Loxodromic Antenna Arrays Based on Archimedean Spiral

A loxodromic antenna array is a spiral array on the spherical surface. Distribution of elementary antennas on the spherical surface was made by following loxodromic curves. This type of antenna array offers a wide range of opportunities in the variation of their radiation patterns through antenna distribution and phase control. The paper studies different loxodromic antenna arrays based on the influence of an Archimedean spiral configuration pattern on the radiation pattern of a spherical antenna array. Analysis was made using a developed moment method program with a spectral-domain approach

Adaptivna tehnika obrade slike za kontrolu kvalitete u proizvodnji keramičkih pločica

Automation of the visual inspection for quality control in production of materials with textures (tiles, textile, leather, etc.) is not widely implemented. A sophisticated system for image acquisition, as well as a fast and efficient procedure for texture analysis is needed for this purpose. In this paper the Surface Failure Detection (SFD) algorithm for quality control in ceramic tiles production is presented. It is based on Discrete Wavelet Transform (DWT) and Probabilistic Neural Networks (PNN) with radial basis. DWT provides a multi-resolution analysis, which mimics behavior of a human visual system and it extracts from the tile image the features important for failure detection. Neural networks are used for classification of the tiles with respect to presence of defects. Classification efficiency mainly depends on the proper choice of the training vectors for neural networks. For neural networks preparation we propose an automated adaptive technique based on statistics of the tiles defects textures. This technique enables fast adaptation of the SFD algorithm to different textures, which is important for automated visual inspection in the production of a new tile type.Automatizacija vizualne provjere za kontrolu kvalitete u proizvodnji materijala s teksturama (pločice, tekstil, kože, itd.) nije široko primijenjena u praksi. Za ovu namjenu potreban je sofisticirani sustav za snimanje slika, kao i brza i efikasna procedura za analizu tekstura. U ovom je radu predstavljen algoritam za detekciju površinskih oštećenja (SFD) u proizvodnji keramičkih pločica. Temelji se na diskretnoj valićnoj transformaciji (DWT) i probabilističkim neuronskim mrežama (PNN) s radijalnim bazama. DWT omogućava više-rezolucijsku analizu koja oponaša ljudski vizualni sustav i izdvaja iz slike pločice značajne za detekciju oštećenja. Neuronske mreže se koriste za klasifikaciju pločica ovisno o postojanju oštećenja. Efikasnost klasifikacije najviše ovisi o odgovarajućem odabiru vektora za učenje neuronskih mreža. Za pripremu neuronskih mreža predlažemo automatiziranu adaptivnu tehniku koja se temelji na statistici tekstura oštećenja na pločicama. Ova tehnika omogućava brzu adaptaciju SFD algoritma na različite teksture, što je posebno važno za automatiziranu vizualnu provjeru u proizvodnji novog tipa pločica

Adaptivna tehnika obrade slike za kontrolu kvalitete u proizvodnji keramičkih pločica

Automation of the visual inspection for quality control in production of materials with textures (tiles, textile, leather, etc.) is not widely implemented. A sophisticated system for image acquisition, as well as a fast and efficient procedure for texture analysis is needed for this purpose. In this paper the Surface Failure Detection (SFD) algorithm for quality control in ceramic tiles production is presented. It is based on Discrete Wavelet Transform (DWT) and Probabilistic Neural Networks (PNN) with radial basis. DWT provides a multi-resolution analysis, which mimics behavior of a human visual system and it extracts from the tile image the features important for failure detection. Neural networks are used for classification of the tiles with respect to presence of defects. Classification efficiency mainly depends on the proper choice of the training vectors for neural networks. For neural networks preparation we propose an automated adaptive technique based on statistics of the tiles defects textures. This technique enables fast adaptation of the SFD algorithm to different textures, which is important for automated visual inspection in the production of a new tile type.Automatizacija vizualne provjere za kontrolu kvalitete u proizvodnji materijala s teksturama (pločice, tekstil, kože, itd.) nije široko primijenjena u praksi. Za ovu namjenu potreban je sofisticirani sustav za snimanje slika, kao i brza i efikasna procedura za analizu tekstura. U ovom je radu predstavljen algoritam za detekciju površinskih oštećenja (SFD) u proizvodnji keramičkih pločica. Temelji se na diskretnoj valićnoj transformaciji (DWT) i probabilističkim neuronskim mrežama (PNN) s radijalnim bazama. DWT omogućava više-rezolucijsku analizu koja oponaša ljudski vizualni sustav i izdvaja iz slike pločice značajne za detekciju oštećenja. Neuronske mreže se koriste za klasifikaciju pločica ovisno o postojanju oštećenja. Efikasnost klasifikacije najviše ovisi o odgovarajućem odabiru vektora za učenje neuronskih mreža. Za pripremu neuronskih mreža predlažemo automatiziranu adaptivnu tehniku koja se temelji na statistici tekstura oštećenja na pločicama. Ova tehnika omogućava brzu adaptaciju SFD algoritma na različite teksture, što je posebno važno za automatiziranu vizualnu provjeru u proizvodnji novog tipa pločica

