Vol. 13, No. 3, October 2016


Jovan M. Cvetić
Tesla’s High Voltage and High Frequency Generators with Oscillatory Circuits
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DOI: 10.2298/SJEE1603301C
Abstract: The principles that represent the basics of the work of the high voltage and high frequency generator with oscillating circuits will be discussed. Until 1891, Tesla made and used mechanical generators with a large number of extruded poles for the frequencies up to about 20 kHz. The first electric generators based on a new principle of a weakly coupled oscillatory circuits he used for the wireless signal transmission, for the study of the discharges in vacuum tubes, the wireless energy transmission, for the production of the cathode rays, that is x-rays and other experiments. Aiming to transfer the signals and the energy to any point of the surface of the Earth, in the late of 19th century, he had discovered and later patented a new type of high frequency generator called a magnifying transmitter. He used it to examine the propagation of electromagnetic waves over the surface of the Earth in experiments in Colorado Springs in the period 1899-1900. Tesla observed the formation of standing electromagnetic waves on the surface of the Earth by measuring radiated electric field from distant lightning thunderstorm. He got the idea to generate the similar radiation to produce the standing waves. On the one hand, signal transmission, i.e. communication at great distances would be possible and on the other hand, with more powerful and with at least three magnifying transmitters the wireless transmission of energy without conductors at any point of the Earth surface could also be achieved. The discovery of the standing waves on the surface of the Earth and the invention of the magnifying transmitter he claimed his greatest inventions. Less than two years later, at the end of 1901, he designed and started to build a much stronger magnifying transmitter on Long Island near New York City (the Wardenclyffe tower) wishing to become a world telecommunication center. During the tower construction, he elaborated the plans for an even stronger transmitter based on new principles. Due to lack of the funds Tesla was forced to sell or to return the devices and apparatus, he gathered in the Wardenclyffe tower facility, which intended to use to operate the tower. He left the tower in 1907 and since then he was mainly engaged in inventions that were not directly related to the electrical engineering. The unfinished magnifying transmitter on Long Island was demolished in June 1917 by the American government.
Keywords: High frequency oscillators, High voltages, Antennas, Wirelles energy transmission, Electromagnetic compatibility.

Vladimir M. Petrović, Kosta Jovanović1, Veljko Potkonjak
Dynamics Based Modeling of Wheeled Platform for Humanoid Robot Torso
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DOI: 10.2298/SJEE1603335P
Abstract: From the ancient mythology till the modern times, people were trying to build an artificial mechanical replica of themselves. Inspired by this long tradition of various engineering projects, we will hereby describe a partly humanoid robotic structure. Our robotic configuration is composed out of an anthropomimetic upper body, but instead of legs it uses a wheeled cart for the motion. In our research, this so-called semi-anthropomimetic structure has a four-wheeled cart. This work is aiming to analyze the behaviour of the robot that is exposed to different kind of external disturbances. Disturbances coming from the outside in the form of external forces (impulse and long term) simulate the interactions of the robot and its ambience. Necessary simulations were thoroughly executed (in that way analyzing robotic balance) and proper size of the cart is evaluated following the ZMP theoretical background.
Keywords: ZMP, Semi-Anthropomimetical structure, Antagonistically coupled drives, Biologically inspired robotics.

Amin Safari, Davoud Moghaddam Sheibai
Artificial Bee Colony Algorithm for Economic Load Dispatch with Wind Power Energy
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DOI: 10.2298/SJEE1603347S
Abstract: This paper presents an efficient Artificial Bee Colony (ABC) algorithm for solving large scale economic load dispatch (ELD) problems in power networks. To realize the ELD, the valve-point loading effect, system load demand, power losses, ramp rate limits and prohibited operation zones are considered here. Simulations were performed on four different power systems with 3, 6, 15 and 40 generating units and the results are compared with two forms of power systems, one power system is with a wind power generator and other power system is without a wind power generator. The results of this study reveal that the proposed approach is able to find appreciable ELD solutions than those of previous algorithms.
Keywords: Artificial Bee Colony, Economic Load Dispatch, Wind Power Generator, Valve Point Loading Effect.

Igor Fermevc, Saša Adamović
Low-Cost portable TRNG, Implementation and Evaluation
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DOI: 10.2298/SJEE1603361F
Abstract: This paper will show one of many possible hardware implementations of random sequence generators and give a short survey on existing work related to techniques used for producing true random bits. By using cheap electronic components found in every specialized store such as 8-bit RISC microcontroler, double analogue comparator chip and USB to RS232 interface integrated circuit, we were able to produce a low cost, higly portable device that outputs random sequences with excellent statistical characteristics and high entropy. The source of randomness is a mix of techniques such as electronic noise, phase noise and oscillator jitter. The device in question has a built-in debiasing algorithm similar to [1] and a security mechanism that protects the end user by constantly monitoring the quality of digitized noise signal. Finaly, we will show the results of comparative analysis of data acquired from our device and „“ online service.
Keywords: Randomness, Electronic noise, Free running oscillator, Cryptography.

