نشریه الکترومغناطیس کاربردی
سال دهم شماره 1 (پیاپی 24، بهار و تابستان 1401)

Self- and mutual inductance are key parameters of the WPT system, and to optimize such systems or estimate its performance parameters such as received power, efficiency, and gain, the designer must calculate them correctly. Analytical calculation of self- and mutual inductance compared to the finite element simulation method speeds up the design process and reduces costs. The polarized DD pads are selected in this paper due to the simplicity of structure, high efficiency, and low sensitivity to misalignment conditions. DD pads are very popular in electric vehicle charging applications (dynamic and static). In this paper, analytical calculations of self and mutual inductance using Biot-Savart law for DD pads are presented. In some cases, the use of ferrite cores to improve the inductance and coupling coefficient of these pads is necessary. Therefore, the effect of ferrite cores and optimization in terms of number, length, and distance between cores in finite element simulation has been investigated. In some cases, it is necessary to use ferrite cores, so the effect of ferrite cores and optimization in this pad has been investigated. The results of analytical calculations of mutual inductance in different distances between pads have been investigated and the results of calculations verified with experimental and FEM simulation. The values calculated by the practical method and simulation with good accuracy verify the analytical model.

In this article, the design of a miniaturized narrow-band terahertz absorber is theoretically investigated. The designed absorber is made of an artificial dielectric layer (ADL) deposited on a substrate terminated by a metallic layer. The ADL includes two thin metal layers vertically separated by a thin dielectric film. Each metal layer is patterned to form a lattice of disconnected squares. The lattices on the two metal layers are shifted with respect to each other so that each square on the top lattice partially faces four squares on the bottom lattice. With a proper design of the structure parameters and utilizing the capacitive nature of ADL and the inductive property of the grounded dielectric spacer (substrate terminated by a metallic layer), the resonant frequency can be achieved at the terahertz regime. In this paper, a simple circuit model is presented for surveying the absorber behavior at normal incidence. The designed absorber shows perfect absorption around a center frequency of 0.4 THz with a quality factor of Q = 20. The proposed structure is polarization insensitive and shows absorption stability over a wide range of oblique incidence angles. Furthermore, the size of the proposed absorber is very smaller than other metallic absorbers at low terahertz frequency. The thickness of the structure is and the size of the unit cell is . Finally, a dual-band absorber can be realized using two layers of ADL.

Resolver is a position sensor for determining the rotational or linear position. Optimal design of resolver needs an accurate and computationally fast model. Such model for linear resolver must also be able to take longitudinal end effect into account. Therefore, in this paper, an analytical model based on subdomain method is proposed for linear resolver. The presented model, not only considers the longitudinal end effect of the stator and mover, but also takes the cores’ slotting effect into account. The results of the proposed model are verified by comparing them with the results of finite element analysis and experimental measurements on the sensor’s prototype.

In this paper, an avalanche photodiode (InGaAs/Si SACM APD) for detection at 1550 nm is presented. This detector has a simple structure, defined in terms of layers and its main detection parameters such as dark current, photocurrent current, gain and responsivity are optimized. The advantage and distinction of this detector is that its bias voltage is smaller than the models available in the references and its detection parameters can compete with them. This bias voltage is at least 41% lower than other adaptive references in similar conditions. In the index (0.9V_br), the photocurrent is8.3 u A and the dark current is 4.9 nA. At a bias voltage of 25 volts, the photocurrent and the dark current to 51 u A and 21 nA increase compared to the same photodiode. This detector can also be used for special applications that require very low dark current.

In this paper the co-site interference in systems involving multiple radios has been studied. This type of interference occurs when a receiver is receiving a weak transmitting signal in the presence of transmitters or even high power jammers. Components of this interference include the power spectrum of the transmitter output, the electromagnetic coupling between the antennas, the level of sensitivity of the receiver and possible intermodulations between different frequencies in the co-location system. Frequency and amplitude of interference at the input of receivers are calculated and reported by providing software in MATLAB. In this software, radio transmitters and receivers and their antennas can be modeled based on factory information, simulation and measurement.

Since the early twentieth century, electrostatic precipitators have been recognized as an important industrial technology and have been used as air pollution control devices in industrial applications such as cement plants and diesel engine generators. Despite the high overall efficiency of electrostatic precipitators, the fractional efficiencies for submicron particles are lower than that of larger particles. On the other hand, the laws on particulate matter injected into the ambient air by industrial processes have become increasingly stringent (for example, a 30 percent reduction in the amount of particulate matter emitted by Chinese thermal power plants from 2012 to 2014). Therefore, the need to take precautions to improve the performance of this equipment in the face of these particles is felt more than ever. In this paper, by presenting formulations related to various processes within electrostatic precipitators and their three-dimensional numerical modeling, the electrical and electrohydrodynamic properties as well as, the submicron particle collection efficiencies for a precipitator in laboratory dimensions with different spiked electrodes are investigated. For this purpose, airflow lines and particle collection efficiencies with a diameter of 0.25 to 1.5 μm for bidirectional and unidirectional spiked electrodes have been evaluated and compared. The results indicate that for particles with diameters of 0.25 to 1.5 μm, the two-side spiked electrode is the best discharge electrode arrangement for collecting submicron particles. The effect of particle mass flow rate on the deposition efficiency of fine particles for a two-side spiked electrode has also been investigated. The simulations show that the particle deposition efficiency decreases with increasing particle mass flow rate at the inlet.

