic gear (CPM) kind that saves the permanent magnet (PM). In this paper, the 2-dimensional (2D) modeling of a CPM using magnetic equivalent circuit (MEC) method is presented which determines the distribution of magnetic fields, fluxes, and torques of inner and outer rotors. To evaluate the performance of the proposed model, a CPM is analysed with two pole PM arc coefiecinet and flux density is extracted in different parts of CMG as well as its radial and tangential  component of tourqu. Furthermore, to confirm the proposed model results, the finite element analysis was performed by Ansoft / Maxwell software that verifies the MEC results.

The earth grid at high voltage substations should provide safety for people and normal equipment operation, therefore design calculations should be consideredaccurately. Step and touch voltages are among the items that affect people’s safety at high voltage substations. Grounding is suitable so that in addition to having low electrical resistance to the ground, it does not increase the step and touch voltages. Among the factors that laed to an increase in the electrical resistance of the earth’s grid is the tearing of the earth’s grid due to factors such as corrosion of conductors. In this article we provide a description of the appropriate design of high voltage substations grid to simulate the overhead substation grid and its effect on step and touch voltages in ComsulMultiphysics software based on the finit element method. After performing the simulation,it is noticed  that the stepand touch voltages in the two-and three-piece earth’s grid are much higher than the healthy earth’s grid and about 48 times comparing with the normal grid.