Vol. 13, No. 1, February 2016


Miloš Kostić, Nebojša Dončov, Biljana Stošić, Bratislav Milovanović
Digital Filter-based 1D TLM Model of Dispersive Anisotropic Conductivity Panel
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DOI: 10.2298/SJEE1601001K
Abstract: One-dimensional (1D) Transmission Line Matrix (TLM) method with Z-transforms, is applied in the paper to allow for an efficient time-domain simulation of thin anisotropic conductive panel of dispersive behavior. It uses a digital filter model to incorporate the scattering coefficients of the panel at two TLM cells interface in order to avoid a fine meshing of panel thickness. Model validation is done for a panel made of carbon-fibre material whose electric conductivity is anisotropic and assumed to be frequency dependent according to the Drude model. Fine TLM mesh results are used to verify the model accuracy.
Keywords: 1D TLM method, Bilinear Z-transform, Digital filter, Carbon-fibre, Anisotropic conductivity, Drude model.

Zaviša Gordić, Claudio Ongaro
Calibration of Robot Tool Centre Point using Camera-based System
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DOI: 10.2298/SJEE1601009G
Abstract: Robot Tool Centre Point (TCP) calibration problem is of great importance for a number of industrial applications, and it is well known both in theory and in practice. Although various techniques have been proposed for solving this problem, they mostly require tool jogging or long processing time, both of which affect process performance by extending cycle time. This paper presents an innovative way of TCP calibration using a set of two cameras. The robot tool is placed in an area where images in two orthogonal planes are acquired using cameras. Using robust pattern recognition, even deformed tool can be identified on images, and information about its current position and orientation forwarded to control unit for calibration. Compared to other techniques, test results show significant reduction in procedure complexity and calibration time. These improvements enable more frequent TCP checking and recalibration during production, thus improving the product quality.
Keywords: Robot TCP calibration, Camera system, Smart factories.

Milomir Tatović, Saša Adamović, Milan Milosavljević
Implementation Theoretical Information Protocol for Public Distribution Cryptology Keys
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DOI: 10.2298/SJEE1601021T
Abstract: This paper presents the design and implementation of a key distribution protocol over public channels. This protocol has its own source of randomness, based on data from civil air traffic. An equivalent protocol scheme has been developed according to the theoretical protocol, “satellite scenario”. Both parties to generate symmetric keys without preshared secrets have been allowed. Keys generated in this way can be used with symmetric encryption (AES, DES). The performance of the proposed protocol has been conducted with rigorous theoretical information analysis.
Keywords: Key Exchange, Perfect Protocol, Satellite Scenario.

Mihailo Vesović, Aleksandra Smiljanić, Dušan Kostić
Performance of Shortest Path Algorithm Based on Parallel Vertex Traversal
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DOI: 10.2298/SJEE1601031V
Abstract: Shortest path algorithms for different applications, such as Internet routing, VLSI design and so on are used. Dijkstra and Bellman-Ford are commonly used shortest path algorithms which are typically implemented in networks with hundreds of nodes. However, scale of shortest path problems is increasing, and more efficient algorithms are needed. With the development of multicore processors, one natural way to speedup shortest path algorithms is through parallelization. In this paper, we propose a novel shortest path algorithm with parallel vertex transversal, and compare its speed with standard solutions in datacenter topologies.
Keywords: Parallelization, Shortest Path Algorithms, Single Source Shortest Path, Bellman-Ford, Dijkstra

Aleksandar Demić, Jelena Radovanović, Vitomir Milanović
Analysis of Dipole Matrix Element in Quantum Well and Quantum Cascade Laser under the Influence of External Magnetic Field
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DOI: 10.2298/SJEE1601045D
Abstract: We present a method for modeling nonparabolicity effects (NPE) in quantum nanostructures by using second order perturbation theory. We will analyze application of this model on a quantum well without external electric field and a quantum cascade laser (QCL). This model will allow us to examine the influence of magnetic field on dipole matrix element in QCL structures which will give better insight how NPE can disrupt gain of QCL structures.
Keywords: Quantum cascade lasers, Nonparabolicity effects.

Miljan Petrović, Milica Jovanović
Realization of Universal Periodic Sequence Generator on FPG
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DOI: 10.2298/SJEE1601059P
Abstract: This paper presents mathematical modeling and performance evaluation of different realizations of universal periodic digital signal generator based on infinite impulse response filter. The development kit used was Spartan 3E-Starter Board. Using Xilinx software environment and VHDL, the generator has been described and then synthesized and implemented on FPGA chip on the board. Included realizations are direct form II (canonical form) of the filter, as well as hardware optimized single register structure with different control mechanism. Comparative analysis of these two digital systems points to their differences, advantages and weaknesses. Keywords: FPGA, IIR filter, Signal generator, VHDL.
Keywords: FPGA, IIR filter, Signal generator, VHDL.