Radiation Pattern of Waveguide Antenna Arrays on Spherical Surface - Experimental Results

In this paper, the radiation pattern of two experimental models of circular waveguide antenna arrays on spherical surface is obtained experimentally and compared with theoretical patterns. We have omitted the phase delay of feed system signals because we have only compared measured and theoretical results in order to verify theoretical results, without trying to improve the best radiation characteristics of developed experimental models. Analysis was made with a developed moment method (MoM) program. The spectral-domain approach to the analysis of the spherical antenna arrays is briefly presented in the paper. Measurements were not performed in a well-defined anechoic environment

EXPERIMENTAL SHIELDING EFFECTIVENESS STUDY OF METAL ENCLOSURE WITH ELECTROMAGNETIC ABSORBER INSIDE

In this paper, the impact of an electromagnetic absorber inside a protective metal enclosure is analyzed. The absorber is put inside the enclosure in order to improve its shielding effectiveness, especially at the first resonant frequency. Different absorber's sheet positions inside the enclosure are analyzed. The absorber sheet dimensions are fitted to correspond the enclosure's walls. The experimental procedure is conducted in a semi-anechoic room. The numerical TLM simulations of the EM filed distribution inside enclosure are conducted in order to consider position of the absorber sheet on different walls

Ultra-wideband systems with orthogonal coded differential TR receiver

U ovom je radu predstavljen kodirani diferencijalni TR (cDTR) prijemnik koji mapiranjem informacije u K različitih ortogonalnih kodova omogućuje prijenos dodatnog bita. Svojstva kodiranog DTR-a su analizirana i uspoređena s konvencionalnim DTR-om. Kroz analizu je dana ocjena svojstva prijemnika u smislu vjerojatnosti pogreške bita (BEP), brzine prijenosa i složenosti prijemnika. Rezultati su pokazali da kodirani DTR uz isti BEP omogućuje veću brzinu prijenosa od konvencionalnog DTR-a. Osim toga, razmotrena je i sklopovska složenost prijemnika.This paper presents coded differential TR (cDTR) receiver that transmits extra bit by mapping information in K different orthogonal codes. The performance of the coded DTR is analyzed and compared with the conventional DTR. Throughout the analysis, the performance of receivers in terms of bit error probability (BEP), data rate and receiver complexity are assessed. The results show that coded DTR is able to outperform conventional DTR receiver in terms of data rate maintaining the same BEP. Additionally, the receiver hardware complexity issue is discussed

