نشریه مهندسی برق
سال چهل و سوم شماره 2 (پیاپی 66، پاییز و زمستان 1392)

In this paper, we present a new design of a high directive electromagnetic band gap (EBG) resonator antenna that utilizes a single layer of a taper compact uniplanar-compact EBG (UC-EBG) as a superstrate. The influence of EBG superstrates over return loss of the probe-fed micro strip antenna (PFMA) has been studied. It is required to have proper impedance matching to increase the efficiency of the whole structure, including the PFMA and EBG superstrate. The different operating frequencies by adjusting the distance of superstrate layer from printed patch antenna are obtained. The final design have a bandwidth of about 12% with directivity more than 14dB.

Today, using inductively coupled contactless power transmission systems (ICPT) to charge electric vehicles is a promising step in increasing efficiency of electric vehicles. In this paper, the design of an ICPT systembased on a rectangular coil configurationfor primary and secondary coil is presented. An analytical model of the contactless power transmission system is derived and is used tooptimize the performance of the system.System parameters are optimized using artificial bee colony algorithm and a new two-objective optimization problem is obtainedwhich optimizes the system parametersto reachmaximum efficiency while the minimum volume of copper is needed to be used. Moreover,the necessity of compensation in both primary and secondary studied and the best compensation technique based on the application of ICPT system is applied.The designed system performance while the primary and secondary windings are misaligned is investigated.Simulationsare done by MATLAB and ANSOFT MAXWELL and the results confirm theanalytical model and designed result as expected.

In this paper, a new method is proposed to modify the function of distance relays in protection of short transmission lines. Besides having numerous advantages, distance relays have also some disadvantages which are more serious in the case of short transmission lines. Effect of fault resistance and small voltage in the relay point are the most important problems of relays in such lines which lead to large CVT errors. In this paper a new method is proposed for overcoming mentioned problems and using it, will improve distance relays function. Effectiveness of the proposed methods is assessed, analyzed and compared with the existing methods, using simulations in EMTP software.

In this paper, primarily, a new photonic crystal fiber (PCF) structure is proposed in which a large anomalous group velocity dispersion (GVD), single mode operation, small higher order dispersions (HODs) and enhanced nonlinear characteristics for ideal generation of ultra-wide band spectra and femtosecond ultra-short optical pulses applying subnanojoule input pulse energy in the low loss wavelength of 850nm is presented. Furthermore, numerical simulations are presented to show that the bandwidth and the intensity of generated optical pulses increase dramatically with positive chirp. Finally, optimal values of positive chirp parameters are identified in the novel PCF structure that maximize the bandwidth and intensity of optical pulses respectively.

In this paper, a new steganography method is provided to embed the secret data into the least significant bits of host pixels. Data extraction process from the host image is independent of the original image. Before the embedding process, the secret data are encoded using a Reed-Solomon block error correction code. Therefore, the proposed algorithm is able to correct errors resulting from intentional or unintentional damages created on stego-image during the data extraction. Also after encoding, in order to reduce the mean square error (MSE) between the images before and after embedding, data are embedded into the least significant bits of host pixels using optimal substitution table and modulus function. This diminished MSE improves the visual quality of the stego-image meaningfully. Since the proposed method is able to embed data into more significant bits preserving the visual quality of the image, it has enhanced the embedding payload. The simulation results show that the proposed algorithm not only increases the embedding payload, but also increases robustness to attacks by increasing error correction capability, in comparison with similar methods.

In this paper, a long-term distribution system planning model is presented considering technical and economical constraints. The proposed optimization model studied distribution system planning in a competitive environment, considering all network equipments including feeders, substation, intertie and DISCO-owned or SPP(small power producer)-owned DGs in different technologies and created a comprehensive framework for long-term distribution system planning according to the planner experimental decisions. Presented cases in electrical market tested on 32 bus distribution system confirm the effectiveness of the proposed model and have investigated the impact of existence of different energy sources in system operation and economics.