JOURNAL OF APPLIED ELECTROMAGNETIC
Year:2019 | Volume:7 | Issue:1 (18)|Papers Count:12

In this paper a low profile, low-cost smart antenna which has a high gain and high radiation pattern diversity is presented. This antenna is actually an advanced ESPAR antenna which is made up of a “ short monopole” and 12 “ folded monopoles” . The short monopole is in the center and is used as the driven element and the 12 folded monopoles are used as parasitic elements. The coupling between the driven element and the parasitic elements creates a capacitive load for the driven element, which causes the antenna to become low-profile. By turning on and off 12 "PIN diodes" at the bottom of the parasitic elements, the beam can be rotated. The dimensions of the proposed antenna fabricated in the S band are reduced by 30% compared to the conventional smart antennas of this band. The antenna height is less than 24mm (0. 186λ @ 2. 4 GHz), the front to back ratio is 22. 4dB and antenna's maximum gain at 2. 4GHz is 8. 26dBi.

In this paper, the effects of silver ribbon nanoparticle dimensions and the refractive index of the environment on silicon solar cell performance are investigated and analyzed. By changing the dimensions of nanoparticles and altering the refractive index, important parameters such as efficiency are simulated with finite-difference time-domain (FDTD) method. Also, the solar cell performance is investigated with and without nanoparticles. By changing the nanoparticle dimensions, the optimum case to achieve maximum efficiency is obtained. The influence of changes in refractive index of the environment from 1 (air) to 1. 6 on the performance of the solar cells and the coupling profile are also studied. The simulation results reveal that the efficiency of 12. 45 is obtained by selecting a refractive index of 1. 2.

This research describes the optimum design of a Miniaturized Electromagnetic Generator (MLG) which supplies electrical energy for the projectile fuse. It supplies the energy by converting the mechanical energy of the projectile into electrical energy. The MLG presented, consists of three parts; a ring magnet, a metal bobbin, and a shear plate and produces the energy by applying the Faraday induction law. To maximize the energy and determine the effect of each parameter on the energy, optimization was performed using RSM, while numerical simulations were performed by Maxwell 3D. Having obtained the MLG parts’ optimum dimensions, an experimental test was used to verify the numerical results. Due to the mechanical energy of the projectile resulting from the initial acceleration, the shock test was selected as the experimental test. The results obtained in the 800'g acceleration range with a capacitor of 100uF show the charge rates of 14V in 1. 9ms and 14. 8V in 1. 5ms for the experimental test and the numerical method respectively, displaying good conformity between them. Also, a safety mechanism was designed to activate MLG at accelerations higher than 800'g and its analysis was carried out by Abaqus. In addition to reducing the volume, the results of the optimization led not only to increased energy production by MLG, but also, to the determination of each part’ s effect on the MLG's performance.

A new topology for the design of microwave narrow band-pass filters (NBPFs) with wide out of band rejection and sharp edges, based on the use of Composite Right-Left Handed (CRLH) Transmission Line (TL) concept is presented. The proposed NBPF has been realized by using two different sections. The left-handed section is implemented by etching spiral complementary split ring resonator (SCSRR) unit-cell in the ground plane as well as series interdigital capacitors in the upper metal level while the right-handed section is implemented by etching SCSRR unit-cell in the ground plane and conventional microstrip transmission line shorted via a hole in the upper metal level. Accordingly, CRLH transmission line concept is implemented by this configuration which acts as a narrow band-pass filter. Because of the smaller electrical size of spiral resonators, the total electrical size of the proposed NBPF can be reduced by using this proposed configuration. Compared with some other reported NBPFs, the presented NBPF has great improvements in size reduction and selectivity. Consequently, a compact NBPF is designed which exhibits extremely sharp rejection skirts around the target passband. The equivalent circuit model of the designed filter and full-wave simulation results of the NBPF are also developed. To validate the design concept, the proposed NBPF has been fabricated and tested. Experimental verification is provided and good agreement has been found between simulation and measurement. The proposed NBPF has a passband which covers 2. 25 to 2. 45 GHz and its measured 3 dB fractional bandwidth is about 8. 5%. The total size of the proposed NBPF is 0. 25 λ g× 0. 06 λ g, where λ g is the guided wavelength at the center passband.

The rotor structure of a synchronous reluctance machine (SynRM) engages some design complexities. These complexities have made it impossible to employ a generalized design method valid for all machine topologies with various number of rotor and stator slots till now. However, using trial and error and optimization algorithms such as genetic algorithms, etc., an optimal design is obtained which is both time consuming and complicated. Indeed, high amount of ripple in the developed torque is a serious problem of SynRMs, which could be reduced by employing an effective design method. This paper presents a new SynRM rotor analytical design method with the aim of reducing torque ripple while maintaining average torque. To this end, the proposed method is applied to a SynRM with 24 stator slots and 2, 3, and 4 rotor flux barriers. In order to evaluate the proposed method’ s effectiveness, three designed SynRMs’ electromagnetic performances are simulated using finite elements method (FEM). It has been shown that the design parameters resulted by the proposed analytical method is close to the optimal state obtained by preceding time-consuming complicated methods.

