András Fehér

56363584800

Publications - 9

Multiresolution modeling of cavity resonators in microwave systems

András Fehér Brigita Sziová János Pipek Szilvia Nagy

Publication Name: 2016 13th International Conference on Synthesis Modeling Analysis and Simulation Methods and Applications to Circuit Design Smacd 2016

Publication Date: 2016-07-25

Volume: Unknown

Issue: Unknown

Page Range: Unknown

Description:

Multiresolution analysis or wavelet analysis provides a toolbox not only for signal processing, but also for synthesis of complex systems. Wavelets can be used for modeling complex parts of microwave circuits, such as cavity resonators. The differential equations describing the physical behavior of the device can be discretized using multiple resolutions simultaneously, i.e., high resolutions, where the details of the geometry demand it, and low resolutions, where the geometry is smooth. Using wavelet analysis offers the possibility of systematic and adaptive refinement, where the result is not sufficiently precise. Our method gives an approximation for the error of the solution in order to make it possible to decide, whether refinements are necessary.

Open Access: Yes

DOI: 10.1109/SMACD.2016.7520651

Wavelet analysis and finite difference modeling of multiple reflections in transmission lines

A. Bekefi András Fehér Szilvia Nagy

Publication Name: 2nd Middle East Conference on Antennas and Propagation Mecap 2013

Publication Date: 2012-01-01

Volume: Unknown

Issue: Unknown

Page Range: Unknown

Description:

No description provided

Open Access: Yes

DOI: 10.1109/MECAP.2012.6618201

Error estimation of wavelet based modeling of electromagnetic waves in waveguides and resonators

András Fehér János Pipek Szilvia Nagy

Publication Name: 2nd Middle East Conference on Antennas and Propagation Mecap 2013

Publication Date: 2012-01-01

Volume: Unknown

Issue: Unknown

Page Range: Unknown

Description:

Wavelets provide an effective toolbox for solving differential equations by representing the continuous functions by their wavelet expansion coefficients and the corresponding differential equations by discrete matrix equations. The wavelet basis functions are organized into resolution levels of different frequency terms at different locations, and the main advantage of the wavelet expansion representation is that the resolution level can be different at different locations, if the solution function contains higher frequency terms in one place and restricted to lower frequencies at other places. Wavelet based differential equation solving methods can be adaptive, it is possible to refine the solution locally, if the precision is not sufficient at some regions. In the present work a simple method for estimating the next resolution level wavelet coefficients is presented. Predicting the approximate value of these coefficients makes it possible to select the minimal set of wavelet basis functions for the next resolution level solution in a computationally economic way, or in the last resolution levels it can substitute the next level solution of the matrix equation. © 2012 IEEE.

Open Access: Yes

DOI: 10.1109/MECAP.2012.6618193

Developing sample holders for measuring shielding effectiveness of thin layers on compound semiconductor substrates

András Fehér Szilvia Nagy

Publication Name: Progress in Electromagnetics Research Symposium

Publication Date: 2011-12-26

Volume: Unknown

Issue: Unknown

Page Range: 1637-1641

Description:

Wavelet or multiresolution analysis (MRA) is widely applied in advanced data compression algorithms, solving differential equations, and some approaches have already applied this technique in describing electromagnetic fields. The main advantage of the application of MRA is its adaptivity and flexibility. Since the details of the electromagnetic field are not distributed equally over different parts of the system (i.e., the description of some parts need finer details, while others are easily represented at low resolution level), locally different resolution levels can be applied. Wavelet based adaptive solution possibilities of differential equations of electromagnetic field are investigated in the followings. The adaptivity of the method means in this case, that the refinement level of the solution can be increased locally, if the accuracy needs it, during the calculations. The applicability of the eigenvalue-type differential equation solving method is illustrated by solution of microwave wave-equations of cavity resonators.