USPOREDBA PROIZVODNJE BIOPLINA IZMEĐU GNOJA NESILICA I BROJLERA

Biogas plants that process raw materials from agriculture, such as poultry manure, are one of the most significant applications of anaerobic fermentation. In Asian countries, particularly in China, India, Nepal and Vietnam, there are several million very simple, small biogas plants that produce gas for household cooking and lighting. In Europe and North America a number of agricultural biogas plants now, are increasing daily, a few thousand biogas plants exist, most of which use modern technologies, anaerobic fermentation. The aim of this paper is to determine the possibility of biogas production from poultry manure with 10% of total solids and through the segments of the quality and quantity, determine the content of total solids (DM), volatile solids (OM), and the amount and composition of biogas. The aim was also to justify the use of poultry manure in biogas production and its application for specific purposes Laboratory research showed that 1 kg of poultry 10% of poultry manure produced 47.01 l of biogas during the 40 days of anaerobic fermentation under mezofilic conditions. Production of biogas has a good potential for development in Croatia, especially in the continental part. Usages of this technology are multiple because of the fact that the Republic of Croatia imports most of the energy. Usage of biogas would reduce the import of certain energy and thus reduce energy dependence; it would increase the number of employers and ease the obligation of Croatia toward EU in replacing some fossil fuels with renewable ones.Bioplinski pogoni koji prerađuju sirovine iz poljoprivrede, poput izmeta peradi, predstavljaju jednu od najvažnijih primjena anaerobne fermentacije. Samo u azijskim zemljama, osobito u Kini, Indiji, Nepalu i Vijetnamu, postoji nekoliko milijuna vrlo jednostavnih, malih bioplinskih reaktora koji proizvode plin za kuhanje i rasvjetu kućanstava. U Europi i Sjevernoj Americi svakodnevno raste broj poljoprivrednih bioplinskih pogona, a danas ih funkcionira nekoliko tisuća, od kojih se većina koristi suvremenim tehnologijama anaerobne fermentacije. Cilj rada je utvrditi mogućnost proizvodnje bioplina iz pilećega gnoja s 10% suhe tvari. S pomoću segmenata kvalitete i kvantitete tijekom istraživanja utvrditi udio suhe tvari (ST), organske tvari (OT), količinu i sastav bioplina te dokazati opravdanost uporabe pilećega gnoja u proizvodnji bioplina i njegove primjene u određene svrhe. Na temelju provedenoga laboratorijskoga istraživanja, dokazana je proizvodnja bioplina iz izmeta peradi i svinjske gnojovke. Anaerobnom fermentacijom u trajanju od 40 dana pri mezofilnim uvjetima proizvedeno je iz 1 kg izmeta nesilica 25 litara bioplina, a iz svinjske gnojovke u kombinaciji s 10% brojlerskoga stajnjaka 47,01 litara bioplina. Proizvodnja bioplina ima dobre uvjete za razvoj u Republici Hrvatskoj, posebice u kontinentalnome dijelu. Koristi od te tehnologije višestruke su, jer je RH prisiljena uvoziti većinu energenata. Korištenjem bioplina smanjio bi se uvoz pojedinih energenata, čime bi se umanjila i energetska ovisnost o drugim državama; povećao bi se broj zaposlenih i RH bi ostvarila lakše svoju obvezu prema EU-u, da zamijeni dio fosilnih goriva obnovljivima