Marjan Urekar, Marina Bulat, Bojan Vujičić, Dragan Pejić
Composite Resistor Standard for Calibration of Measuring Transducers in Laboratory Conditions
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DOI: 10.2298/SJEE1601071U
Abstract: Calibration of measuring transducers for precision measurement is done by measuring voltage drop at the resistor standard, produced by output dc current proportional to the input measured value. Resistance fluctuations due to the temperature coefficient of the resistor standard are minor, thanks to the stable temperature conditions in laboratory environment. This fact brings the need to calculate the effect of resistor self-heating on its resistance. This thermal effect, produced by the flow of current through the resistor, is often disregarded. For the precise measurements this can be a significant source of error and must be quantified. This paper describes mathematical model of measurement error, resistor self-heating coefficient is defined, as it’s not usually given in product datasheets. The effect on measurement results is given in detail. Composite resistor standard prototype is described, made from off-the-shelf mass produced components, calculated and hand selected to cancel the self-heating coefficient effects. The prototype is compared to the existing commercially available high performance resistor standard.
Keywords: Calibration, Temperature coefficient, Limit of error, Transducer, Metrology, Instrumentation, Composite resistor standard.

Bogdan Marković, Jelena Ćertić
FPGA Realization of Farrow Structure for Sampling Rate Change
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DOI: 10.2298/SJEE1601083M
Abstract: In numerous implementations of modern telecommunications and digital audio systems there is a need for sampling rate change of the system input signal. When the relation between signal input and output sampling frequencies is a fraction of two large integer numbers, Lagrange interpolation based on Farrow structure can be used for the efficient realization of the resample block. This paper highlights efficient realization and estimation of necessary resources for polynomial cubic Lagrange interpolation in the case of the demand for the signal sampling rate change with the factor 160/147 on Field-Programmable Gate Array architecture (FPGA).
Keywords: Farrow structure, Lagrange interpolation, Finite Impulse Response (FIR), Field-Programmable Gate Array (FPGA), Sampling Rate Change (SCR), implementation, Estimation of necessary resources.

Aleksandra J. Krneta, Branko M. Kolundžija
Analysis of Axially Symmetric Wire Antennas by the Use of Exact Kernel of Electric Field Integral Equation
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DOI: 10.2298/SJEE1601095K
Abstract: The paper presents a new method for the analysis of wire antennas with axial symmetry. Truncated cones have been applied to precisely model antenna geometry, while the exact kernel of the electric field integral equation has been used for computation. Accuracy and efficiency of the method has been further increased by the use of higher order basis functions for current expansion, and by selecting integration methods based on singularity cancelation techniques for the calculation of potential and impedance integrals. The method has been applied to the analysis of a typical dipole antenna, thick dipole antenna and a coaxial line. The obtained results verify the high accuracy of the method.
Keywords: Wire antennas, Exact kernel, Electric field integral equation, Method of moments.

Miloš S. Stanković, Srdjan S. Stanković, Karl Henrik Johansson
A Consensus-Based Distributed Calibration Algorithm for Sensor Networks
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DOI: 10.2298/SJEE1601111S
Abstract: In this paper a novel distributed algorithm for blind macro-calibration in sensor networks based on consensus is proposed. The algorithm is formulated as a set of gradient-type recursions for estimating parameters of sensor calibration functions, starting from local criteria defined as weighted sums of mean square differences between the outputs of neighboring sensors. It is proved that the algorithm achieves asymptotic agreement for sensor gains and offsets in the mean square sense and with probability one. In the case of additive measurement noise, additive inter-agent communication noise and communication outages, a modification of the original algorithm is proposed. It is proved using stochastic approximation arguments that the modified algorithm achieves asymptotic consensus for sensor gains and offsets in the mean square sense and with probability one. Special attention is paid to the situation when one sensor is selected as a reference. Illustrative simulation examples are provided.
Keywords: Calibration, Sensor Networks, Consensus, Stochastic Approximation, Convergence.

Mihajlo Tatović, Alenka Milovanović, Ivan Karapandžić
Device for the Remote Measurement of Meteorological Data Based on Arduino Platform
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DOI: 10.2298/SJEE1601133T
Abstract: The aim of this paper is to present a realization of a device for displaying, monitoring, and recording non-electrical quantities relevant to the determination and examination of weather conditions. The main unit of this device is the Arduino platform, which controls digital sensors and the GSM module used for communication with user. To accomplish that, the GSM module responds to SMS with the current values of parameters that are being monitored. Also, it uses the GPS service, which allows an Internet connection and sends data back to the Web application. When the Web application receives these data, it processes them and saves them in a MySQL database. The device has the ability to record data on an SD card. A user application is created in C# programming language and allows reading of the recorded data from the SD card and handling of such data. All of results obtained by this device is compared with the results gathered by the Republic Hydrometeorogical Service of Serbia.
Keywords: Meteorological station, Arduino platform, GSM module, User application, Database, Remote measuring, Web application.

©2016 Serbian Journal of Electrical Engineering