نشریه الکترومغناطیس کاربردی
سال چهارم شماره 1 (پیاپی 10، بهار 1395)

Brushless permanent magnet motors have considerable advantages and have been found with many applications. Despite the acceptable efficiency, the output torque ripple is the main drawback of motor performance.
In this article, the effect of air gap flux variation on cogging torque is investigated. Various dimensions of the slots in permanent magnet’s stator tooth is created and cogging torque variation is investigated using a finite element method. Proper slot shaping is suggested and the core loss variation is investigated.

In this paper, firstly, a new idea of obtaining the electromagnetic image of large objects has been investigated. Then, the distributed target has been simulated in software and results have been processed to extract 2-dimensional image of the target model. Therefore, for the first time, the simulator gains the capability of distributed targets simulation that is required for the SAR simulator. The next achievement is the simulation of sea clutter that has been simulated for forward-looking radar, with respect to the requirement of SAR to the clutter, for Doppler centroid and Doppler rate extraction and the need for considering sea fluctuations for the first time. The advantage of this method is considering the radar movement in radar raw data. It is because SAR processing algorithms use radar raw data to estimate radar velocity and acceleration. Also, with respect to the motion of sea waves, the clutter has significant bandwidth in the azimuth direction. This property has been used for the application of a new idea whose benefit is reduction of needed points for simulation.

Recently, circular polarization ultrawideband (CP UWB) antennas have received significant attention in microwave imaging. In this paper, the use of a UWB logarithmic spiral antenna with circular polarization for tumor detection is proposed. One of the main advantages of UWB antennas to narrow-band (NB) antennas is its higher resolution. The absorption of more scattered fields is also the advantages of circular polarization antennas to linear polarization antennas. Compared with the conventional spiral antenna that uses coaxial cable for feed structure, to improve the performance of radiation characteristics, tapered microstrip to stripline balun is used to feed the two arms of spiral antenna. The measured results show that the return loss is better than 10 dB from 3/1 to 10/6 GHz. Also the radiation pattern is bidirectional with circular polarization in the entire bandwidth. The time-domain characteristic of the transmitting and receiving system using the proposed spiral antenna with studying two parameters fidelity factor and group delay is investigated. Results show that for proposed antenna, the fidelity factor is higher than 0/91 and group delay less than 1/0 5 nsec. Construction and measurement of the proposed spiral antenna for use in tumor detection are presented.

Frequency diverse array (FDA) is a new antenna array concept that is different from phased-array which offers range independent beam pattern. FDA using linearly increasing tiny frequency increment yields an S-shaped range-angle radiation pattern. This enables the array beam to scan without the need for phase shifters or mechanical steering. It is possible to apply different frequencies with different patterns to the elements of FDA to achieve different radiation pattern. However, the FDA transmit beam pattern is coupled in range and angle dimensions. It has been shown that the beam pattern of this form of FDA is range-angle-dependent, and it exhibits maxima at multiple range values. In this paper, we propose a single dot-shaped beam pattern analysis using symmetrical FDA with non-uniform inter-element frequency offset called elliptic-FDA. To validate the proposed approach, simulation example of non-uniformly elliptic based exited symmetrical FDA are reported and discussed.

In this paper, influence of coil steps on the induction heating process has been computed using the Finite Element Method (FEM). At first, a single-turn coil with axisymmetric (no step) has been considered, and then the coils with 3, 5 and 7 cm steps have been employed. Voltage 200 volt with frequent of 1 KHz has been used, which it applied to the coil, as source of electromagnetic fields. The results of the calculations show that distribution and intensity of electromagnetic fields, eddy currents in the workpiece, and generated volume heat in the coil and workpiece for the coil without step have a significant difference with other coils (i.e. the coils with steps of 3, 5, and 7 cm).

In this paper, a new design of a broadband high gain circularly polarised slot array antenna (CPSSAA) is presented. The proposed antenna is fed by a symmetric hybrid coupler for C-band application. The designed single array element is excited by L-shaped strip with a tapered end, located along the circular-slot diagonal line in the back plan. From the single array element simulation results, the -10dB return loss bandwidth is around 8.79GHz (2.51GHz-11.3GHz). The designed single array element is 50% wider than the impedance bandwidth of a previous similar design. The proposed antenna is composed of 2 × 2 Array elements. The measured results for The final structure of circularly polarised slot array antenna are about 54% (3.5GHz-6.5GHz) for return loss BW, 22% (4.4GHz-5.4GHz) for axial ratio and peak Gain around 12.45dBic at 5.5GHz. The simple structure, light weight, compact size, circular polarization with a very high polarization polarity and a high gain, make it a perfect match for C-band applications, in which a circular polarization antenna is required. The measured results corroborate well with the simulated results.