Đorđe Antić, Mladen Veinović
Implementation of DNSSEC-Secured Name Servers for Zone and Best Practices
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DOI: 10.2298/SJEE1603369A
Abstract: As a backbone of all communications over the Internet, DNS (Domain Name System) is crucial for all entities that need to be visible and provide services outside their internal networks. Public administration is a prime example for various services that have to be provided to citizens. This manuscript presents one possible approach, implemented in the administration of the City of Niš, for improving the robustness and resilience of external domain space, as well as securing it with DNSSEC (DNS Security Extensions).
Keywords: DNS, DNSSEC, Security, Cryptography.

Radoslav Surla, Nebojša Mitrović, Slobodan Đukić, Vedran Ibrahimović
Amorphous Fe72Cu1V4Si15B8 Ribbon as Magneto-Impedance Sensing Element
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DOI: 10.2298/SJEE1603381S
Abstract: Мagneto-impedance (MI) effect in the Fe72Cu1V4Si15B8 amorphous ribbon obtained by melt spinning method has been studied. The aim of study was the characterisation of this ribbon in as-cast state in terms of its application as a MI sensor. The experiments on MI elements were performed in the frequency range from 30 kHz to 300 MHz and maximum external magnetic field up to 28.6 kA/m. Maximum observed MI-ratio (ΔZ = Z(0) – Z(Hmax), Hmax = 28.6 kA/m) has amounted to ΔZ/Z(Hmax) = 173% at a frequency of 20.46 MHz. The MI curve measured up to 20 MHz shows some shoulder indicating the growth of rotational contribution of magnetization that appears above the domain wall relaxation frequency. The MI profile at frequencies higher than 30 MHz, exhibits a clear peak positioned at transverse anisotropy field Hk, suggesting domination of rotation magnetization in transverse permeability. The linearity in the range up to 5 kA/m with sensitivity of about 11 %/kA/m was observed.
Keywords: MI effects, MI sensors, Amorphous alloys, Magnetic field.

Milica I. Petković, Goran T. Đorđević
Performance Analysis of Coherent FSO System with SSC Receiver
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DOI: 10.2298/SJEE1603395P
Abstract: This paper analyzes the performance of coherent free-space optical (FSO) system employing the switch-and-stay (SSC) dual diversity receiver. The intensity fluctuations of the optical signal are modeled by Gamma-Gamma distribution, being caused by atmospheric turbulence. In addition, pointing errors are taken into account. Novel analytical expressions for the outage probability are derived. The general scenario of unbalanced average signal-to-noise ratios (SNRs) of independent and identically distributed SSC branches is considered, which is further simplified to the balanced SNR case. The effects of various system and channel parameters are investigated and discussed.
Keywords: Atmospheric turbulence, Free-space optical (FSO) systems, Outage probability, Pointing errors, Switch-and-stay (SSC) diversity.

Marija Blagojević, Živadin Micić, Momčilo Vujičić
Cluster Analysis of Knowledge Sources in Standardized Electrical Engineering Subfields
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DOI: 10.2298/SJEE1602265J
Abstract: The paper presents a cluster analysis of innovation of knowledge sources based on the standards in the field of Electrical Engineering. Both local (SRPS) and global (ISO) knowledge sources have been analysed with the aim of innovating a Knowledge Base (KB). The results presented indicate a means/possibility of grouping the subfields within a cluster. They also point to a trend or intensity of knowledge source innovation for the purpose of innovating the KB that accompanies innovations. The study provides the possibility of predicting necessary financial resources in the forthcoming period by means of original mathematical relations. Furthermore, the cluster analysis facilitates the comparison of the innovation intensity in this and other (sub)fields. Future work relates to the monitoring of the knowledge source innovation by means of KB engineering and improvement of the methodology of prediction using neural networks.
Keywords: Electrical engineering, Increment analysis, Innovation, Knowledge Source (KS)

Ivan M. Trajić, Ljubiša Vukosavljević1, Bora Novaković, Dragana Ćirić, Aleksandar Dobrosavljević, Dragan Munitlak
Control System of ECR Ion Source Within FAMA
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DOI: 10.2298/SJEE1603423T
Abstract: Recent upgrading of the Facility for Modification and Analysis of Materials with Ion Beams (FAMA), in the Laboratory of Physics of the Vinča Institute of Nuclear Sciences, included modernization of its electron cyclotron resonance (ECR) ion source. The ECR ion source was extensively used for production of multiply charged ions from gases and solid substances for more than 15 years, during which time its major subsystems were expended and therefore, it required complete reconstruction. As a part of this reconstruction we designed and put together a completely new control system of the ECR ion source. It is a distributed and fiber-optically linked control system based on the Group3 Control hardware and the control application written in the Wonderware’s InTouch software. The control system should help and assist an operator in obtaining the appropriate operating parameters of the ECR ion source, maintaining and controlling operating parameters of the machine during its operation, as well as in monitoring weather the safety conditions are fulfilled during the operation of the machine. We tested the operation and performances of the new control system during the commissioning of the upgraded ECR ion source. Compared to the old one, the new system is more reliable, more user-friendly oriented, and it comprises several new useful control applications.
Keywords: Control system design, user interface, ion source.

Milić Djekić
Retraction Notice to: Influence of External Disturbances to Dynamic Balance of the Semi-Anthropomimetic Robot
Download PDF file: (56.63 KB)
DOI: 10.2298/SJEE1603435E

©2016 Serbian Journal of Electrical Engineering