Open Access: Yes

DOI: DOI not available

Structural entropy based localization study of wavelet transformed AFM images for detecting background patterns

András Fehér László Milán Molnár Szilvia Nagy

Publication Name: Progress in Electromagnetics Research Symposium

Publication Date: 2011-12-26

Volume: Unknown

Issue: Unknown

Page Range: 1284-1288

Description:

By defining the structural entropy the von Neumann entropy of a charge distribution on a finite grid is divided into two parts. The first one, the extension entropy, is simply the logarithm of the occupation number (i.e., the number of the average grid sites occupied by the charge distribution), while the second part is the structural entropy itself. On a structural entropy versus participation ratio map the different types of localizations follow different, well characterized curves, and every distribution is represented by a vector on the map. By a structural entropy-filling factor map of any charge distributions on a finite grid (e.g., finite representation of an electron density, or a grayscale atomic force microscope (AFM) image) superstructures of different scale topologies with different decay types can be traced as well. However it is rather hard to distinguish elements of an additive superstructure, especially if the numerical parameters of the different scale patterns are necessary. In the AFM practice the background patterns are sometimes hard to compensate, and by simple structural entropy based calculations it is almost impossible to separate the superstructure of the atomic scale and the image-scale pattern. The reason is the following. Superstructures manifest on the structural entropy map as sum of the sub-structures vector, thus since none of the structures are known, only the sum of their vectors, the sub-vectors are not unique. Multiresolution or wavelet analysis (MRA) uses a system of basis functions with various time and frequency (space and spatial frequency) parameters for expanding functions. This system makes the time-frequency localization possible. Using some selected MRA resolution levels of the AFM image and carrying out the structural entropy based localization study on each of these levels will determine the decay type of the image at the length scales corresponding to the selected frequencies. This approach is promising for determining the large-scale patterns on AFM pictures.

Open Access: Yes

DOI: DOI not available

Controlled bidirectional energy transfer by ultracapacitors in electric drive

Zoltán Puklus András Fehér

Publication Name: 12th IEEE International Symposium on Computational Intelligence and Informatics Cinti 2011 Proceedings

Publication Date: 2011-12-01

Volume: Unknown

Issue: Unknown

Page Range: 31-34

Description:

This paper shows the possibility of the two-directional energy transfer between energy sources using the example of ultracapacitors. The showed method allows bidirectional energy transfer between power systems which use different voltage levels. We used PSIM program to simulate the bidirectional energy transfer and study the operation of the applied model. © 2011 IEEE.

Open Access: Yes

DOI: 10.1109/CINTI.2011.6108526

Topology analysis of scanning microscope images with structural entropy and discrete wavelet transform

András Fehér Szilvia Nagy

Publication Name: International Conference on Systems Signals and Image Processing

Publication Date: 2011-11-02

Volume: Unknown

Issue: Unknown

Page Range: 101-104

Description:

Topology free structure of scanning electron microscopy images of heat treated, metallized compound semiconductor surfaces are studied using structural entropy based analysis. The scale dependence and the possible superstructures are determined by wavelet transforming the images before the localization type detection. The studied images are taken in-situ during a thermalization experiment, using GaAs as a substrate and gold, zinc and SiO2 layers of 60 to 100 nm thickness. © 2011 Univ of Sarajevo.

Open Access: Yes

DOI: DOI not available

On wavelet based modeling of radio frequency circuits, parts and electromagnetic fiels

András Fehér Szilvia Nagy

Publication Name: 2010 11th International Workshop on Symbolic and Numerical Methods Modeling and Applications to Circuit Design Sm2acd 2010

Publication Date: 2010-12-01

Volume: Unknown

Issue: Unknown

Page Range: Unknown

Description:

Multiresolution or wavelet analysis is widely used in advanced data compression algorithms, and some approaches applied this technique in describing electromagnetic fields. The main goal of the application of MRA is its flexibility, i.e., since the details of the electromagnetic field are not distributed equally over different parts of the system, thus locally different resolution level can be applied. Wavelet based adaptive solution possibilities of differential equations of electromagnetic field are investigated in the followings. The adaptivity of the method means in this case, that the refinement level of the solution can be increased locally, if the accuracy needs it, during the calculations. ©2010 IEEE.

Open Access: Yes

DOI: 10.1109/SM2ACD.2010.5672288

Definitions and measurement of power factor

Zoltán Puklus András Fehér

Publication Name: 8th International Symposium of Hungarian Researchers on Computational Intelligence and Informatics Cinti 2007

Publication Date: 2007-12-01

Volume: Unknown

Issue: Unknown

Page Range: 623-632

Description:

The methodology of measurement of cos was developed long time ago, but it is usable only for sinusoidal voltages and currents. Nowadays the customer loads use power supplies built with semiconductors, switching power supplies, power controlling systems, etc. These loads cause non-sinusoidal current in power lines, energy quality and EMC problems. The method of Power Factor measurement is described in this article, which is a good KPI in these cases.

Open Access: Yes

DOI: DOI not available