In this paper, a metamaterial based toroidal ferrite phase shifter design algorithm has been introduced in X band. For the design of such a phase shifter, first the MNG (negative μ ) ferrite core in extraordinary bias mode should be implemented. Then, the ENG (negative ε ) part composed of parallel metallized lines should be designed on a substrate board. Finally, the input and output port impedance matching could be accomplished by using two section dielectric step transformers layout using binomial tapering method. According to the simulation results, the closed toroidal ferrite core shape, has treated the main disadvantage of metamaterial waveguide phase shifter’ s experimental bias complications, and it has reduced the amplitude of magnetic bias filed from the typical range of (6-7 kOe) to under the acceptable 100 Oe value, which could be achieved using a simple wire. Moreover, by introducing a new core structure and an impedance matching network in the proposed phase shifter, the second main disadvantage of the metamaterial-based ferrite phase shifter which is their high insertion loss, has decreased from 10 dB to 3. 2 dB.

Since railgun is an electro-mechanical system, it is not easy to simultaneously solve the electrical and mechanical equations. In this paper, a method based on a circuit model is presented for the analysis of the railgun, in which, its equivalent circuit is extracted and the differential equations describing its behavior are obtained. Using the 4th order Runge-Kutta method solution to theses equations, railgun simulation is performed. The main advantage of the proposed method is that due to its calculation speed, it can be easily used in the sensitivity analysis and design optimization, while these issues are almost impossible with finite element method, due to their slowness. Then, by employing the proposed method, the system has been simulated and its behavior has been studied. Also, the effect of the railgun structural parameters’ variations on the velocity, efficiency and force applied to the armature has been investigated. To validate the proposed method, the point to point 3-D finite element method is employed. The results of the finite element method are close enough to the results of the proposed method, confirming the accuracy of the latter.

In this paper, a new driving method is presented for a magnetron bulb utilizing a phase-shifted active clamp fly-back converter. The converter is of a booster, isolated and high gain type. The active clamping structure is used to reduce the main transistor’ s voltage stress. By controlling the timing of the transistor clamp, the voltage required for the magnetron is adjusted. The main advantage of the proposed method is the simplicity of the control circuit of the magnetron lamp driver. In addition, the proposed method reduces the size, weight and price of the power transformer core. The power transformer leakage inductance has also been developed to provide a soft switching condition while reducing converter losses. The converter presents a maximum power of 1. 6 kW with an average power of 400 W, by setting the timing of the activation of the driving circuit. The design results are simulated and verified by PSCAD Simulink software.

Circular polarization is one of the most popular polarization approaches used in different communication systems such as radar, satellite, GPS and WiMAX systems. In this article, we want to design a wideband cylindrical antenna with circular polarization and maximum frequency coverage from 1. 7 to 2. 7 GHZ. If the optimum load impedance of the amplifier at different frequencies are close, the antenna can be used as an optimal load for the amplifier. In this paper the output of the antenna after application of signals in the S band is also investigated and the effects of the antenna radiation on the amplifier circuits have been considered to some extent.

Statistical models are employed to represent both clutter characteristics and reflecting signals in the radar and telecommunication receivers. Rayleigh distribution is the simplest fading model in NLOS channels whose accuracy is lower than required in high-resolution radars and distant telecommunication receivers. At present, high accuracy models such as the m-type Nakagami and hybrid K and GK distributions are utilized in order to model fading. Although in NLOS channels, Non-Rayleigh models have better precision than Rayleigh models, the accuracy of these models decreases when the radiation angle in the transmitter and the reflection angle in the receiver are different. Whilst the K model has previously been introduced to describe the clutter properties of the radar, in this paper both K and F distribution functions are analytically introduced and deployed to model the fading using practical data.

The magnetic crane is an example of industrial applications of magnetic absorption in which an electromagnet is used to create the necessary magnetic force for lifting and moving objects. There are various structures for the shape of electromagnet’ s core, but studies show that the U_I structure with a symmetrical winding is the most appropriate one in terms of reducing the loss due to leakage flux and fringing effect. The purpose of this paper is presenting a novel method for field analysis and designing an electromagnet. Focusing on the leakage flux and fringing effect, and taking into consideration the nonlinear behavior of the B-H curve and saturation point of ferromagnetic core, a new magnetic equivalent circuit for the electromagnet is proposed. For numerical analysis and design of the electromagnet, the Matlab software and for simulation of its magnetic field and force, the ANSYS MAXWELL software has been used. To verify the accuracy of the presented method, the prototype of an electromagnet has been made, in accordance with the design parameters extracted from the proposed algorithm. The comparison between measurements and simulation results show that the error is less than 2%, which confirms the accuracy of the proposed method.

Laser interferometer system is a diagnostic tool used to measure the electron density in the tokamak plasma. The system consists of various components such as the laser, the detector, the optics, the control unit and data acquisition unit, etc. The first step in setting up the system for experimental purposes is to characterize each of its components according to the tokamak parameters and the research goals. The laser is one of the most important components of this system and once chosen, affects the selection of other components. For this reason, this component has been the first to be studied in Damavand tokamak system. The laser wavelength can be selected from microwave to far-infrared and infrared regions depending on the plasma volume, the magnetic field and electron density. In this paper, laser characterization is accomplished by means of identifying sources of error in the measurement of electron density in the Damavand tokamak plasma. Resolution of two-color laser interferometer, refraction phenomenon, Faraday rotation effect, vibration limit, transparency of the vacuum window for laser wavelength, the noise due to the compensation wavelength and the extraordinary mode propagation are identified as the sources of error in density measurements. Then, the wavelength dependence on these phenomena is found. Results indicate despite the fact that the dual CO2 laser system is poor at effective phase resolution, density resolution and the signal to noise ratio, in comparison with other combinations of laser wavelength, its small refraction, tiny Faraday rotation angle and more stable interference signal make it a suitable choice for electron density measurement in Damavand tokamak.