نشریه الکترومغناطیس کاربردی
سال سوم شماره 2 (پیاپی 7، تابستان 1394)

In this paper, a novel scheme for depth estimation of a buried conductive sphere as a metallic mine using electromagnetic induction (EMI) data is presented. In electromagnetic induction method, the transmitter coil produces the incident magnetic and electric fields that obey the Maxwell’s equations. In the receiver coil, the received response is created in two modes. Eddy-current mode ( ec V ) is derived from the perfect conductor placed in the shallow depth and another mode called current-channeling response ( cc V ) which depends on the conductivity of the medium. As expected, these responses differ depending on the direction of the incident field related to the receiver coil’s axis. There is a case that the transmitter coil’s axis is parallel to the ground surface and only the eddy current response is measured in the receiver coil. By defining the maximum value of , ecV ,the problem with depth determination transformed into the problem with finding a solution for a nonlinear equation of the form   0 zf .The method is applied to synthetic data with and without random errors. In all of the cases examined, the maximum error in depth is less than 6%.

An optimal beam forming method is proposed which incorporates all electromagnetic characteristics of the antenna elements, including radiation pattern, mutual coupling and radome effect. The optimal beam forming technique minimizes the total power radiated by the antenna array while the response in a desired direction is maintained. By considering the active element patterns efficient beam forming algorithm is obtained which is able to manage all mutual coupling effects. Simulation results show the performance of the proposed algorithm applied to an antenna array.

Line start permanent magnet synchronous motors possess many attractive features including high efficiency, low loss, high power factor, small volume and light weight. Also they need no inverter for starting which is economical for many single speed applications such as most fans, pumps and compressors. Therefore LSPMS motors have been considered as an alternative for induction motors, but the starting performance of LSPMS motors have been a challenging issue concerned by many researchers so far . Compared to Induction motors, because of braking torque due to permanent magnets, the winding space harmonics and their negative impacts on LSPMS motors torque characteristics should be considered more serious. In this paper, first the mmf distribution of stator winding in the air gap is studied based on Fourier analysis. Then by using an optimization process, a new stator winding has been developed, which has a lower harmonic content in its mmf than the conventional winding. Finally the method is applied to an existing LSPMS motor and its performance is obtained by a finite element analysis.

In this article, a radial magnetic flux density and flux-linkage of the radial flux Air-Cored permanent magnet electrical machine (RFAMP) is provided with double-sided rotor which can be calculated analytically using the sub-domain analysis. First, Analytical relationships of on load magnetic flux density and flux-linkage of this machine are presented with poisson equations and, then, these relationships are validated by finite element of numerical results in Maxwell 16.02 software. Comparisons show that the difference between fundamental components of radial magnetic flux density and flux-linkage of analytical relations and that of finite element results is less than 3%. Also, It is shown that in this machine type, even harmonics appear and the radial components of the magnetic flux density is not symmetrical, unit half cycle and Lack of attention to this subject in the design of the machine can cause inner or outer yoke magnetic saturation. In this article, to calculate the flux linkage resulting from the armature reaction, all the components of winding conductor density distribution are utilized and in the calculation of the flux linkage, all radial components of the magnetic flux density are used. In some relevant references, only the first radial component of the magnetic flux density and the second component of winding conductor are used and the other are ignored. In comparison with some related references the linkage flux and RFAPM machine inductance have been increased about 21%, that the number is significant in the study of magnetic saturation yokes. It is worth noting that the study of the comparative results has only been up to 17th harmonics and that the higher harmonics can adapt better to have the finite element results.

In this paper, a genetic algorithm-based approach for transient analysis of single-conductor overhead line connected to grounded arrester is proposed. In analysis, the grounding systems are buried in lossy dispersive soil, i.e., the electrical parameters of soil are frequency-dependent. In dealing with the problem, the lightning current pulse is first approximated by a finite set of sinusoidal harmonies in a time domain. Norton equivalent circuit viewed across the arrester is then computed via transmission line model (TLM). Finally analyzing this nonlinear circuit by genetic algorithm, transient voltage across the arrester is easily computed. Comparison of the achieved transient voltages with and without considering dispersion of soil shows that this effect plays an important role in selecting lightning arresters and the insulation coordination study of power systems. Moreover, in comparison with arithmetic operator method (AOM), the run-time is reduced.

Antennas that are installed on the aircraft, must have minimum mutual coupling so that the function of the transmitter and receiver will not be interfered. For coupling calculation, we must obtain wave pass from transmitter antenna to receiver antenna. In case that antennas are LOS, this pass is a direct pass. But in case that antennas are NLOS, a kind of surface wave causes mutual coupling. The best way for calculation of coupling is through obtaining geodesics. Then by calculation of surface loss, we can get the amount of coupling. if the aircraft is modeled with a cylinder, calculation of geodesics is easy and practical. the advantage of this approximation is that we can extend it for any aircrafts with cylindrical fuselages. in this approximation, the effect of obstacles and diffraction in edges is not considered. in this paper, results of mutual coupling calculation, results of simulation as well as the measured data is compared in approximated model of the aircraft. It will finally be shown that in the worst case, calculation results are not greater than 15db.