USPOREDBA PROIZVODNJE BIOPLINA IZMEĐU GNOJA NESILICA I BROJLERA

Biogas plants that process raw materials from agriculture, such as poultry manure, are one of the most significant applications of anaerobic fermentation. In Asian countries, particularly in China, India, Nepal and Vietnam, there are several million very simple, small biogas plants that produce gas for household cooking and lighting. In Europe and North America a number of agricultural biogas plants now, are increasing daily, a few thousand biogas plants exist, most of which use modern technologies, anaerobic fermentation. The aim of this paper is to determine the possibility of biogas production from poultry manure with 10% of total solids and through the segments of the quality and quantity, determine the content of total solids (DM), volatile solids (OM), and the amount and composition of biogas. The aim was also to justify the use of poultry manure in biogas production and its application for specific purposes Laboratory research showed that 1 kg of poultry 10% of poultry manure produced 47.01 l of biogas during the 40 days of anaerobic fermentation under mezofilic conditions. Production of biogas has a good potential for development in Croatia, especially in the continental part. Usages of this technology are multiple because of the fact that the Republic of Croatia imports most of the energy. Usage of biogas would reduce the import of certain energy and thus reduce energy dependence; it would increase the number of employers and ease the obligation of Croatia toward EU in replacing some fossil fuels with renewable ones.Bioplinski pogoni koji prerađuju sirovine iz poljoprivrede, poput izmeta peradi, predstavljaju jednu od najvažnijih primjena anaerobne fermentacije. Samo u azijskim zemljama, osobito u Kini, Indiji, Nepalu i Vijetnamu, postoji nekoliko milijuna vrlo jednostavnih, malih bioplinskih reaktora koji proizvode plin za kuhanje i rasvjetu kućanstava. U Europi i Sjevernoj Americi svakodnevno raste broj poljoprivrednih bioplinskih pogona, a danas ih funkcionira nekoliko tisuća, od kojih se većina koristi suvremenim tehnologijama anaerobne fermentacije. Cilj rada je utvrditi mogućnost proizvodnje bioplina iz pilećega gnoja s 10% suhe tvari. S pomoću segmenata kvalitete i kvantitete tijekom istraživanja utvrditi udio suhe tvari (ST), organske tvari (OT), količinu i sastav bioplina te dokazati opravdanost uporabe pilećega gnoja u proizvodnji bioplina i njegove primjene u određene svrhe. Na temelju provedenoga laboratorijskoga istraživanja, dokazana je proizvodnja bioplina iz izmeta peradi i svinjske gnojovke. Anaerobnom fermentacijom u trajanju od 40 dana pri mezofilnim uvjetima proizvedeno je iz 1 kg izmeta nesilica 25 litara bioplina, a iz svinjske gnojovke u kombinaciji s 10% brojlerskoga stajnjaka 47,01 litara bioplina. Proizvodnja bioplina ima dobre uvjete za razvoj u Republici Hrvatskoj, posebice u kontinentalnome dijelu. Koristi od te tehnologije višestruke su, jer je RH prisiljena uvoziti većinu energenata. Korištenjem bioplina smanjio bi se uvoz pojedinih energenata, čime bi se umanjila i energetska ovisnost o drugim državama; povećao bi se broj zaposlenih i RH bi ostvarila lakše svoju obvezu prema EU-u, da zamijeni dio fosilnih goriva obnovljivima

Measuring the Dielectric Constant of Paper Using a Parallel Plate Capacitor

This article is a result of measuring the dielectric constant of a dielectric used in studying the influence of dielectrics on the antennae reflection coefficients. A paper having a density of 0.797 g/cm3, moisture content of 0% and temperature of 210C, is used as a dielectric. Although the literature provides a lot of data on the dielectric properties of wood and paper, without direct measurement of the dielectric constant it is impossible to know its amount for the dielectric used in the defined frequency range. Dielectric constant measurements are performed in the frequency range from 100 Hz to 100 kHz, while the frequency range of its impact on the aperture antenna reflection coefficients is up to 2 GHz. The frequency range from 100 KHz to 10 GHz is interpolated and fitted by using measurements and available literature data and by respecting physical influences and phenomena and functional changes of the dielectric constant of paper within the given range

