فهرست مطالب

  • Volume:6 Issue: 4, 2018
  • تاریخ انتشار: 1396/10/30
  • تعداد عناوین: 6
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  • Shahrouz Nasiri, Mehdi Tabasi, Alireza Bakhshinejhad Pages 99-104
    Strike of lightnings with sea, due to the high conductivity of salty water creates more extreme electromagnetic fields in comparison with lightnings in land. This paper deals with analysis and simulation of electromagnetic fields resulting from lightning in the proximity of a watercraft in sea and its effect on the equipment on the watercraft. The magnitude of electric and magnetic fields is first calculated using Uman integral equations to calculate the electric field resulting from a limited current channel on a perfect conductor. To solve the field integrals, dual precision exponential model was used for the lightning’s current. Due to limitations of the solution of field integrals, parametric analysis is difficult. For this reason, the lightning channel and watercraft model was simulated in Maxwell software and the obtained fields were compared with the results of integral solution. Considering the closeness of integral and simulation results, with alteration of the peak lightning current and its distance off the watercraft, the field sensitivity to these variables was measured and the results of parametric analysis have been presented for different parts of the watercraft.
    Keywords: electromagnetic field, lightning, watercraft, sea, Maxwell
  • Maryam Samadpour Hendevari, Mohammad Bemani, Saeid Nikmehr Pages 105-108
    In this paper, a wedge-shaped invisibility cloak whose diameter gradually increases along the arms of the wedge is introduced. The constitutive parameters of the cloak are obtained using a proper transformation. By considering two special cases for incident fields, (TEz and TMz), and paying attention that the wedge structure is invariant in axial and radial directions, the reduced set of cloaking parameters are obtained spatially invariant and larger than one, keeping the PML (perfectly matched layer) condition for perfect cloaking performance. Spatially invariant and isotropic constitutive parameters lead to the physically realizable cloak in a wide band of frequency for this specific type of incident fields.
    Keywords: Microwave Cloak, Transformation Optics
  • Majid Malekian, Hossein Emami, Mohsen Ashourian Pages 109-114
    Today, In Communication world, optical access networks play a fundamental role to secure and offer a wide band width to customers. Therefore, this use of communication ground of optic fiber, because of little diameter of optic cable rather than copper cable and undeniable capabilities of optic networks, is a new discussion of communication world of our country. In this regard, the way of optimum utilization of optic transition systems to residence location of customers with the minimum cost and the maximum capacity is the most important discussion of this matter that use of fiber to common house (FTTH) is an appropriate case for discussion, and with decrease of common access distance to fiber to the intended location, it makes facilities and advantages available for customers. The aim of this paper is explaining the parameters of an optic communication system to be able to determine and select the optimum communication system according to peripheral conditions, technical work range, and calculation of amounts of systemic parameters are determined in case with aim of access to desirable OSNR and increase of capacity of optic communication channels.
    Keywords: Optic access networks, Systemic specified parameters, OSNR, Channel capacity, fiber to common house
  • Omid Sharifi-Tehrani Pages 115-118
    A frequency hopping spread spectrum data link that works in the unlicensed frequency band of 2.2 GHz to 2.3 GHz, needs to be compliant with EMI/EMC Issues to reject or attenuate the unwanted input signals (interferences) and also preventing of spreading out spurs and harmonic signals. Because of unlicensed band and no affordable commercial filters, two types of microstrip band pass filters called hairpin and interdigital were designed, simulated and fabricated on FR4 substrate as application specific filters. The results showed achievement of needed performance.
    Keywords: Microstrip Band Pass Filter, Hairpin, Interdigital, EMI, EMC, Interference Rejection, Spur Attenuation
  • Parisa Fallah, Bijan Zakeri, Amirashkan Darvish Pages 119-125
    Ground penetrating radar (GPR) is one of the most important instruments in some cases such as remote sensing, non-destructive evaluation and microwave imaging. The radiation component (antenna) in these radars is very important. Features and constraints such as high impedance bandwidth, stable radiation patterns, minimum distortion of the antenna end reflections and consequently sending high-precision pulses makes many challenges in construction and design of the antenna. In addition, the antenna size, which is expected to cover both low frequencies and portability, adds to the difficulty of designing this antenna. In this paper, four possible modes of wire bowtie antenna, which is known as one of the most common antenna in impulse GPR applications are introduced and investigated. To this regard, late-time-ringing effect of the transmitted UWB waveform, pattern characteristics and impedance bandwidth of the proposed structures have been analyzed and compared. The results show that the other modes can be replaced to the original one in most cases.
    Keywords: Bowtie antenna, Ground penetrating radars, Wire structures, UWB pulse radiation, GPR antenna, input impedance, GPR pulses, radiation pattern
  • Shahrouz Nasiri, Mehdi Tabasi, Alireza Bakhshinejhad Pages 127-133
    This paper deals with modeling and investigating transient overvoltage resulting from lightning in medium voltage grid and transferring it to low-voltage grid inside watercraft during berthing and connection of the grid in the coast. Lightning wave transfer through distribution transformer has been considered taking high-frequency model of transformer into account for passage of impulse wave. The effect of high-frequency model obtained from the transformer has been compared and validated using capacitive π model using previous measurements. The effect of different quantities of the system for connecting coast power to the watercraft including length of the connection cable, the loads on the watercraft network, type of loads, and effect of transformers’ secondary on the watercraft was examined on the level of transient overvoltage on low-voltage loads. Determining the primary and secondary overvoltage levels of transformers allows for specifying the protective level of arrestors for insulator protection coordination. This protective level, which has been obtained from IEEE lightning arrestor selection guideline, has been employed to determine the suitable values of the lightning arrestor for coast to watercraft power connection system.
    Keywords: transient overvoltage, transformer high-frequency model, coast to watercraft power connection, lightning wave transfer in transformer