In the presented work, a new rotor circuit is proposed for a brushless doubly-fed induction machine (BDFIM) with 8-/4-pole power/control winding. Using the proposed rotor circuit, the mutual-coupling of the power winding and the rotor circuit, and consequently the cross-coupling between the power and control windings is increased. Therefore, a BDFIM with a higher torque capacity is obtained. A dynamic model is established for BDFIMs and used as a fast tool to investigate and compare the characteristics of the proposed machine with the extant BDFIMs with parallel and series loops. The dynamic model is funded based on the concept of multiple coupled circuits. The machine magnetizing inductances are the parameters of this model and obtained by using the winding function method. The provided dynamic model is validated by means of time-stepping finite element analysis. Finally, it is shown that using the proposed rotor circuit, the cross-coupling of the stator windings is increased. Consequently, the magnetizing current and the Joule losses are decreased in the proposed BDFIM machine.

Nowadays electromagnetic systems are increasingly used in industrial servomechanisms. Those systems are usually working with two-degree of freedom and their actuators employ Permanent Magnets (PMs) to improve the power density requirements. The position of the moving part’s center is required for optimal electronic commutation and control of the PM actuators. In this paper, determination of the coordinates of the mover’s center using 90-degree linear Selsyns (linear resolvers) is examined. Linear resolvers are position sensors that are compatible to work in harsh industrial environments. However, there are some challenges in using two individual linear resolvers for such applications. Therefore, in this paper after discussing those challenges, a new configuration is proposed to overcome them. The success of the proposed planar resolver is verified by 3-dimentional time stepping finite element analysis and experimental measurements.

The electric field is one of the main factors which causes corona discharge and the insulation defect of high ‎voltage insulators. Therefore, the voltage distribution and electric field calculation along the insulators is ‎important for the design and development of transmission lines. Depending on the construction position, ‎suspension insulators are connected at a certain angle to the vertical line. This is called insulator string ‎deviation. The insulator string deviation can change the electric field distribution of the insulator string. In ‎this paper, the insulator string offset effect on the electric field distribution of a 230 kV suspension insulator ‎string has been simulated. The insulator string has been simulated in COMSOL software based on the finite ‎element method. The effects of 15 and 30-degree insulator string deviations have been investigated on the ‎electric field distribution, insulator string efficiency, and the effective length of the insulator string. Then, ‎the results have been compared with the insulator string without offset. The simulation results show a ‎significant effect of the insulator string deviation on the electric field and voltage distribution of the ‎insulator string. Also, the effect of insulator string deviation on the effective length of the string and its ‎dielectric strength has been significant.‎

The energy from electromagnetic pulses causes disruption and failure of electronic systems used in radars and communications equipment sush asthe ELINT system. The rate of influence of high-powered electromagnetic waves and their electric fields on the equipment depends on two parameters: the intensity of the electric field and the target coating method....the plasma is one way to protect against electromagnetic threats. When an electromagnetic pulse is propagated through a plasma limiter, the charge particles accelerate, and the magnetic field generated by the electromagnetic wave can change the state of the gas to plasma. In this paper, the design theory of a plasma limiter based on a new structure in 1.8 to 2.8 GHz is presented. By introducing various power generation sources, numerical analysis, simulation and optimization of plasma limiter are investigated and the prototype of plasma limiter is tested to protect the ELINT receiver in the frequency range of 1.8 to 2.8 GHz at 1200 and 1800 w. The measured results show that the return loss is better than -10 dB in 1.8 to 2.8 GHz. After optimizing, the value of h was obtained in 19 mm and the value of n was about 46 mm, which in the constructed sample, we placed it at 47 mm, ie exactly in the center. The laboratory results during high power pulses show an excellent agreement with respect to finite element method.

In this paper, a 3.1 to 10.6 GHz low noise amplifier has been designed using 130 nm CMOS technology. In this circuit, the source degeneration technique is employed to increase the bandwidth and achieve input impedance matching as well. In addition, a current reuse technique is employed to achieve a high gain. Since most output impedance matching techniques degrade gain or linearity, an inverter along with an inductive peaking technique is used to provide output impedance matching of 50 ohms and to improve both linearity and gain. This technique enhances the third harmonic behavior and increases the gain by 2.7 dB. The proposed circuit achieves S11 of less than - 9.1dB, S22 of less than -10 dB, the maximum gain of 19.7 dB, NF of 2 to 2.7 dB, and IIP3 of -3.5 dBm. Moreover, the power consumption of the proposed circuit is 28 mw and the core layout size is 991.84 μm×701.4 μm. The advantages of the proposed circuit over UWB structures with the same technology are higher gain, lower Noise Figure, and better output matching.

In this paper, the performance of a high-sensitivity, low-cost, low-dimensional Fabry-Perot based fiber-optic sensor for measuring argon gas pressure is reported. A Fabry-Perot sensor probe with an air cavity, length of 1.25 mm and suitable diaphragm with different thicknesses has been investigated in order to achieve the optimal thickness. The ultimate goal is to achieve a diaphragm that detects and measures gas pressures below 80 millibars. A PVC layer was used as second Fabry-Perot plate of the sensor,The sensing experimental arrangement for measuring gas pressure was provided in the laboratory. The effect of gas pressure as well as diaphragm thickness as an important parameter on the sensitivity of gas pressure sensor was investigated. Diaphragm thicknesses of 42, 56 and 70 μm and cavities with a length of 1.25 mm were investigated at different pressures of argon gas. The results showed that the best sensitivity with a value of 0.035 nm / mbar is related to the sensor with a diaphragm thickness of 42 μm.