Circular waveguide antenna arrays on spherical structures

Konformni antenski nizovi, odnosno konformne antene su nizovi koji se prilagođavaju podlozi na koju su postavljene. Kao antenski elementi konformnih nizova u mikrovalnom frekvencijskom području često se koriste otvori na konformnoj strukturi. Valovodom pobuđeni otvori su poznati po velikoj širini glavne latice, simetričnom polju kod antenskog skeniranja, dobrom prilagođenju impedancije (admitancije) te karakteristici ponašanja visokopropusnog filtra (zbog granične frekvencije valovodnih modova). Veliki kut skeniranja uz dovoljno male dimenzije jedna su od važnijih karakteristika konformnih nizova s otvor antenama. U radu su teoretski analizirani i eksperimentalno izmjereni su bitni parametri antenskih nizova na sfernoj podlozi pri čemu su kao elementarne antene korišteni valovodi kružnog poprečnog presjeka. U svrhu analize razvijen je teorijski model, odnosno numerička metoda zasnovana na numeričkom rješavanju integralne jednadžbe za magnetsko (električno) polje primjenom metode momenata. Spektralnom metodom je trodimenzionalni problem transformiran u spektar jednodimenzionalnih problema, što je znatno pojednostavilo i ubrzalo rješavanje analiziranih problema. Pri izračunu parametara niza korištene su Greenove funkcije za sferne strukture u spektralnoj domeni. Na temelju razvijene metode analize izrađen je računalni program za izračun ulazne admitancije, sprege između valovoda na sferi te dijagrama zračenja (i polarizacije) valovodnih antenskih nizova na sfernoj podlozi. Da bi se pri izračunu sprege izbjegli numerički problemi, uvedene su modificirane vektor- Legendreove transformacije i normalizirani Legendreovi polinomi. Osim toga, pri izračunima su korišteni asimptotski izrazi za Besselove i Hankelove funkcije. Pri izračunu sprege uvedena je nova metoda kod koje su, korištenjem analogije sa metodom potencijala te adicionog teorema za sferne harmonike, određeni izrazi za ekvivalentne struje u spektralnoj domeni na otvoru valovoda. Ovom metodom je značajno smanjeno vrijeme za izračun koeficijenata sprege. Utjecaj zakrivljenosti podloge na parametre antene razmatran je izračunom svih bitnih parametara valovodnog antenskog niza na sferi (ulazna admitancija, koeficijenti sprege, međuadmitancija i dijagramim zračenja) i usporedbom istih za različite radijuse sferne podloge. Teorijski model je verificiran izveden korištenjem mjerenih rezultata iz dostupne literature te mjerenjem na izvedenim laboratorijskim modelima (dva planarna i dva sferoidalna modela). Na oba laboratorijska modela načinjena su mjerenja sprege i dijagrama zračenja. Ova mjerenja nisu izvedena u bezječnoj komori, što je rezultiralo na pojavom neželjenih reflektiranih valova, a time i odstupanjima i valovitosti u izmjerenim karakteristikama antene. U svim izmjerenim slučajevima postignuto je dobro poklapanje izračunatih i izmjerenih rezultata, čime je potvrđena ispravnost teorijskog modela i prema njemu izvedenog računalnog programa.considerations other than electromagnetics. Usually, a conformal antenna is cylindrical, spherical or some other shape, with radiating elements mounted on or integrated into the smoothly curved surface. Radiation elements – elementary antennas of these arrays are usually used aperture antennas. Apertures are microwave antennas that are usually loaded with rectangular or cylindrical waveguides. The radiation pattern of a single waveguide opening is very broad. In the thesis we studied a spherical array of circular waveguides antennas with the apertures placed on the spherical surface. The analysis is based on solving the integral equation for a magnetic field by using the moment method (MoM). The solution procedure takes advantage of the spectral domain approach where a three-dimension problem is transformed into spectral of much simpler onedimension problem. The antenna structure is rigorously taken into account by using proper Green’s functions, and the array is fully analyzed by using the element-by-element approach. A theoretical model to determine solutions for a radiation pattern, mutual coupling and input admittance was developed. We have also made the program for calculating radiation pattern, mutual coupling and input admittance of spherical waveguide arrays based on the developed MoM and spectral-domain approach. In order to avoid numerical problems, when we calculate mutual coupling, a modified vector- Legendre transformation and normalized Legendre polynomials are defined and applied to the solution procedure. We have also used asymptotic equations for Bessel and Hankel functions. This thesis demonstrates a novel approach to mutual coupling within the MoM analysis of spherical arrays by expressing the equivalent current on the waveguide aperture in terms of two suitable potential-like auxiliary functions. The new approach results in significant acceleration of the analysis of spherical antenna arrays. The influence of structure radius on input impedance, mutual coupling and radiation pattern was also investigated. In the proces of verifying theoretical results we had to built two planar and two spherical experimental models. On the spherical surface, antenna elements are placed at equidistant positions on the surface of the icosahedron. The developed theoretical model and program have been verified against measurements and results from the literature. Measurement was not performed in a well-defined anechoic chamber. The results show a very good agreement between the measured and the calculated results